Contents

A&A 482, 179-196 (2008)
DOI: 10.1051/0004-6361:20079203

Detection of amino acetonitrile in Sgr B2(N)[*],[*],[*]

A. Belloche1 - K. M. Menten1 - C. Comito1 - H. S. P. Müller1,2 - P. Schilke1 - J. Ott3,4,5 - S. Thorwirth1 - C. Hieret1


1 - Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2 - I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
3 - National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA
4 - California Institute of Technology, 1200 E. California Blvd., Caltech Astronomy, 105-24, Pasadena, CA 91125-2400, USA
5 - CSIRO Australia Telescope National Facility, Cnr Vimiera & Pembroke Roads, Marsfield NSW 2122, Australia

Received 6 December 2007 / Accepted 16 January 2008

Abstract
Context. Amino acids are building blocks of proteins and therefore key ingredients for the origin of life. The simplest amino acid, glycine (NH2CH2COOH), has long been searched for in the interstellar medium but has not been unambiguously detected so far. At the same time, more and more complex molecules have been newly found toward the prolific Galactic center source Sagittarius B2.
Aims. Since the search for glycine has turned out to be extremely difficult, we aimed at detecting a chemically related species (possibly a direct precursor), amino acetonitrile (NH2CH2CN).
Methods. With the IRAM 30 m telescope we carried out a complete line survey of the hot core regions Sgr B2(N) and (M) in the 3 mm range, plus partial surveys at 2 and 1.3 mm. We analyzed our 30 m line survey in the LTE approximation and modeled the emission of all known molecules simultaneously. We identified spectral features at the frequencies predicted for amino acetonitrile lines having intensities compatible with a unique rotation temperature. We also used the Very Large Array to look for cold, extended emission from amino acetonitrile.
Results. We detected amino acetonitrile in Sgr B2(N) in our 30 m telescope line survey and conducted confirmatory observations of selected lines with the IRAM Plateau de Bure and the Australia Telescope Compact Array interferometers. The emission arises from a known hot core, the Large Molecule Heimat, and is compact with a source diameter of 2 $\hbox{$^{\prime\prime}$ }$ (0.08 pc). We derived a column density of 2.8 $\times $ 1016 cm-2, a temperature of 100 K, and a linewidth of 7 km s-1. Based on the simultaneously observed continuum emission, we calculated a density of 1.7 $\times $ 108 cm-3, a mass of 2340 $M_\odot$, and an amino acetonitrile fractional abundance of 2.2 $\times $ 10-9. The high abundance and temperature may indicate that amino acetonitrile is formed by grain surface chemistry. We did not detect any hot, compact amino acetonitrile emission toward Sgr B2(M) or any cold, extended emission toward Sgr B2, with column-density upper limits of 6 $\times $ 1015 and 3 $\times $ 1012-14 cm-2, respectively.
Conclusions. Based on our amino acetonitrile detection toward Sgr B2(N) and a comparison to the pair methylcyanide/acetic acid both detected in this source, we suggest that the column density of both glycine conformers in Sgr B2(N) is well below the best upper limits published recently by other authors, and probably below the confusion limit in the 1-3 mm range.

Key words: astrobiology - astrochemistry - line: identification - stars: formation - ISM: individual objects: Sagittarius B2 - ISM: molecules

   
1 Introduction - general methods

Among the still growing list of complex molecules found in the interstellar medium, so-called ``bio''molecules garner special attention. In particular, the quest for interstellar amino acids, building blocks of proteins, has engaged radio and millimeter wavelength astronomers for a long time. Numerous published and unpublished searches have been made for interstellar glycine, the simplest amino acid (Ceccarelli et al. 2000; Jones et al. 2007; Combes et al. 1996; Hollis et al. 2003,1980; Brown et al. 1979; Berulis et al. 1985; Cunningham et al. 2007). Its recent ``detection'' claimed by Kuan et al. (2003) has been persuasively rebutted by Snyder et al. (2005). Since the early days of molecular radio astronomy, Sagittarius B2 has been a favorite target in searches for complex molecules in space.

   
1.1 The target: Sagittarius B2

Sagittarius B2 (hereafter Sgr B2 for short) is a very massive (several million solar masses) and extremely active region of high-mass star formation at a projected distance of $\sim$100 pc from the Galactic center. Its distance from the Sun is assumed to be the same as the Galactic center distance, R0. Reid (1993), reviewing various methods to determine R0, arrived at a ``best estimate'' of 8.0 $\pm$ 0.5 kpc, a value that we adopt in this article. It is supported by recent modeling of trajectories of stars orbiting the central black hole, which yields 7.94 $\pm$ 0.42 kpc (Eisenhauer et al. 2003).

There are two major centers of activity, Sgr B2(M) and Sgr B2(N) separated by $\sim$2 pc. In each of them, recent star formation manifests itself in a multitude of H II regions of many sizes, from hypercompact to compact (Gaume et al. 1995), and there is abundant material to form new stars evident by massive sources of molecular line emission and submillimeter continuum emission from dust (Lis et al. 1991,1993).

   
1.1.1 Sgr B2 as part of the Central Molecular Zone

Some of the first detections of interstellar organic molecules (at cm-wavelengths!) were made toward Sgr B2 (see Menten 2004, for a historical perspective). The low intrinsic line strengths make these cm lines unlikely candidates for detection. However, the situation is helped, first, by the fact that many of the transitions in question may have inverted levels (Menten 2004) and amplify background radio continuum emission which is very intense at cm wavelengths (Hollis et al. 2007). Second, the spatial distributions of many species are characterized by spatially extended emission covering areas beyond Sgr B2 itself, filling single dish telescope beams, thus producing appreciable intensity even when observed with low spatial resolution (Jones et al. 2008; Cummins et al. 1986). This emission is characterized by low rotation temperatures, favoring lower frequency lines. Recent identifications of ``new'' species include glycolaldehyde CH2OHCHO (Hollis et al. 2001,2000), ethylene glycol HOCH2CH2OH (Hollis et al. 2002), and vinyl alcohol CH2CHOH (Turner & Apponi 2001).

Sgr B2 and its surroundings are part of the Central Molecular Zone (CMZ) of our Galaxy, a $\sim$ $\pm 0\hbox{$.\!\!^\circ$ }3$ latitude wide band stretching around the Galactic center from longitude $l \sim +1\hbox{$.\!\!^\circ$ }6$ to $-1\hbox{$.\!\!^\circ$ }1$ (see, e.g., Morris & Serabyn 1996). The CMZ contains spatially extended emission of many complex organic molecules (Dahmen et al. 1997; Menten 2004; Requena-Torres et al. 2006; Minh et al. 1992).

   
1.1.2 The Large Molecule Heimat

Near Sgr B2(N), there is a hot, dense compact source that has a mm-wavelength line density second to no other known object. This source, for which Snyder et al. (1994) coined the name ``Large Molecule Heimat'' (LMH), is characterized by very high densities (>107 cm-3) and gas temperatures (>100 K). In recent years arcsecond resolution interferometry with the BIMA array has resulted in the detection and imaging of increasingly complex organic species toward the LMH, such as vinyl cyanide CH2CHCN, methyl formate HCOOCH3, and ethyl cyanide CH3CH2CN (Miao et al. 1995; Miao & Snyder 1997), formamide NH2CHO, isocyanic acid HNCO, and methyl formate HCOOCH3 (Kuan & Snyder 1996), acetic acid CH3COOH (Mehringer et al. 1997; Remijan et al. 2002), formic acid HCOOH (Liu et al. 2001), and acetone (CH3)2CO (Snyder et al. 2002). All the interferometric observations are consistent with a compact (<few arcsec diameter) source that had already been identified as the source of high-density-tracing non-metastable ammonia line emission by Vogel et al. (1987) and thermal methanol emission by Mehringer & Menten (1997, their source ``i''). The LMH also hosts a powerful H2O maser region (Reid et al. 1988), which provides evidence that it is very young (see Sect. 4.1).

1.2 The complex spectra of complex molecules

Complex molecules in general have large partition functions, in particular for the elevated temperatures (>100 K) in molecular hot cores, dense and compact cloud condensations internally heated by a deeply embedded, young high-mass (proto)stellar object. Therefore, most individual spectral lines are weak and might easily get hidden in the ``line forest'' found toward these frequently extremely line-rich sources. To a large part, this forest consists of rotational lines, many of them presently unidentifiable, from within relatively low-lying vibrational states of molecules. Most of the candidate molecules from which these lines originate are known to exist in these sources, but laboratory spectroscopy is presently lacking for lines from the states in question. At this point in the game, unequivocally identifying a species in a spectrum of a hot core covering a wide spectral range requires the following steps: as described in detail in Sect. 3.2, assuming Local Thermodynamic Equilibrium (LTE) (which applies at the high densities in hot cores) a model spectrum is calculated for an assumed rotation temperature, column density, line width and other parameters. This predicts lines of a given intensity at all the known frequencies. Then at least two conditions have to be fulfilled: (i) all predicted lines should have a counterpart in the observed spectrum with the right intensity and width - no single line should be missing; (ii) follow-up observations with interferometers have to prove whether all lines from the candidate species are emitted from the same spot. Given the chemical variety in hot core regions, this is a powerful constraint. Moreover, interferometer images tend to have less line confusion, since many lines that are blended in larger beam single-dish spectra arise from different locations or are emitted by an extended region that is spatially filtered out. Using an interferometer for aiding molecule identifications was pioneered by Snyder and collaborators who (mostly) used the Berkeley-Illinois-Maryland-Array (BIMA) to clearly identify a number of species in the Sgr B2(N) Large Molecule Heimat (see Sect. 1.1.2).

We carried out a complete line survey of the hot core regions Sgr B2(N) and (M) with the IRAM 30 m telescope at 3 mm, along with partial surveys at 2 and 1.3 mm. One of the overall goals of our survey was to better characterize the molecular content of both regions. It also allows searches for ``new'' species once we have identified the lines emitted by known molecules (including vibrationally and torsionally excited states). In particular, many complex molecules have enough lines in the covered frequency ranges to apply criterion (i) above. Once a species fulfils this criterion, interferometer measurements of selected lines can be made to check criterion (ii).

1.3 Amino acetonitrile

One of our target molecules was amino acetonitrile (NH2CH2CN), a molecule chemically related to glycine. Whether it is a precursor to the latter is under debate (see Sect. 4.3). Not many astronomical searches for amino acetonitrile have been reported in the literature. In his dissertation, Storey (1976) reported searches for the JKa,Kc = 211-212 and 101-000 transitions at 1350.5 and 9071.7 MHz, respectively with the Parkes 64 m telescope. On afterthought, the only chance of success for their observations would have been if amino acetonitrile existed on large spatial scales, similar to the molecules described in Sect. 1.1.1 (see Sect. 3.7 for further limits on extended amino acetonitrile emission). Recently, Wirström et al. (2007) reported unsuccessful searches of a number of mm-wavelength transitions of amino acetonitrile toward a number of hot cores.

Here, we report our detection of warm compact emission from amino acetonitrile in Sgr B2(N) with the IRAM 30 m telescope, the Plateau de Bure Interferometer (PdBI) and the Australia Telescope Compact Array (ATCA), and upper limits on cold, spatially extended emission from amino acetonitrile that we obtained with the NRAO Very Large Array (VLA). Section 2 summarizes the observational details. We present our results in Sect. 3. Implications in terms of interstellar chemistry are discussed in Sect. 4. Our conclusions are summarized in Sect. 5.

   
2 Observations and data reduction

   
2.1 Single-dish observations and data reduction

We carried out millimeter line observations with the IRAM 30 m telescope on Pico Veleta, Spain, in January 2004, September 2004 and January 2005. We used four SIS heterodyne receivers simultaneously, two in the 3 mm window connected to the autocorrelation spectrometer VESPA and two in the 1.3 mm window with filter banks as backends. A few selected frequency ranges were also observed with one SIS receiver at 2 mm in January 2004. The channel spacing and bandwidth were 0.313 and 420 MHz for each receiver at 3 and 2 mm, and 1 and 512 MHz for each receiver at 1.3 mm, respectively. The observations were done in single-sideband mode with sideband rejections of $\sim$1-3$\%$ at 3 mm, $\sim$5-7$\%$ at 2 mm, and $\sim$5-8$\%$ at 1.3 mm. The half-power beamwidths can be computed with the equation HPBW ( $\hbox{$^{\prime\prime}$ }$) = $\frac{2460}{\nu({\rm GHz})}$. The forward efficiencies $F_{{\rm eff}}$ were 0.95 at 3 mm, 0.93 at 2 mm, and 0.91 at 1.3 mm, respectively. The main-beam efficiencies were computed using the Ruze function $B_{{\rm eff}} = 1.2 \epsilon ~~ {\rm e}^{-(4 \pi R \sigma / \lambda)^2}$, with $\epsilon = 0.69$, $R \sigma = 0.07$, and $\lambda$ the wavelength in mm (see the IRAM 30 m telescope system summary on http://www.iram.es). The system temperatures ranged from 96 to 600 K at 3 mm, from 220 to 720 K at 2 mm (except at 176 GHz where they ranged from 2400 to 3000 K), and from 280 to 1200 K at 1.3 mm. The telescope pointing was checked every $\sim$1.5 h on Mercury, Mars, 1757-240 or G10.62, and found to be accurate to 2-3 $\hbox{$^{\prime\prime}$ }$ (rms). The telescope focus was optimized on Mercury, Jupiter, Mars or G34.3+0.2 every $\sim$1.5-3 h. The observations were performed toward both sources Sgr B2(N) ( $\alpha_{{\rm J2000}}$ = 17$^{\rm h}$47$^{\rm m}$20 $\hbox{$.\!\!^{\rm s}$ }$0, $\delta_{{\rm J2000}}$ = $-28^\circ$22 $\hbox{$^\prime$ }$19.0 $\hbox{$^{\prime\prime}$ }$, $V_{{\rm lsr}}$ = 64 km s-1) and Sgr B2(M) ( $\alpha_{{\rm J2000}}$ = 17$^{\rm h}$47$^{\rm m}$20 $\hbox{$.\!\!^{\rm s}$ }$4, $\delta_{{\rm J2000}}$ = $-28^\circ$23 $\hbox{$^\prime$ }$07.0 $\hbox{$^{\prime\prime}$ }$, $V_{{\rm lsr}}$ = 62 km s-1) in position-switching mode with a reference position offset by ( $\Delta\alpha$, $\Delta\delta$) = ( $-752\hbox{$^{\prime\prime}$ }$ $+342\hbox{$^{\prime\prime}$ }$) with respect to the former. The emission toward this reference position was found to be weak: $T_{{\rm a}}^\star$(12CO 1-0) $\sim$ 2 K, $T_{{\rm a}}^\star$(CS 2-1) $\la$ 0.05 K, $T_{{\rm a}}^\star$(12CO 2-1) $\sim$ 1.5 K, $T_{{\rm a}}^\star$(13CO 2-1) $\la$ 0.1 K, and it is negligible for higher excitation lines and/or complex species.

We observed the full 3 mm window between 80 and 116 GHz toward both sources. The step between two adjacent tuning frequencies was 395 MHz, which yielded an overlap of 50 MHz. The autocorrelator VESPA produces artificial spikes with a width of 3-5 channels at the junction between subbands (typically 2 or 3 spikes per spectrum). To get rid of these artefacts, half of the integration time at each tuning frequency was spent with the backend shifted by 50 MHz, so that we could, without any loss of information, systematically remove in each spectrum 5 channels at each of the 6 junctions between subbands that were possibly affected by this phenomenon. At 2 mm, we observed at only 8 selected frequencies, and removed the artificial spikes in the same way as at 3 mm. At 1 mm, we covered the frequency ranges 201.8 to 204.6 GHz and 205.0 to 217.7 GHz, plus a number of selected spots at higher frequency. For each individual spectrum, we removed a 0 ${{\rm th}}$-order (constant) baseline by selecting a group of channels which seemed to be free of emission or absorption. However, many spectra are full of lines, especially at 1.3 mm where we reached the confusion limit, and we may have overestimated the level of the baseline for some of them.

In $T_{{\rm a}}^\star$ scale, the rms noise level achieved towards Sgr B2(N) is about 15-20 mK below 100 GHz, 20-30 mK between 100 and 114.5 GHz, and about 50 mK between 114.5 and 116 GHz. At 1.3 mm, we reached the confusion limit for most of the spectra. The data were reduced with the CLASS software, which is part of the GILDAS software package (see http://www.iram.fr/IRAMFR/GILDAS).

   
2.2 Interferometric observations with the PdBI

We observed Sgr B2(N) with the PdBI for 4.7 h on February 7 ${{\rm th}}$, 2006 with 6 antennas in the high-resolution A configuration (E24E68E04N46W27N29). The coordinates of the phase center were $\alpha_{{\rm J2000}} = 17^{{\rm h}}47^{{\rm m}}20\hbox{$.\!\!^{\rm s}$ }00$, $\delta _{{\rm J2000}} = -28^\circ 22\hbox {$^\prime $ }19.0\hbox {$^{\prime \prime }$ }$. The 3 and 1.2 mm receivers were tuned to 81.982 and 245.380 GHz, respectively, in single side band mode. At 3 mm, there were two spectral windows centered at 81.736 and 82.228 GHz with a bandwidth of 80 MHz and a channel separation of 0.313 MHz, and two continuum windows of 320 MHz bandwidth centered at 81.852 and 82.112 GHz. The atmospheric phase stability was good for the 3 mm band but bad for the 1.2 mm band. Therefore we do not analyze the 1.2 mm data. The system temperatures were typically 150-220 K at 3 mm in the lower sideband. The (naturally-weighted) synthesized half-power beam width was $3.4\hbox{$^{\prime\prime}$ }$ $\times $ $0.8\hbox{$^{\prime\prime}$ }$ with PA 10$^\circ $, and the primary beam was $\sim$ $61\hbox{$^{\prime\prime}$ }$ FWHM. The correlator bandpass was calibrated on the quasar 3C 273. Phase calibration was determined on the nearby sources NRAO 530 and 1622-297. The time-dependent amplitude calibration was done on 1622-297, NRAO 530, 1334-127, and 1749+096, while the absolute flux density scale was derived from MWC 349. The absolute calibration uncertainty is estimated to be $\sim$15$\%$. The data were calibrated and imaged using the GILDAS software. The continuum emission was estimated on line-free portions of the bands and removed in the uv plane. The deconvolution was performed with the CLEAN method (Clark 1980).

   
2.3 Interferometric observations with the ATCA

We observed Sgr B2(N) with the ATCA on May 17 ${{\rm th}}$, 2006 in the hybrid H 214 configuration for 6 h, for 7 h on July 30 ${{\rm th}}$, 2006 in the H 168 configuration, and for 6 hours in the compact H 75 configuration on September 25 ${{\rm th}}$, 2006. The coordinates of the phase center were $\alpha_{{\rm J2000}} = 17^{{\rm h}}47^{{\rm m}}20\hbox{$.\!\!^{\rm s}$ }00$, $\delta _{{\rm J2000}} = -28^\circ 22\hbox {$^\prime $ }19.0\hbox {$^{\prime \prime }$ }$. The 3 mm receiver was alternately tuned to three frequency pairs of 90.550 and 93.200 GHz, 90.779 and 93.200 GHz, and 99.978 and 97.378 GHz in single side band mode, where only the first frequency of each pair was in spectral line mode with 32 MHz bandwidth and 128 channels. The second frequency of each pair was configured for continuum observations with 128 MHz bandwidth each. The system temperatures were typically 60 K. The (naturally-weighted) synthesized half-power beam width was $2.8\hbox{$^{\prime\prime}$ }$ $\times $ $1.9\hbox{$^{\prime\prime}$ }$ with PA $72^\circ$ for H 214, $3.9\hbox{$^{\prime\prime}$ }$ $\times $ $1.9\hbox{$^{\prime\prime}$ }$ with PA $-86^\circ$ for H 168, and $6.9\hbox{$^{\prime\prime}$ }$ $\times $ $5.4\hbox{$^{\prime\prime}$ }$ with PA $-73^\circ$ for H 75. The combination of H 214 and H 168 yields a synthesized half-power beam width of $3.0\hbox{$^{\prime\prime}$ }$ $\times $ $1.9\hbox{$^{\prime\prime}$ }$ with PA $82^\circ$, and the combination of all three configurations a synthesized half-power beam width of $3.4\hbox{$^{\prime\prime}$ }$ $\times $ $2.3\hbox{$^{\prime\prime}$ }$ with PA $83^\circ$. The primary beam was $\sim$ $2.4\hbox{$^\prime$ }$ FWHM. The correlator bandpass was calibrated on PKS 1253-055. The phase and gain calibration was determined on the nearby source PKS 1759-39. The absolute flux density scale was derived from Uranus. The absolute calibration uncertainty is estimated to be $\sim$20$\%$. The data were calibrated, continuum subtracted, imaged, and deconvolved using the software package MIRIAD (Sault et al. 1995).

Our ATCA data are affected by two problems. First, the tuning frequency used in May was not updated for the new observatory velocity in July and September. As a result, the observed bands were shifted by +12 and +16 MHz in rest frequency in the H 168 and H 75 configurations with respect to the H 214 configuration. Second, we suspect a technical problem with the tuning at 99 GHz in May and July because we do not detect any line in the H 214 and H 168 configurations while we easily detect two lines in the H 75 configuration: one unidentified line and one line from CH3CH3CO, $v_{{\rm t}}=1$ according to our line survey with the IRAM 30 m telescope. Comparing this band to the two other bands where we detect every line in each configuration (albeit with different intensities due to variable spatial filtering), we consider it to be very unlikely that the two lines detected at 99 GHz in the H 75 configuration are completely filtered out in the H 214 and H 168 configurations. Since the amino acetonitrile transition is shifted out of the H 75 band at 99 GHz (due to the variation of the observatory velocity), we do not analyze this dataset in the present article.

   
2.4 Interferometric observations with the VLA

We used the NRAO Very Large Array to search for the 101-000 multiplet of amino acetonitrile at 9071.208 MHz and examine the possibility of cold extended emission from this molecule. The VLA data were taken over a 1.5 h interval on February 13 ${{\rm th}}$, 2003 when the array was in its lowest-resolution (D) configuration. Three $\sim$20 min long scans of the following position in Sgr B2 were alternated with scans of the phase calibrator NRAO 530. For absolute flux density calibration, 3C 286 was observed. Our phase center in Sgr B2 was at $\alpha_{{\rm J2000}}$ = 17$^{\rm h}$47$^{\rm m}$20 $\hbox{$.\!\!^{\rm s}$ }$00, $\delta_{{\rm J2000}}$ = $-28^\circ$22 $\hbox{$^\prime$ }$51.0 $\hbox{$^{\prime\prime}$ }$. This is $32\hbox{$^{\prime\prime}$ }$ South and $16\hbox{$^{\prime\prime}$ }$ North of our 30 m telescope pointing positions for Sgr B2(N) and (M), respectively.

Our observations were done in spectral line mode with one intermediate frequency (IF) band split into 32 channels, each of which had a width of 0.1953 MHz, corresponding to 6.46 km s-1. The usable central 72$\%$ frequency range of the IF bandwidth, 4.49 MHz, covered all the multiplet's 7 hyperfine structure (hfs) components[*]. This frequency range corresponds to a total velocity coverage of 148 km s-1. The center velocity was set to $V_{{\rm lsr}}$ = 65 km s-1. A 4.49 MHz bandwidth ``pseudo continuum'' database (the so-called ``channel 0'') was created by averaging the central 23 channels. The uv-data were calibrated using the NRAO's Astronomical Imaging Processing System (AIPS). Several iterations of self calibration delivered a high quality continuum image. Using UVLIN, the average of selected regions of the line uv-database were subtracted channel by channel from the latter to remove the continuum level. To calibrate the spectral line data, the phase and amplitude corrections determined by the initial calibration, as well as by the self calibration were transferred to the line database and applied to them successively, producing a 23 channel database which was imaged channel by channel using natural weighting. The synthesized beam width of the images is $20.5\hbox{$^{\prime\prime}$ }$ $\times $ $7.0\hbox{$^{\prime\prime}$ }$ FWHM with a position angle of $-6.3^\circ$ East of North.

   
3 Identification of amino acetonitrile

   
3.1 Amino acetonitrile frequencies

In the course of the present investigation an amino acetonitrile entry (tag: 56507) has been prepared for the catalog of the Cologne Database for Molecular Spectroscopy (CDMS, see Müller et al. 2005,2001). The laboratory transition frequencies were summarized by Bogey et al. (1990). Their work included microwave transitions reported without 14N quadrupole splitting by MacDonald & Tyler (1972), Pickett (1973), as well as microwave transitions reported with quadrupole splitting by Brown et al. (1977); the latter data were used with the reported splitting. Line fitting and prediction of transition frequencies was done with the SPFIT/SPCAT suite of programs (Pickett 1991) using a Watson type Hamiltonian in the S reduction in the representation Ir (see, e.g., Gordy & Cook 1984).

The set of spectroscopic parameters reported by Bogey et al. (1990) included terms of up to decic order (SK), rather unusual for an apparently rigid and fairly heavy molecule, and we found the higher order parameters to be surprisingly large. Moreover, the off-diagonal sextic distortion parameter h3 was larger in magnitude than h2, and h1 was not even used in the fit; the importance of these parameters is reversed to what is more commonly found. Therefore, we performed a trial fit with the octic and decic parameters as well as h2 and h3 omitted and the sextic term HK fixed to a value that was estimated from $A/D_K \approx D_K/H_K$. Subsequently, we found that inclusion of h1 improved the quality of the fit. All transitions but five having $\Delta K_a \ge 1$ and $K''_a \ge 3$ could be reproduced well. Two of these had Ka = 3-2 and deviated $\sim$3.5 MHz from the predicted frequencies which was only twice the predicted uncertainty. The inclusion of these transitions in the fit caused relatively small changes in A and DK; changes in the remaining parameters were within the uncertainties. Therefore, it is likely that the assignments of these two transitions are correct. Effects on the predicted $\Delta K_a = 0$ transition frequencies are negligible. The remaining three transitions are considered to be mis-assignments as their inclusion would require many more higher order distortion parameters with apparently unphysical values and a poorer quality of the fit. Hence, those transitions were omitted from our fit. The resulting spectroscopic parameters are given in Table 1. The rotational partition function at 75 and 150 K is 4403 and 12 460, respectively.


  
Table 1: Spectroscopic parametersa (MHz) of amino acetonitrile.
\begin{displaymath}\begin{tabular}{lr@{}l}
\hline\hline
Parameter &\multicolumn{...
...) \\
$h_1 \times 10^9$ & 2&.989~(225) \\
\hline
\end{tabular}\end{displaymath}
(a) Watson's S-reduction was employed in the representation Ir. The dimensionless weighted rms of the fit is 0.51, therefore, the numbers in parentheses may be considered as two standard deviations in units of the least significant figures.
(b) Assumed value (see Sect. 3.1).

   
3.2 Modeling of the 30 m line survey

The average line density above 3$\sigma $ in our 30 m survey is about 100 and 25 features per GHz for Sgr B2(N) and (M), respectively, translating into about 3700 and 950 lines over the whole 80-116 GHz band. To identify a new molecule in such a line forest and reduce the risk of mis-assignments, it is essential to model first the emission of all known molecules, including vibrationally and torsionally excited states, and their isotopologues. We used the XCLASS software (see Comito et al. 2005, and references therein) to model the emission and absorption lines in the LTE approximation. These calculations take into account the beam dilution, the line opacity, and the line blending. The molecular spectroscopic parameters are taken from our line catalog which contains all entries from the CDMS catalog (Müller et al. 2005,2001) and from the molecular spectroscopic database of the Jet Propulsion Laboratory (JPL, see Pickett et al. 1998), plus additional ``private'' entries.

Each molecule is modeled separately with the following set of input parameters: source size, rotational temperature, column density, velocity linewidth, velocity offset with respect to the systemic velocity of the source, and a flag indicating if it is an emission or absorption component. For some of the molecules, it was necessary to include several velocity components to reproduce the observed spectra. The velocity components in emission are supposed to be non-interacting, i.e. the intensities add up linearly. The radiative transfer is computed in the following way: first the emission line spectrum is calculated, and then the absorption lines, using the full (lines + continuum) emission spectrum as background to absorb against. The vibrationally and/or torsionally excited states of some molecules were modeled separately from the ground state. The input parameters were varied until a good fit to the data was obtained for each molecule. The whole spectrum including all the identified molecules was then computed at once, and the parameters for each molecule were adjusted again when necessary. The quality of the fit was checked by eye over the whole frequency coverage of the line survey. We favored our eye-checking method against an automated fitting because the high occurence of line blending and the uncertainty in the baseline removal would in many cases make an automated fitting procedure fail.

The detailed results of this modeling will be published in a forthcoming article describing the complete survey (Belloche et al., in prep.). So far, we have identified 51 different molecules, 60 isotopologues, and 41 vibrationally/torsionally excited states in Sgr B2(N), which represent about 60$\%$ of the lines detected above the 3$\sigma $ level. In Sgr B2(M), the corresponding numbers are 41, 50, 20, and 50$\%$, respectively.

   
3.3 Detection of amino acetonitrile with the 30 m telescope


 

 
Table 3: Transitions of amino acetonitrile detected toward Sgr B2(N) with the IRAM 30 m telescope.
Na Transition Frequency Unc.b $E_{\rm l}^c$ $S\mu ^2$ $\sigma^d$ Fe $\tau^f$ $I_{{\rm obs}}^g$ $I_{{\rm AAN}}^g$ $I_{{\rm all}}^g$ Comments
    (MHz) (kHz) (K) (D2) (mK)     (K km s-1) (K km s-1) (K km s-1)  
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13)
1 9 0, 9-8 0, 8 80 947.479 7 16 60 33 1 0.13 0.65(16) 0.38 0.42 no blend
3 9 5, 5-8 5, 4 81 700.966 6 47 41 13 2 0.16 0.92(07) 0.67 0.75 partial blend with U-line
4 9 5, 4-8 5, 3 81 700.967 6 47 41 13 2 - - - - -
5 9 6, 3-8 6, 2 81 702.498 5 60 33 13 2 - - - - -
6 9 6, 4-8 6, 3 81 702.498 5 60 33 13 2 - - - - -
7 9 4, 6-8 4, 5 81 709.838 6 35 48 13 3 0.23 0.39(06) 0.66 0.73 no blend
8 9 7, 2-8 7, 1 81 709.848 6 76 24 13 3 - - - - -
9 9 7, 3-8 7, 2 81 709.848 6 76 24 13 3 - - - - -
10 9 4, 5-8 4, 4 81 710.098 6 35 48 13 3 - - - - -
11 9 3, 7-8 3, 6 81 733.892 6 27 53 13 4 0.11 0.50(06) 0.32 1.46 blend with CH3OCH3 and
                        HCC13CN, v6 = 1
12 9 3, 6-8 3, 5 81 756.174 6 27 53 13 5 0.11 0.39(06) 0.32 0.32 blend with U-line
13 9 2, 7-8 2, 6 82 224.644 7 21 57 19 6 0.12 0.19(08) 0.36 0.35 uncertain baseline
17 10 2, 9-9 2, 8 90 561.332 6 25 64 20 7 0.14 0.64(09) 0.52 1.01 blend with weak
                        C2H5CN, v13 = 1/v21 = 1
18 10 6, 4-9 6, 3 90 783.538 6 64 43 14 8 0.28 1.54(06) 1.05 1.40 partial blend with CH2(OH)CHO and
                        U-line
19 10 6, 5-9 6, 4 90 783.538 6 64 43 14 8 - - - - -
20 10 5, 6-9 5, 5 90 784.281 6 50 50 14 8 - - - - -
21 10 5, 5-9 5, 4 90 784.285 6 50 50 14 8 - - - - -
22 10 7, 3-9 7, 2 90 790.259 6 80 34 14 9 0.09 0.51(06) 0.33 0.56 blend with U-line
23 10 7, 4-9 7, 3 90 790.259 6 80 34 14 9 - - - - -
24 10 4, 7-9 4, 6 90 798.685 6 39 56 14 10 0.21 1.42(06) 0.81 0.95 blend with U-line
25 10 4, 6-9 4, 5 90 799.249 6 39 56 14 10 - - - - -
28 10 3, 8-9 3, 7 90 829.945 6 31 60 14 11 0.13 0.84(06) 0.47 0.51 blend with U-line also in M?
29 10 3, 7-9 3, 6 90 868.038 6 31 60 14 12 0.13 0.49(06) 0.47 0.57 partial blend with U-line
30 10 2, 8-9 2, 7 91 496.108 8 25 64 24 13 0.15 0.86(11) 0.53 0.71 partial blend with CH3CN, v4 = 1 and
                        U-line
32 11 1,11-10 1,10 97 015.224 8 25 72 21 14 0.18 2.05(09) 0.71 1.78 partial blend with C2H5OH and
                        CH3OCHO
47 11 3, 9-10 3, 8 99 928.886 6 35 68 14 15 0.15 1.31(06) 0.66 1.24 partial blend with NH2CN and U-line
48 11 3, 8-10 3, 7 99 990.567 7 35 68 14 16 0.15 0.80(06) 0.66 0.74 no blend
49 11 2, 9-10 2, 8 100 800.876 8 29 71 20 17 0.17 1.38(08) 0.75 1.25 partial blend with CH3CH3CO, v= 0
                        and U-line
50 11 1,10-10 1, 9 101 899.795 8 26 72 34 18 0.18 0.56(14) 0.81 0.88 uncertain baseline
51 12 1,12-11 1,11 105 777.991 8 29 79 43 19 0.20 1.98(18) 0.95 2.88 blend with c-C2H4O and
                        C2H5CN, v= 0
52 12 0,12-11 0,11 107 283.142 8 29 80 24 20 0.21 2.67(10) 1.00 2.01 blend with C2H5OH and U-line
53 12 2,11-11 2,10 108 581.408 7 34 77 20 21 0.19 1.49(08) 0.97 1.94 weak blend with C2H5OH
58 12 5, 8-11 5, 7 108 956.206 6 60 66 29 22 0.26 2.19(11) 1.34 3.44 blend with C2H5OH
59 12 5, 7-11 5, 6 108 956.229 6 60 66 29 22 - - - - -
68 12 3,10-11 3, 9 109 030.225 6 40 75 29 23 0.18 1.67(11) 0.89 1.24 partial blend with HC3N, v4 = 1,
                        C2H5OH, and U-line
71 12 1,11-11 1,10 111 076.901 8 31 79 25 24 0.21 1.16(10) 1.08 1.39 slightly shifted?
72 13 1,13-12 1,12 114 528.654 8 34 86 37 25 0.23 2.49(15) 1.23 1.42 partial blend with U-line
84 1510, 5-1410, 4 136 248.969 10 169 55 28 26 0.09 2.10(10) 0.72 1.03 blend with U-line
85 1510, 6-1410, 5 136 248.969 10 169 55 28 26 - - - - -
89 15 4,11-14 4,10 136 303.599 6 65 93 28 27 0.21 3.99(09) 1.62 4.02 blend with a(CH2OH)2 and CH3C3N
92 15 3,13-14 3,12 136 341.155 6 57 96 28 28 0.24 2.92(10) 1.81 2.22 partial blend with U-line also in M
103 16 5,12-15 5,11 145 325.871 30 83 96 25 29 0.39 2.89(08) 3.30 4.80 uncertain baseline, partial blend
                        with C2H5CN, v13 = 1/v21 = 1
104 16 5,11-15 5,10 145 326.209 30 83 96 25 29 - - - - -
105 1610, 6-1510, 5 145 330.985 40 175 65 25 30 0.11 0.97(07) 0.92 1.02 uncertain baseline
106 1610, 7-1510, 6 145 330.985 40 175 65 25 30 - - - - -
115 16 3,14-15 3,13 145 443.850 30 63 103 25 31 0.25 4.33(08) 2.18 4.68 blend with C2H5CN, v= 0 and
                        U-line
118 16 1,15-15 1,14 147 495.789 6 55 106 31 32 0.29 3.27(11) 2.54 11.47 partial blend with H3C13CN, v8 = 1
139 17 4,13-16 4,12 154 542.406 5 79 107 112 33 0.44 13.25(42) 4.63 5.52 blend with U-line
140 17 3,15-16 3,14 154 544.046 5 70 109 112 33 - - - - -
145 18 7,12-17 7,11 163 454.794 5 127 101 38 34 0.49 10.38(13) 5.32 16.48 partial blend with HC13CCN,
                        v6 = 1 and HCC13CN, v6 = 1
146 18 7,11-17 7,10 163 454.794 5 127 101 38 34 - - - - -
147 18 8,10-17 8, 9 163 456.136 6 146 96 38 34 - - - - -
148 18 8,11-17 8,10 163 456.136 6 146 96 38 34 - - - - -
149 18 9, 9-17 9, 8 163 470.472 8 166 90 38 35 0.41 15.17(14) 5.57 21.97 partial blend with HCC13CN,v7 = 1
150 18 9,10-17 9, 9 163 470.472 8 166 90 38 35 - - - - -
151 18 6,13-17 6,12 163 473.305 5 111 106 38 35 - - - - -
152 18 6,12-17 6,11 163 473.321 5 111 106 38 35 - - - - -
155 1811, 7-1711, 6 163 525.533 11 216 75 38 36 0.49 10.26(13) 5.27 17.96 blend with HC3N, v4 = 1
156 1811, 8-1711, 7 163 525.533 11 216 75 38 36 - - - - -
157 18 5,14-17 5,13 163 526.183 4 97 110 38 36 - - - - -
158 18 5,13-17 5,12 163 527.171 4 97 110 38 36 - - - - -
163 18 4,15-17 4,14 163 635.326 5 86 114 38 37 0.25 4.08(11) 2.82 5.01 partial blend with C3H7CN
164 18 3,16-17 3,15 163 640.468 5 78 116 38 38 0.28 4.65(11) 2.99 6.77 partial blend with C3H7CN
177 19 6,14-18 6,13 172 566.092 50 119 114 44 39 0.38 10.01(14) 4.39 6.43 partial blend with U-line and
                        HCC13CN, v7 = 1
178 19 6,13-18 6,12 172 566.092 50 119 114 44 39 - - - - -
227 23 4,20-22 4,19 209 272.189 6 130 148 58 40 0.26 7.29(29) 4.62 14.85 blend CH3CH3CO, v= 0
237 23 1,22-22 1,21 209 629.913 9 113 152 45 41 0.32 9.03(24) 5.54 30.88 blend with HC13CCN, v7 = 2 and
                        HCC13CN, v7 = 2
247 25 9,16-24 9,15 227 040.487 50 230 145 96 42 0.29 9.58(55) 9.45 35.33 partial blend with CN absorption
                        and CH3CH3CO, $v_{{\rm t}}$ = 1
248 25 9,17-24 9,16 227 040.487 50 230 145 96 42 - - - - -
249 25 8,18-24 8,17 227 045.287 50 210 149 96 42 - - - - -
250 25 8,17-24 8,16 227 045.287 50 210 149 96 42 - - - - -
251 2510,15-2410,14 227 055.944 50 254 139 96 43 0.15 -0.64(44) 3.29 3.62 partial blend with CN absorption
252 2510,16-2410,15 227 055.944 50 254 139 96 43 - - - - -
253 25 7,19-24 7,18 227 079.847 50 191 153 96 44 0.32 10.94(44) 7.16 57.69 blend with CH2CH13CN and
                        CH3OH, v= 0
254 25 7,18-24 7,17 227 079.847 50 191 153 96 44 - - - - -
273 25 2,23-24 2,22 231 485.527 50 138 165 40 45 0.30 12.73(19) 6.27 6.60 blend with U-line?
292 26 6,21-25 6,20 236 269.491 60 186 163 37 46 0.36 15.53(18) 8.02 14.17 partial blend with t-C2H5OCHO
                        and U-line
293 26 6,20-25 6,19 236 270.459 60 186 163 37 46 - - - - -
306 28 0,28-27 0,27 244 765.968 21 160 186 39 47 0.28 9.56(19) 6.62 10.35 blend with CH313CH2CN, v= 0
                        and U-line
322 27 6,22-26 6,21 245 378.722 10 197 170 72 48 0.35 16.69(36) 8.29 22.21 blend with 13CH3CH2CN, v= 0?
323 27 6,21-26 6,20 245 380.146 10 197 170 72 48 - - - - -
368 29 9,20-28 9,19 263 364.923 22 277 174 74 49 0.26 6.72(37) 8.51 9.17 baseline problem?, blend with
                        U-line
369 29 9,21-28 9,20 263 364.923 22 277 174 74 49 - - - - -
370 2910,19-2810,18 263 368.355 26 300 170 74 49 - - - - -
371 2910,20-2810,19 263 368.355 26 300 170 74 49 - - - - -
384 29 6,24-28 6,23 263 604.573 12 221 184 74 50 0.28 10.29(36) 8.81 14.22 baseline problem?, partial blend
                        with CH3CH3CO, $v_{{\rm t}}$ = 1 and
                        CH3OCH3
385 29 6,23-28 6,22 263 607.689 12 221 184 74 50 - - - - -
398 29 4,26-28 4,25 264 055.836 13 197 189 108 51 0.22 18.36(49) 5.92 14.22 partial blend with C2H5CN, v= 0
                        and CH3CH3CO, v= 0
Notes: a Numbering of the observed transitions with $S\mu ^2$ > 20 D2 (see Table 2). b Frequency uncertainty. c Lower energy level in temperature units ( $E_{\rm l}/$$k_{\rm B}$). d Calculated rms noise level in $T_{{\rm mb}}$ scale. e Numbering of the observed features. f Peak opacity of the amino acetonitrile modeled feature. g Integrated intensity in $T_{{\rm mb}}$ scale for the observed spectrum (Col. 10), the amino acetonitrile model (Col. 11), and the model including all molecules (Col. 12). The uncertainty in Col. 10 is given in parentheses in units of the last digit.


We consider it essential for claiming a detection of a new molecule that all lines of this molecule in our observed bands are consistent with this claim, i.e. are either detected or blended with lines of other species. Therefore, in the following, we inspect all transitions of amino acetonitrile in our frequency range. Our line survey at 3, 2, and 1.3 mm covers 596 transitions of our amino acetonitrile catalog (v= 0 only). Our LTE modeling shows, however, that the transitions with the line strength times the appropriate (a- or b-type) dipole moment squared, $S\mu ^2$, smaller than 20 D2 are much too weak to be detectable with the sensitivity we achieved. Therefore, we list in Table 2 (online material) only the 398 transitions above this threshold. To save some space, when two transitions have a frequency difference smaller than 0.1 MHz which cannot be resolved, we list only the first one. We number the transitions in Col. 1 and give their quantum numbers in Col. 2. The frequencies, the frequency uncertainties, the energies of the lower levels in temperature units, and the $S\mu ^2$ values are listed in Cols. 3-6, respectively. Since the spectra are in most cases close to the line confusion limit and it is difficult to measure the noise level, we give in Col. 7 the rms sensitivity computed from the system temperature and the integration time: $\sigma = \frac{F_{{\rm eff}}}{B_{{\rm eff}}} \times
\frac{2~T_{{\rm sys}}}{\sqrt{\delta f ~ t}}$, with $F_{{\rm eff}}$ and $B_{{\rm eff}}$ the forward and beam efficiencies, $T_{{\rm sys}}$ the system temperature, $\delta f$ the spectral resolution, and t the total integration time (on-source plus off-source).

We list in Col. 8 of Table 2 comments about the blends affecting the amino acetonitrile transitions. As can be seen in this table, most of the amino acetonitrile lines covered by our survey of Sgr B2(N) are heavily blended with lines of other molecules and therefore cannot be identified in this source. Only 88 of the 398 transitions are relatively free of contamination from other molecules, known or still unidentified according to our modeling. They are marked ``Detected'' or ``Group detected'' in Col. 8 of Table 2, and are listed with more information in Table 3. They correspond to 51 observed features which are shown in Fig. 1 (online material) and labeled in Col. 8 of Table 3. For reference, we show the spectrum observed toward Sgr B2(M) in this figure also. We identified the amino acetonitrile lines and the blends affecting them with the LTE model of this molecule and the LTE model including all molecules (see Sect. 3.2). The parameters of our best-fit LTE model of amino acetonitrile are listed in Table 4, and the model is overlaid in red on the spectrum observed toward Sgr B2(N) in Fig. 1. The best-fit LTE model including all molecules is shown in green in the same figure. The source size we used to model the amino acetonitrile emission was derived from our interferometric measurements (see Sect. 3.4 below).

For the frequency range corresponding to each observed amino acetonitrile feature, we list in Table 3 the integrated intensities of the observed spectrum (Col. 10), of the best-fit model of amino acetonitrile (Col. 11), and of the best-fit model including all molecules (Col. 12). In these columns, the dash symbol indicates transitions belonging to the same feature. Columns 1 to 7 are the same as in Table 2. The $1 \sigma $ uncertainty given in Col. 10 was computed using the estimated noise level of Col. 7. These measurements are plotted in the form of a population diagram in Fig. 2, which plots upper level column density divided by statistical weight, $N_{\rm u}/g_{\rm u}$, versus the upper level energy in Kelvins (see Goldsmith & Langer 1999). The data are shown in black and our best-fit model of amino acetonitrile in red. Out of 21 features encompassing several transitions, 10 contain transitions with different energy levels and were ignored in the population diagram (features 2, 3, 8, 33, 34, 35, 36, 42, and 49). We used Eq. (A5) of Snyder et al. (2005) to compute the ordinate values. This equation assumes optically thin emission. To estimate by how much line opacities affect this diagram, we applied the opacity correction factor $C_\tau = \frac{\tau}{1-{\rm e}^{-\tau}}$ (see Snyder et al. 2005; Goldsmith & Langer 1999) to the modeled intensities, using the opacities from our radiative transfer calculations (Col. 9 of Table 3); the result is shown in green in Fig. 2. The population diagram derived from the modeled spectrum is slightly shifted upwards but its shape, in particular its slope (the inverse of which approximately determines the rotation temperature), is not significantly changed, since ${\rm ln}~ C_{\tau}$ does not vary much (from 0.04 to 0.24). The populations derived from the observed spectrum in the optically thin approximation are therefore not significantly affected by the optical depth of the amino acetonitrile transitions[*]. The scatter of the black crosses in Fig. 2 is therefore dominated by the blends with other molecules and uncertainties in the baseline removal (indicated by the downwards and upwards blue arrows, respectively). From this analysis, we conclude that our best-fit model for amino acetonitrile is fully consistent with our 30 m data of Sgr B2(N).


  \begin{figure}
\par\includegraphics[angle=270,width=9cm,clip]{9203f2.eps}\end{figure} Figure 2: Population diagram of amino acetonitrile in Sgr B2(N). The red points were computed in the optically thin approximation using the integrated intensities of our best-fit model of amino acetonitrile, while the green points were corrected for the opacity. The black points were computed in the optically thin approximation using the integrated intensities of the spectrum observed with the IRAM 30 m telescope. The error bars are $1 \sigma $ uncertainties on $N_{\rm u}/g_{\rm u}$. Blue arrows pointing downwards mark the transitions blended with transitions from other molecules, while blue arrows pointing upwards indicate that the baseline removed in the observed spectrum is uncertain. The arrow length is arbitrary. The measurement corresponding to feature 43 (at $E_{\rm u}/k_{\rm B}$ = 265 K) is not shown since the integrated intensity measured toward Sgr B2(N) is negative, due to the blend with CN absorption lines.

Finally, as mentioned above, the 310 transitions of Table 2 not shown in Fig. 1 are all but one heavily blended with transitions of other molecules and cannot be clearly identified in Sgr B2(N). The single exception is amino acetonitrile transition 192 shown in Fig. 3. There are too many blended lines in this frequency range to properly remove the baseline. It is very uncertain and the true baseline is most likely at a lower level than computed here. The presence of several H13CN 2-1 velocity components in absorption also complicates the analysis. Therefore it is very likely that the (single) apparent disagreement concerning transition 192 between our best-fit model and the 30 m spectrum observed toward Sgr B2(N) is not real and does not invalidate our claim of detection of amino acetonitrile.


  \begin{figure}
\par\includegraphics[angle=270,width=9cm,clip]{9203f3.eps}\end{figure} Figure 3: Spectrum obtained toward Sgr B2(N) ( bottom) and Sgr B2(M) ( top) with the IRAM 30 m telescope at the frequency of amino acetonitrile (AAN) transition 192 (see caption of Fig. 1 for more details about the color coding). There are too many blended lines in the spectrum of Sgr B2(N) to properly remove the baseline, which is very uncertain and most likely at a lower level than could be computed here. This is the only discrepancy concerning the amino acetonitrile lines in the whole survey. The absorption lines, particularly strong in the spectrum of Sgr B2(M), are velocity components of H13CN 2-1.

   
3.4 Mapping amino acetonitrile with the PdBI

The two 3 mm spectral windows of the PdBI were chosen to cover the five amino acetonitrile features F2 to F6. The spectra toward Sgr B2(N) are shown for both windows toward 3 positions P1, P2, and P3 in Figs. 4a to f. Many lines are detected, the strongest one being a line from within the vibrationally excited state v7 = 1 of cyanoacetylene (HC3N) at 82.2 GHz. We also easily detect lines from within its vibrationally excited state v4 = 1, from its isotopologues HC13CCN and HCC13CN in the v7 = 1 state, from ethyl cyanide (C2H5CN), as well as two unidentified lines at 82.213 and 82.262 GHz. At a lower level, we find emission for all the amino acetonitrile features F2 to F6, and we also detect methylformate (CH3OCHO).


   
Table 4: Parameters of our best-fit LTE model of amino acetonitrile.
Sizea $T_{{\rm rot}}$ $N_{{\rm AAN}}$b FWHM $V_{{\rm off}}$c
('') (K) (cm-2) (km s-1) (km s-1)
(1) (2) (3) (4) (5)
2.0 100 $ 2.80 \times 10^{16}$ 7.0 0.0
a Source diameter (FWHM).
b Column density of amino acetonitrile.
c Velocity offset with respect to the systemic velocity of Sgr B2(N) $V_{{\rm lsr}} = 64$ km s-1.


 

 
Table 5: Measurements obtained toward Sgr B2(N) with the IRAM Plateau de Bure interferometer at 82 GHz.
Molecule Fa $f_{{\rm min}}$b $f_{{\rm max}}$b $\sigma^c$ $F_{{\rm peak}}$d $\Delta\alpha$d $\Delta\delta$d $\theta_{{\rm maj}}^{{fwhm}}$ d $\theta_{{\rm min}}^{{fwhm}}$ d PAd $\Phi_{{\rm PdBI}}^e$ $\Phi_{{\rm 30~m}}^f$
    (MHz)) (MHz) (Jy/beam km s-1) ('') ('') ('') ('') ($^\circ $) (Jy km s-1) (Jy km s-1)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13)
AAN F2 81 700.21 81 703.33 0.09 0.68 -1.60 $\pm$ 0.05 0.30 $\pm$ 0.22 3.9 $\pm$ 0.4 2.00 $\pm$ 0.10 20.5 $\pm$ 0.1 1.76 2.89
AAN F3 81 708.02 81 712.08 0.10 0.68 -1.25 $\pm$ 0.06 0.02 $\pm$ 0.24 3.8 $\pm$ 0.5 1.39 $\pm$ 0.12 10.1 $\pm$ 0.0 1.24 1.75
AAN F4 81 732.71 81 734.90 0.06 0.44 -1.70 $\pm$ 0.06 0.35 $\pm$ 0.24 3.6 $\pm$ 0.5 1.54 $\pm$ 0.12 14.0 $\pm$ 0.0 0.86 0.98
AAN F5 81 754.90 81 757.40 0.06 0.24 -1.52 $\pm$ 0.10 0.03 $\pm$ 0.44 3.2 $\pm$ 0.9 1.20 $\pm$ 0.21 12.5 $\pm$ 1.1 0.30 1.15
AAN F6 82 223.46 82 226.27 0.06 0.43 -1.43 $\pm$ 0.06 0.28 $\pm$ 0.24 3.5 $\pm$ 0.5 1.54 $\pm$ 0.11 6.0 $\pm$ 0.4 0.79 0.97
Reference   81 704.27 81 707.08 0.07 ... ... ... ... ... ... ... ...
C2H5CN HV 81 741.77 81 744.90 0.11 2.05 -1.64 $\pm$ 0.02 5.58 $\pm$ 0.09 3.8 $\pm$ 0.2 1.50 $\pm$ 0.04 5.7 $\pm$ 0.0 4.07 6.38
C2H5CN LV 81 745.21 81 749.27 0.15 2.82 -1.74 $\pm$ 0.02 0.46 $\pm$ 0.09 3.8 $\pm$ 0.2 2.87 $\pm$ 0.04 13.7 $\pm$ 0.0 10.43 12.94
HC13CCN v7=1   81 726.15 81 728.96 0.09 2.20 -1.35 $\pm$ 0.02 0.60 $\pm$ 0.07 3.7 $\pm$ 0.1 1.68 $\pm$ 0.03 12.6 $\pm$ 0.0 4.98 4.81
HC3N v4=1   81 767.71 81 771.15 0.10 2.14 -1.43 $\pm$ 0.02 0.28 $\pm$ 0.08 3.6 $\pm$ 0.2 1.35 $\pm$ 0.04 9.9 $\pm$ 0.0 3.78 3.85
HC3N v7=1g HV 82 196.27 82 198.77 0.25 6.17 -2.16 $\pm$ 0.02 0.69 $\pm$ 0.07 4.0 $\pm$ 0.1 1.84 $\pm$ 0.03 16.2 $\pm$ 22.5 16.05 23.88
          3.36 -1.50 $\pm$ 0.03 5.25 $\pm$ 0.12 4.0 $\pm$ 0.2 1.36 $\pm$ 0.06 5.5 $\pm$ 22.5 5.35 ...
HC3N v7=1 LV 82 199.40 82 201.58 0.36 9.06 -1.67 $\pm$ 0.02 0.42 $\pm$ 0.07 3.7 $\pm$ 0.1 2.50 $\pm$ 0.03 10.2 $\pm$ 22.5 31.04 33.48
HC3N v7=1 BW 82 202.52 82 203.77 0.12 3.37 -0.71 $\pm$ 0.01 0.24 $\pm$ 0.06 3.1 $\pm$ 0.1 2.77 $\pm$ 0.03 45.0 $\pm$ 0.0 11.75 12.39
CH3OCHO   82 242.21 82 245.33 0.10 0.67 -2.83 $\pm$ 0.06 1.23 $\pm$ 0.26 4.8 $\pm$ 0.5 2.58 $\pm$ 0.12 9.5 $\pm$ 22.5 2.83 6.62
a Feature numbered like in Col. 8 of Table 3 for amino acetonitrile (AAN). HV and LV mean ``high'' and ``low'' velocity components, respectively, and BW means blueshifted linewing.
b Frequency range over which the intensity was integrated.
c Noise level in the integrated intensity map shown in Fig. 5.
d Peak flux, offsets in right ascension and declination with respect to the reference position of Fig. 5, major and minor diameters (FWHM), and position angle (East from North) derived by fitting an elliptical 2D Gaussian to the integrated intensity map shown in Fig. 5. The uncertainty in Col. 11 is the formal uncertainty given by the fitting routine GAUSS_2D, while the uncertainties correspond to the beam size divided by two times the signal-to-noise ratio in Cols. 7 and 8 and by the signal-to-noise ratio in Cols. 9 and 10.
e Flux spatially integrated over the region showing emission in the integrated intensity map of Fig. 5.
f Integrated flux of the 30 m spectrum computed over the frequency range given in Cols. 3 and 4.
g The two emission peaks of Fig. 5k were fitted separately.


The integrated intensity maps of the amino acetonitrile features F2 to F6 are presented in Figs. 5a to e, along with two maps of ethyl cyanide (Figs. 5g and h), four maps of cyanoacetylene in the vibrationally excited states v4 = 1 and v7 = 1 (Figs. 5j to m), one map of its isotopologue HC13CCN in the state v7 = 1 (Fig. 5i), one map of methylformate (Fig. 5n), and a reference map computed on the PdBI line-free frequency range between F2 and F3 (Fig. 5f). The frequency intervals used to compute the integrated intensities are given in Cols. 3 and 4 of Table 5 and shown with dotted lines in Fig. 4. We used the fitting routine GAUSS_2D of the GILDAS software to measure the position, size, and peak flux of each integrated emission. The results are listed in Cols. 6 to 11 in Table 5. We label P1 the mean peak position of features F2 to F6, P2 the northern peak position of ethyl cyanide, and P3 the peak position of methylformate (see Table 6 and the plus symbols in Fig. 5). Finally, the PdBI velocity-integrated flux spatially integrated over the emitting region is listed in Col. 12 and the 30 m velocity-integrated intensity is given in Col. 13.


  \begin{figure}
\par\includegraphics[angle=270,width=8.9cm,clip]{9203f4.eps}\end{figure} Figure 4: Spectra obtained with the Plateau de Bure interferometer (a) to f)) and the 30 m telescope (g) and h)) toward Sgr B2(N) (in black). The dotted lines show the frequency ranges listed in Table 5. The offset position with respect to the reference position of Fig. 5 is given in each panel, along with a label (P1 to P3, see their definition in Table 6). The lines identified in our 30 m survey are labeled in blue. The red spectra show our best-fit model for amino acetonitrile (AAN) while the green spectrum corresponds to the 30 m model including all molecules. The observed lines which have no counterpart in the green spectrum are still unidentified.

We present in Fig. 5o the map of continuum emission at 82.0 GHz, integrated over line-free frequency ranges. The continuum emission has a complex structure. The main region peaks at $\alpha_{{\rm J2000}} = 17^{{\rm h}}47^{{\rm m}}19\hbox{$.\!\!^{\rm s}$ }886 \pm 0\hbox{$.\!\!^{\rm s}$ }005$, $\delta_{{\rm J2000}} = -28^\circ22\hbox{$^\prime$ }18.4\hbox{$^{\prime\prime}$ }\pm 0.1\hbox{$^{\prime\prime}$ }$, i.e. within 0.1 $\hbox{$^{\prime\prime}$ }$ of the position of the ultracompact H II region K2. It also shows hints of emission at the position of the ultracompact H II regions K1 and K3, although the spatial resolution is too poor to resolve them (see, e.g., Gaume et al. 1995). There are other secondary peaks. One of them coincides with the peak of the shell-like H II region K6 while another one is located close (< $2\hbox{$^{\prime\prime}$ }$) to the peak of the shell-like H II region K5 and traces most likely the same shell. On the other hand, we detect no 3.7 mm emission at the position of the weak ultracompact H II region K9.69 (Gaume et al. 1995).


  \begin{figure}
\par\includegraphics[height=18.4cm,angle=-90,clip]{NEWFIG5/9203f5.eps}\end{figure} Figure 5: Integrated intensity maps (panels a) to n)) and continuum map (panel o)) obtained toward Sgr B2(N) with the Plateau de Bure interferometer at 82 GHz. Panels a) to e) show the amino acetonitrile (AAN) features F2 to F6 (see Fig. 4 and Table 3). Panel f) is a reference map integrated on the emission-free frequency range between F2 and F3. Panels g) to n) show the other molecules listed in Table 5. The lowest contour (positive in black solid line and negative in blue dotted line) and the contour step are 2$\sigma $ for panel f), 3$\sigma $ for panels a) to e) and panel n), 4$\sigma $ for panels g) and h), 5$\sigma $ for panels i) to l), and 6$\sigma $ for panel m) (with $\sigma $ given in Col. 5 of Table 5). For panel o), the first contours are 5$\sigma $ and 10$\sigma $, and the contour step is 10$\sigma $ for the other contours (with $\sigma $ = 8.5 mJy/beam). In each panel, the 0, 0 position is $\alpha_{{\rm J2000}} = 17^{{\rm h}}47^{{\rm m}}20\hbox{$.\!\!^{\rm s}$ }00$, $\delta _{{\rm J2000}} = -28^\circ 22\hbox {$^\prime $ }19.0\hbox {$^{\prime \prime }$ }$, the three plus symbols mark the positions P1, P2, and P3 (labeled in panel f)), and the filled ellipse in the top right corner shows the clean beam ( HPBW = $3.35\hbox {$^{\prime \prime }$ }$ $\times $ $0.81\hbox {$^{\prime \prime }$ }$ at PA = 9.7$^\circ $). The cross symbols in panel o) are the peak positions of the (ultracompact) H II regions detected by Gaume et al. (1995) at 1.3 cm (K9.69, K1, K2, K3, K5, and K6, from right to left). The spectral integration was done on the frequency ranges given in Table 5. The continuum map was computed on line-free frequency ranges. The maps are not corrected for primary beam attenuation. The amino acetonitrile features emit at the same position as the vibrationally excited state v4 = 1 of cyanoacetylene. Feature F4 is partially blended with a transition from HCC13CN, v6 = 1.

The strong lines detected with the PdBI (Figs. 5g to n) allow us to gain insight into the distribution of molecular line emission in Sgr B2(N). The double-peaked profile of ethyl cyanide seen with the 30 m telescope (see Fig. 4g) is resolved with the PdBI into two sources P1 and P2 separated by about 5.3 $\hbox{$^{\prime\prime}$ }$ (see Figs. 4a, c, g, h, and Table 6). P1 and P2 are spatially and kinematically coincident with the quasi-thermal methanol emission cores ``i'' and ``h'' within $0.6\hbox{$^{\prime\prime}$ }$ and $0.2\hbox{$^{\prime\prime}$ }$, respectively (Mehringer & Menten 1997). Cores ``i'' and ``h'' were both previously detected in ethyl cyanide (Jones et al. 2007; Liu & Snyder 1999; Hollis et al. 2003). Many molecules (but not amino acetonitrile within the limits of our sensitivity) actually show this double-peaked profile in our 30 m survey of Sgr B2(N) and are most likely emitted by these two sources. P1 and P2 are also detected in our PdBI data in the vibrationally excited state v7 = 1 of cyanoacetylene (see Figs. 4b, d, and 5k, l), and there is a hint of emission toward P2 in the isotopologue HC13CCN while P1 is easily detected (see Figs. 4c and a). In addition, the wings of the main component of cyanoacetylene v7 = 1 are spatially shifted: the redshifted wing peaks about $1\hbox{$^{\prime\prime}$ }$ North-West of P1 while the blueshifted wing peaks about $1\hbox{$^{\prime\prime}$ }$ East of P1 (Figs. 5k and m). This East-West velocity gradient was previously reported by several authors (e.g. de Vicente et al. 2000; Hollis et al. 2003; Lis et al. 1993). Although it could result from cloud rotation, it is most likely a sign of outflow activity (see, e.g., Liu & Snyder 1999). The transition with highest energy in our PdBI sample is a transition of cyanoacetylene in the vibrationally excited state v4 = 1 ( $E_{\rm u}/k_{\rm B} = 1283$ K). Within the limits of our sensitivity, we detect emission only toward P1 in this highly excited transition (Fig. 5j). Finally, methylformate peaks at a position significantly offset from P1, at $1.7\hbox{$^{\prime\prime}$ }$ to the North-West (Fig. 5n). It has no counterpart in the continuum map of Fig. 5o. To sum up, our PdBI data reveal three main positions of molecular line emission (P1 and P2 corresponding to the methanol cores ``i'' and ``h'', and P3 the peak position of methylformate), and an East-West velocity gradient around P1.

Within the limits of our sensitivity, the amino acetonitrile features F2 to F6 detected with the PdBI show only one peak, and they all peak at the same position (Figs. 5a to e). We are confident that the emission detected in features F2 to F6 is not contaminated by the continuum since no significant signal is detected in the reference map (Fig. 5f). Their weighted-mean peak position was labeled P1 above (offset -1.5 $\pm$ $0.2\hbox{$^{\prime\prime}$ }$, 0.2 $\pm$ $0.2\hbox{$^{\prime\prime}$ }$, see Table 6). The fact that all features are detected at the same position is consistent with their assignment to the same molecule (see above the shifted position of methylformate for instance). The deconvolved major and minor axes of the emission detected in features F2 to F6 are in the range 0-2.2 $\hbox{$^{\prime\prime}$ }$ and 1.0-1.9 $\hbox{$^{\prime\prime}$ }$, respectively. The amino acetonitrile emission is therefore slightly resolved and has a size of roughly 2 $\hbox{$^{\prime\prime}$ }$ FWHM, which we used for the LTE modeling. The spatially integrated fluxes of F4 and F6 agree within 20$\%$ with the fluxes measured with the 30 m telescope (see Cols. 12 and 13 of Table 5). The emission detected with the 30 m telescope in these two features of amino acetonitrile is therefore compact (2 $\hbox{$^{\prime\prime}$ }$) and was not filtered out by the interferometer. The other features F2, F3, and F5 have 30 m fluxes 1.6, 1.4, and 3.8 times larger than the PdBI fluxes, respectively: the emission filtered out by the interferometer most likely corresponds to the unidentified transitions blended with these amino acetonitrile features (see Fig. 4a). In addition, the low signal-to-noise ratio of feature F5 detected with the PdBI may significantly affect the flux measurement.

We used the parameters of the 30 m model (see Table 4) to compute a model spectrum of amino acetonitrile with the spatial resolution of the PdBI (using the geometrical mean of the elliptical beam). The agreement with the peak spectrum is good, within a factor of 2 (see Figs. 4a and b). The small discrepancy may come from the somewhat uncertain source size and from our approximate modeling of the interferometric beam pattern: spherical beam and full uv coverage for the model versus elliptical beam and partially sampled uv coverage for the observations. Overall, our LTE model of amino acetonitrile is therefore well consistent with the compact emission detected with the PdBI.

   
3.5 Mapping amino acetonitrile with the ATCA


 

 
Table 6: Peak positions of continuum and molecular line emission detected with the PdBI and the ATCA toward Sgr B2(N).
  RA (J2000) Dec (J2000) Comments
  $17^{{\rm h}}47^{{\rm m}}$ $-28^\circ22\hbox{$^\prime$ }$  
  PdBI  
82 $19\hbox{$.\!\!^{\rm s}$ }886 \pm 0\hbox{$.\!\!^{\rm s}$ }005$ $18.4\hbox{$^{\prime\prime}$ }\pm 0.1\hbox{$^{\prime\prime}$ }$ continuum 82.0 GHz
P1 $19\hbox{$.\!\!^{\rm s}$ }89 \pm 0\hbox{$.\!\!^{\rm s}$ }01$ $18.8\hbox{$^{\prime\prime}$ }\pm 0.2\hbox{$^{\prime\prime}$ }$ mean AANa F2 to F6
P2 $19\hbox{$.\!\!^{\rm s}$ }88 \pm 0\hbox{$.\!\!^{\rm s}$ }01$ $13.5\hbox{$^{\prime\prime}$ }\pm 0.2\hbox{$^{\prime\prime}$ }$ mean HC3N v7=1, C2H5CN
P3 $19\hbox{$.\!\!^{\rm s}$ }79 \pm 0\hbox{$.\!\!^{\rm s}$ }01$ $17.8\hbox{$^{\prime\prime}$ }\pm 0.3\hbox{$^{\prime\prime}$ }$ peak CH3OCHO
  ATCA  
95 $19\hbox{$.\!\!^{\rm s}$ }87 \pm 0\hbox{$.\!\!^{\rm s}$ }01$ $18.7\hbox{$^{\prime\prime}$ }\pm 0.1\hbox{$^{\prime\prime}$ }$ mean continuum
      93.2 and 97.4 GHz
P4 $19\hbox{$.\!\!^{\rm s}$ }85 \pm 0\hbox{$.\!\!^{\rm s}$ }02$ $18.9\hbox{$^{\prime\prime}$ }\pm 0.2\hbox{$^{\prime\prime}$ }$ mean AAN F7 to F10
P5 $19\hbox{$.\!\!^{\rm s}$ }86 \pm 0\hbox{$.\!\!^{\rm s}$ }01$ $13.8\hbox{$^{\prime\prime}$ }\pm 0.1\hbox{$^{\prime\prime}$ }$ mean HC13CCN v7=1,
      CH3OH $v_{{\rm t}}=1$

a AAN stands for amino acetonitrile.



  \begin{figure}
\par\includegraphics[width=9cm,clip]{9203f6.eps}\end{figure} Figure 6: Spectra obtained with the Australia Telescope Compact Array (a) to j)) and the 30 m telescope (k) and l)) toward Sgr B2(N) (black histogram). The dotted lines show the frequency ranges listed in Table 7. The offset position with respect to the reference position of Fig. 7 is given in each panel. The lines identified in our 30 m survey are labeled in blue. The red spectrum shows our best-fit model for amino acetonitrile (AAN) while the green spectrum corresponds to the 30 m model including all molecules. The observed lines which have no counterpart in the green spectrum are still unidentified. a) and b) show the extended configuration H 214, c) and d) the intermediate configuration H 168, e) and f) the compact configuration H 75, g) and h) the combination of H 214 and H 168, and i) and j) the combination of all three configurations. The spectral coverage is not the same for all configurations because the sky tuning frequency for H 168 and H 75 was not corrected for the observatory velocity variations. The clean beam size ( HPBW) is given in each panel.

The two 3 mm spectral windows of the ATCA were chosen to cover the four amino acetonitrile features F7 to F10. The spectra toward position P4 of Sgr B2(N) (offset  $-2\hbox{$^{\prime\prime}$ }$, 0.1 $\hbox{$^{\prime\prime}$ }$) are presented for both windows in Fig. 6. Since the spectral windows were not exactly the same in each configuration (see Sect. 2.3), we show the spectra for each configuration (Figs. 6a to f), plus the combination of the two broadest ones (Figs. 6g and h), and the combination of all three configurations (Figs. 6i and j). Nearly all the lines seen with the 30 m telescope are detected with the ATCA toward P4. In the 90.6 GHz band, we detect the blue wing of an SO2 transition (Fig. 6a), the red wing of an HC13CCN ground-state transition (Fig. 6e), an unidentified line, and feature F7. In the 90.8 GHz band, we detect the low-velocity component of a $v_{{\rm t}}$ = 1 transition of methanol, the low-velocity component of a v7 = 1 transition of HC13CCN (Figs. 6d and f), and the three amino acetonitrile features F8, F9, and F10. Toward the northern position P5, we detect a second velocity component of methanol $v_{{\rm t}}=1$ and HC13CCN v7=1 (not shown in Fig. 6, see below).

The integrated intensity maps of the amino acetonitrile features F7 to F10 in the different configurations are presented in Figs. 7a to p, along with maps of the excited states of methanol and HC13CCN (Figs. 7q to v). The frequency intervals used to compute the integrated intensities are given in Cols. 3 and 4 of Table 7 and drawn in dotted lines in Fig. 6. We used the fitting routine GAUSS_2D of the GILDAS software to measure the position, size, and peak flux of each integrated emission. The results are listed in Cols. 6 to 11 of Table 7. We label P4 the weighted-mean peak position of features F7 to F10, computed using the combined configuration H 214 + H 168 (only H 214 for F8), and P5 the average northern peak position of methanol and HC13CCN. The mean peak position P4 is at the offset (-2.0 $\pm$ $0.3\hbox{$^{\prime\prime}$ }$, 0.1 $\pm$ $0.2\hbox{$^{\prime\prime}$ }$), and the average position P5 is at (-1.9 $\pm$ $0.1\hbox{$^{\prime\prime}$ }$, 5.2 $\pm$ $0.1\hbox{$^{\prime\prime}$ }$) (see coordinates in Table 6 and positions in Fig. 7x). Finally, the ATCA velocity-integrated flux spatially integrated over the emitting region is listed in Col. 12 of Table 7 and the 30 m velocity-integrated intensity is given in Col. 13.


 

 
Table 7: Measurements obtained toward Sgr B2(N) with the Australia Telescope Compact Array at 91 GHz.
Moleculea Conf.b $f_{{\rm min}}$c $f_{{\rm max}}$c $\sigma^d$ $F_{{\rm peak}}$e $\Delta\alpha$e $\Delta\delta$e $\theta_{{\rm maj}}^{{fwhm}}$ e $\theta_{{\rm min}}^{{fwhm}}$ e PAe $\Phi_{{\rm ATCA}}^f$ $\Phi_{{\rm 30~m}}^g$
    (MHz)) (MHz) (Jy/beam km s-1) ('') ('') ('') ('') ($^\circ $) (Jy km s-1) (Jy km s-1)
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13)
AAN F7 E 90 558.99 90 563.99 0.12 0.87 -2.32 $\pm$ 0.20 -0.22 $\pm$ 0.13 2.9 $\pm$ 0.4 2.2 $\pm$ 0.3 29.2 $\pm$ 0.1 1.12 3.06
AAN F7 I 90 559.05 90 564.05 0.15 1.47 -1.94 $\pm$ 0.20 0.58 $\pm$ 0.10 3.6 $\pm$ 0.4 2.7 $\pm$ 0.2 -79.8 $\pm$ 1.5 1.73 3.06
AAN F7 C 90 561.48 90 564.23 0.10 1.53 -0.96 $\pm$ 0.21 0.71 $\pm$ 0.17 7.0 $\pm$ 0.4 4.8 $\pm$ 0.3 -80.3 $\pm$ 0.0 1.37 1.79
AAN F7 M 90 559.13 90 563.96 0.12 1.19 -2.10 $\pm$ 0.16 0.25 $\pm$ 0.10 3.1 $\pm$ 0.3 2.7 $\pm$ 0.2 83.5 $\pm$ 0.0 1.71 2.96
AAN F7 A 90 562.03 90 563.96 0.06 0.61 -1.23 $\pm$ 0.15 0.26 $\pm$ 0.10 5.3 $\pm$ 0.3 3.3 $\pm$ 0.2 87.1 $\pm$ 22.5 1.37 1.00
AAN F8 E 90 781.27 90 786.77 0.21 1.22 -1.94 $\pm$ 0.24 -0.18 $\pm$ 0.16 3.8 $\pm$ 0.5 2.1 $\pm$ 0.3 45.0 $\pm$ 0.0 1.70 7.23
AAN F9 E 90 788.02 90 792.02 0.09 0.45 -1.70 $\pm$ 0.29 -0.06 $\pm$ 0.19 3.4 $\pm$ 0.6 1.9 $\pm$ 0.4 45.0 $\pm$ 0.1 0.49 2.14
AAN F9 I 90 788.11 90 792.11 0.13 0.97 -1.77 $\pm$ 0.26 0.23 $\pm$ 0.13 3.6 $\pm$ 0.5 2.2 $\pm$ 0.3 -84.0 $\pm$ 0.0 1.01 2.14
AAN F9 C 90 790.54 90 792.04 0.10 2.00 -1.25 $\pm$ 0.16 0.49 $\pm$ 0.13 6.1 $\pm$ 0.3 5.8 $\pm$ 0.3 -45.0 $\pm$ 0.0 1.86 1.59
AAN F9 M 90 788.04 90 792.16 0.10 0.85 -1.67 $\pm$ 0.17 0.02 $\pm$ 0.11 3.1 $\pm$ 0.3 2.4 $\pm$ 0.2 75.9 $\pm$ 0.1 1.07 2.14
AAN F9 A 90 790.95 90 792.16 0.05 0.63 -1.26 $\pm$ 0.14 0.23 $\pm$ 0.09 4.8 $\pm$ 0.3 3.9 $\pm$ 0.2 84.5 $\pm$ 0.0 1.51 1.31
AAN F10 E 90 796.52 90 800.77 0.16 1.17 -2.51 $\pm$ 0.20 0.02 $\pm$ 0.13 2.7 $\pm$ 0.4 2.2 $\pm$ 0.3 -81.2 $\pm$ 0.2 1.38 6.48
AAN F10 I 90 796.61 90 800.86 0.10 0.93 -1.81 $\pm$ 0.21 0.20 $\pm$ 0.11 3.3 $\pm$ 0.4 2.0 $\pm$ 0.2 82.3 $\pm$ 0.0 0.79 6.19
AAN F10 C 90 796.54 90 800.79 0.15 3.36 -1.08 $\pm$ 0.15 0.28 $\pm$ 0.12 6.6 $\pm$ 0.3 4.9 $\pm$ 0.2 -77.7 $\pm$ 0.0 2.78 6.48
AAN F10 M 90 796.52 90 800.88 0.13 1.32 -2.28 $\pm$ 0.15 0.03 $\pm$ 0.09 2.9 $\pm$ 0.3 2.2 $\pm$ 0.2 83.7 $\pm$ 22.5 1.42 6.48
AAN F10 A 90 796.52 90 800.88 0.13 1.82 -1.66 $\pm$ 0.12 0.12 $\pm$ 0.08 4.5 $\pm$ 0.2 3.1 $\pm$ 0.2 -89.3 $\pm$ 22.5 3.24 6.48
HC13CCN v7=1 HV I 90 804.36 90 805.36 0.05 0.49 -1.94 $\pm$ 0.20 5.16 $\pm$ 0.10 3.0 $\pm$ 0.4 2.0 $\pm$ 0.2 84.4 $\pm$ 0.0 0.41 2.39
HC13CCN v7=1 LV I 90 806.11 90 809.36 0.14 2.74 -1.56 $\pm$ 0.10 0.55 $\pm$ 0.05 3.7 $\pm$ 0.2 2.1 $\pm$ 0.1 83.6 $\pm$ 0.0 2.69 10.30
HC13CCN v7=1 LV C 90 806.04 90 809.29 0.15 4.98 -1.71 $\pm$ 0.10 0.25 $\pm$ 0.08 7.1 $\pm$ 0.2 4.4 $\pm$ 0.2 -83.8 $\pm$ 0.0 4.12 10.30
CH3OH $v_{{\rm t}}=1$ HV I 90 809.61 90 811.11 0.09 1.52 -1.85 $\pm$ 0.12 5.23 $\pm$ 0.06 3.7 $\pm$ 0.2 2.1 $\pm$ 0.1 -85.7 $\pm$ 0.1 1.54 6.55
CH3OH $v_{{\rm t}}=1$ LV I 90 812.36 90 814.11 0.11 1.60 -1.84 $\pm$ 0.13 0.44 $\pm$ 0.06 3.8 $\pm$ 0.3 3.6 $\pm$ 0.1 23.7 $\pm$ 22.5 2.72 10.40
CH3OH $v_{{\rm t}}=1$ LV C 90 812.29 90 814.29 0.12 5.22 -1.86 $\pm$ 0.08 -0.03 $\pm$ 0.06 7.1 $\pm$ 0.2 4.5 $\pm$ 0.1 -77.9 $\pm$ 0.0 4.29 10.40
a For amino acetonitrile (AAN), we give the feature number like in Col. 8 of Table 3. For the other molecules, HV and LV mean high and low velocity component, respectively.
b Interferometer configuration: E: extended (H 214), I: intermediate (H 168), C: compact (H 75), M: mixed (H 214 + H 168), A: all (H 214 + H 168 + H 75).
c Frequency range over which the intensity was integrated.
d Noise level in the integrated intensity map shown in Fig. 7.
e Peak flux, offsets in right ascension and declination with respect to the reference position of Fig. 7, major and minor diameters (FWHM), and position angle (East from North) derived by fitting an elliptical 2D Gaussian to the integrated intensity map shown in Fig. 7. The uncertainty in Col. 11 is the formal uncertainty given by the fitting routine GAUSS_2D, while the uncertainties correspond to the beam size divided by two times the signal-to-noise ratio in Cols. 7 and 8 and by the signal-to-noise ratio in Cols. 9 and 10.
f Flux spatially integrated over the region showing emission in the integrated intensity map of Fig. 7.
g Integrated flux of the 30 m spectrum computed over the frequency range given in Cols. 3 and 4.



  \begin{figure}
\par\includegraphics[angle=270,width=18cm,clip]{9203f7.eps}\end{figure} Figure 7: Integrated intensity maps (panels a) to v)) and continuum map (panel w)) obtained toward Sgr B2(N) with the Australia Telescope Compact Array at 3 mm. Panels a) to p) show the amino acetonitrile features F7 to F10 in the different configurations (see Fig. 6). Panels q) to v) show the other molecules listed in Table 7. The lower contour (positive in black solid line and negative in blue dotted line) and the contour step are 3$\sigma $ for panels a), b), d) to h), j) to m), and o) to q), 4$\sigma $ for panels r), t), and u), 5$\sigma $ for panels c), i) and n), and 6$\sigma $ for panels s) and v) (with $\sigma $ given in Col. 5 of Table 7). For panel w), the first contours are 3 and 6$\sigma $, and the contour step is 6$\sigma $ for the other contours (with $\sigma = 37$ mJy/beam). In each panel, the 0, 0 position is $\alpha_{{\rm J2000}} = 17^{{\rm h}}47^{{\rm m}}20\hbox{$.\!\!^{\rm s}$ }00$, $\delta _{{\rm J2000}} = -28^\circ 22\hbox {$^\prime $ }19.0\hbox {$^{\prime \prime }$ }$, the two thick plus symbols mark positions P4 and P5 (labeled in panel a)), and the filled ellipse in the top right corner shows the clean beam. The cross symbols in panel w) are the peak positions of the (ultracompact) H II regions detected by Gaume et al. (1995) at 1.3 cm (K9.69, and K1 to K6, from right to left). The spectral integration was done on the frequency ranges given in Table 7. The maps are not corrected for primary beam attenuation. Panel x) displays the ATCA positions P4 and P5 with thick plus symbols and the PdBI positions P1 to P3 with thin plus symbols, for visual comparison.

Since the line-free frequency ranges in the two spectral windows are too small to compute a reliable continuum map, we present in Fig. 7w a map combining the emission obtained at 93.2 and 97.4 GHz in the continuum mode. The contaminating lines were avoided in the integration. The continuum emission detected with the ATCA has properties very similar to the emission detected with the PdBI (see Sect. 3.4). The emission peaks at $\alpha_{{\rm J2000}} = 17^{{\rm h}}47^{{\rm m}}19\hbox{$.\!\!^{\rm s}$ }87$ $\pm$ $0\hbox{$.\!\!^{\rm s}$ }01$, $\delta_{{\rm J2000}} = -28^\circ22\hbox{$^\prime$ }18.7\hbox{$^{\prime\prime}$ }$ $\pm$ $0.1\hbox{$^{\prime\prime}$ }$, i.e. within 0.3 $\hbox{$^{\prime\prime}$ }$ of the ultracompact H II region K2 (Gaume et al. 1995). The continuum emission is somewhat extended around the main peak: it extends toward the other ultracompact H II regions K1, K3, and the shell-like H II region K5, but these features are not resolved with the ATCA. We also detect a shell-like emission close to K6, but its signal-to-noise ratio is lower than in the PdBI data. We do not detect any emission toward the weak ultracompact H II region K9.69 (Gaume et al. 1995).

The strong methanol $v_{{\rm t}}=1$ and HC13CCN v7=1 lines show the same structure as the strong lines detected with the PdBI, namely emission from two different positions separated by about 5.1 $\hbox{$^{\prime\prime}$ }$ in declination, each with a distinct velocity (Figs. 7q, r, t, and u). These two positions P4 and P5 coincide with the PdBI positions P1 and P2, respectively, within 0.5 $\hbox{$^{\prime\prime}$ }$ which is about one fifth of the ATCA synthesized beam (see Fig. 7x for a visual comparison). Therefore we are very confident that they correspond to the same regions. The third position P3 detected with the PdBI in methylformate is not detected in the small number of transitions observed with the ATCA.

Within the limits of our sensitivity, the amino acetonitrile features F7 to F10 show only one peak, and they all peak at the same position P4 coincident with the PdBI position P1. Therefore, all amino acetonitrile features detected with both the ATCA and the PdBI peak at the same position, which is consistent with their assignment to the same molecule. The emission detected in features F7 to F10 is barely resolved with the ATCA. Given the uncertainties, it is consistent with the source size of 2 $\hbox{$^{\prime\prime}$ }$ suggested by our measurements with the PdBI. The ATCA spatially integrated flux of feature F7 in the mixed configuration H 214 + H168 agrees with the 30 m telescope flux within 40$\%$. Given the calibration uncertainties of both instruments, and the somewhat larger noise in the 30 m spectrum, most of the flux of feature F7 is recovered with the ATCA. On the other hand, the ATCA spatially integrated fluxes of features F8 to F10 are significantly weaker than the 30 m telescope fluxes. The main reason for this disagreement may be the contamination of the 30 m spectrum by emission from transitions of other molecules which are still unidentified in our survey (see Fig. 6l). This contaminating emission is missed by the interferometer either because it peaks at an offset position or because it is extended and filtered out.

The model spectrum of amino acetonitrile computed with the same parameters as the 30 m model (see Table 4) but with the spatial resolution of the ATCA is shown in red in Figs. 6a to j. The agreement with the spectra obtained with the ATCA is good, within a factor of 2 (see comment about the interferometric modeling in Sect. 3.4). Overall, our LTE model of amino acetonitrile is therefore well consistent with the compact emission detected with the ATCA.

   
3.6 Abundance of amino acetonitrile in Sgr B2(N)

The continuum emission detected with the PdBI (see Fig. 5o) has a peak intensity of 0.459 $\pm$ 0.009 Jy/ $3.3\hbox{$^{\prime\prime}$ }$ $\times $ $0.8\hbox{$^{\prime\prime}$ }$-beam. In the 2''-diameter region convolved with the PdBI beam centered on the AAN peak position P1 (convolved FWHM: $3.9\hbox{$^{\prime\prime}$ }$ $\times $ $2.2\hbox{$^{\prime\prime}$ }$), we measure a mean intensity of 0.257 Jy/beam and a flux of 0.556 Jy. The continuum emission from Sgr B2(N) at 3.7 mm is dominated by thermal dust emission, at most 30$\%$ come from free-free emission (Kuan et al. 1996), probably even less toward the ultracompact H II region K2 since its flux is only 20 and 60 mJy at 2 and 1.3 cm, respectively (Gaume & Claussen 1990; Gaume et al. 1995). In addition, the thermal dust emission is optically thin (Carlstrom & Vogel 1989), so we can estimate the H2 column density using the equation:

\begin{displaymath}%
N_{{\rm H}_2} = \frac{S_\nu^{{\rm beam}}}{\Omega_{{\rm beam}} \mu m_{{\rm H}} \kappa_\nu B_\nu(T_{{\rm dust}})},
\end{displaymath} (1)

with $S_\nu^{{\rm beam}}$ the intensity at $\nu = 82.0$ GHz, $\Omega_{{\rm beam}} = 7.19$ $\times $ 10-11 rad2 the solid angle of the synthesized beam, $\mu = 2.33$ the mean molecular weight, $m_{{\rm H}}$ the mass of atomic hydrogen, $\kappa_\nu$ the dust mass opacity (for a standard gas-to-dust ratio of 100 by mass), and $B_\nu(T_{{\rm dust}})$ the Planck function at the dust temperature  $T_{{\rm dust}}$. We assume a dust mass opacity $\kappa_\nu$(230 GHz) = 0.01 cm2 g-1 valid for dust grains that have coagulated at high density and acquired ice mantles (Ossenkopf & Henning 1994) and a dust emissivity exponent $\beta = 1.5$, which yield a dust mass opacity  $\kappa_\nu$(82 GHz) = 0.0036 cm2 g-1. Since gas and dust are thermally well coupled via collisions at densities above $\sim$105 cm-3 (see, e.g., Lesaffre et al. 2005), we assume a dust temperature equal to the excitation temperature derived for amino acetonitrile (100 K, see Table 4 and Fig. 2). We obtain a mean H2 column density $N_{{\rm H}_2} = 1.3$ $\times $ 1025 cm-2 in the inner region where we detect the amino acetonitrile emission with the PdBI. Assuming a distance of 8 kpc (see Sect. 1.1), the central region of deconvolved FWHM diameter 2 $\hbox{$^{\prime\prime}$ }$ has a linear diameter of 16 000 AU. We derive a total mass of 2340 $M_\odot$ from its integrated flux (0.556 Jy). Assuming spherical symmetry, this translates into a mean density $n_{{\rm H}_2} = 1.7$ $\times $ 108 cm-3.

Using the column density derived from our modeling (see Table 4), we find an amino acetonitrile abundance relative to H2 of about 2.2 $\times $ 10-9 in the inner region of deconvolved FWHM diameter 2 $\hbox{$^{\prime\prime}$ }$, with an uncertainty on the abundance of at least a factor of 2 given the uncertainties on the dust mass opacity and the dust emissivity exponent.

The continuum emission detected with the ATCA at a mean frequency of 95.3 GHz has a peak intensity of 1.00 Jy/ $3.5\hbox{$^{\prime\prime}$ }$ $\times $ $2.4\hbox{$^{\prime\prime}$ }$-beam. This intensity is 1.8 times larger than the PdBI continuum flux measured over an area $3.9\hbox{$^{\prime\prime}$ }$ $\times $ $2.2\hbox{$^{\prime\prime}$ }$ (see above). If this flux difference comes from the frequency dependence of the continuum emission, then we derive a frequency exponent of 3.9 which is, within the calibration uncertainties, consistent with the exponent of 3.5 expected for thermal dust emission with a dust emissivity exponent $\beta = 1.5$ assumed above. We are therefore confident that the continuum emission detected toward K2 with the PdBI and the ATCA is largely dominated by thermal dust emission.

   
3.7 Limits on possible extended emission of cold amino acetronitrile with the VLA


  \begin{figure}
\par\includegraphics[width=8.6cm,clip]{9203f8.eps}\end{figure} Figure 8: Continuum image of the Sgr B2 region obtained with the Very Large Array at 9.1 GHz . The lowest contour level is 4 times the rms noise level of 8 mJy beam-1 and contours double in value until they reach 512 times that level. The dotted circle represents the FWHM of the VLA antennas' primary beam at 9.1 GHz. The image is not corrected for attenuation due to the primary beam's response. Note that it is produced from data taken over only a 1 h period and has limited dynamic range and sensitivity. It is, however, consistent with the higher sensitivity three-pointing-mosaic 4.8 GHz image presented by Mehringer et al. (1995), which has a similar resolution. The synthesized beam is represented in the lower left corner. The upper and lower shaded circles are centered at the Sgr B2(N) and (M) pointing positions of our 30 m telescope spectral line survey, respectively. Their size corresponds to the $25\hbox {$^{\prime \prime }$ }$ FWHM of the 30 m telescope at 100 GHz.

Figure 8 shows the continuum image of the Sgr B2 region we obtained at 9.1 GHz with the VLA. At this frequency, the primary beam has a FWHM of $\sim$ $5\hbox{$^\prime$ }$. Our uv-data should adequately sample structures with sizes of up to $1.5\hbox{$^\prime$ }$. There are two major continuum sources, Sgr B2(N) and (M), whose emission is a blend of the contributions of many separate sources that are resolved in higher resolution images (e.g., Gaume et al. 1995). A number of secondary sources are evident. The peak brightness, $S_{\rm p}$, toward Sgr B2(N) is 2.85 Jy beam-1. Toward Sgr B2(M) we measure $S_{\rm p} = 4.12$ Jy beam-1. The image has a relatively high 1$\sigma $ rms noise level of 8.4 mJy beam-1 that is determined by dynamic range limitations. Nowhere in the whole line datacube do we find any significant line emission or absorption above 3.4 mJy beam-1 (5 times the 1$\sigma $ rms noise level in the images of the spectral line emission). This corresponds to a brightness temperature upper limit of 0.35 K. With this, and assuming a width of 30 km s-1, similar to other lines with extended emission (e.g., Hollis et al. 2004; Hunt et al. 1999) we can use the standard relation to calculate an upper limit to the column densities of the upper levels of the strongest of the JKa,Kc = 101-000 hfs components of $\sim$$\times $ 1012 cm-2. Hollis et al. (2004) use a two temperature component picture to explain their multitransition glycolaldehyde study, invoking components with temperatures of T = 8 and 50 K. For 8 K, our limit on the total column density of extended amino acetonitrile would be $\sim$$\times $ 1014 cm-2 and for 50 K it would be $\sim$$\times $ 1016 cm-2. The low-T value is on the same order as the total column density of glycolaldehyde that Hollis et al. (2004) calculate for this temperature.

Using the ATCA, Hunt et al. (1999) imaged Sgr B2 in the J=1-0 line of HC3N at a frequency near 9.1 GHz, very close to our amino acetonitrile frequency. In their $4.4\hbox{$^{\prime\prime}$ }$ $\times $ $9.9\hbox{$^{\prime\prime}$ }$ resolution images they found the spatial distribution of the line emission to resemble that of the continuum emission very closely. Assuming that possible extended amino acetonitrile had a similar distribution, the high continuum flux densities allow us to determine very sensitive limits on possible absorption (or weakly inverted emission) toward the continuum emission. We calculate very low $5\sigma$ limits on the absolute value of the optical depth of 8.3 $\times $ 10-4 and 1.2 $\times $ 10-3 toward Sgr B2(N) and (M). This implies $\sim$125 and 20 times lower column density limits for T = 8 and 50 K, respectively, compared to limits on possible thermal emission quoted above.

   
4 Discussion

   
4.1 Amino acetonitrile in Sgr B2(N)

We detected compact emission from amino acetonitrile in Sgr B2(N) with a source size of 2 $\hbox{$^{\prime\prime}$ }$ FWHM, a column density of 2.8 $\times $ 1016 cm-2, an excitation temperature of 100 K, a linewidth of 7 km s-1, and a centroid velocity of 64 km s-1 (see Table 4). We estimated the abundance of amino acetonitrile to be 2.2 $\times $ 10-9 in this compact region. We found no evidence for a possible colder, more extended emission. The compact emission peaks at position P1 (see Sect. 3.4 and Table 6), which is located 0.4 $\hbox{$^{\prime\prime}$ }$ South of the ultracompact H II region K2 where the 3.7 mm thermal dust continuum emission detected with the PdBI also peaks. This angular separation is at a level of 2$\sigma $ only, so it may not be significant. Our PdBI and ATCA data show that ethyl cyanide C2H5CN, cyanoacetylene HC3N in its excited states v7 = 1 and v4 = 1, HC13CCN in its excited state v7 = 1, and methanol CH3OH in its excited state $v_{{\rm t}}=1$ also peak at this position P1. The amino acetonitrile emission arises therefore from the hot core region called the ``Large Molecule Heimat'' (see Sect. 1.1.2). Our PdBI continuum data show that this compact region is extremely dense (1.7 $\times $ 108 cm-3) and massive (2340 $M_\odot$). The ultracompact H II region K2 is most likely still embedded in the dense, hot core traced by the thermal dust emission and seems therefore to be the youngest source among the numerous ultracompact H II regions populating the Sgr B2 molecular cloud. In addition, the LMH hosts the powerful Sgr B2(N) H2O maser region. The distribution of the maser emission over $4\hbox{$^{\prime\prime}$ }$ $\times $ $2\hbox{$^{\prime\prime}$ }$ was mapped using Very Long Baseline Interferometry by Reid et al. (1988), who also fitted a kinematical model invoking expansion and rotation. The best fit center of expansion is displaced from our interferometric position P1 by ( $\Delta \alpha, \Delta \delta$) = ( $-0.49\hbox{$^{\prime\prime}$ },-0.66\hbox{$^{\prime\prime}$ }$), which is less than the combined positional uncertainty of the VLBI and PdBI data. The best fit radial component of the expansion velocity, 63 $\pm$ 3 km s-1, is also in excellent agreement with the 64 km s-1 that we obtain for the LMH (see Table 4). H2O masers are associated with young stellar objects in their earliest stages when they drive powerful outflows, such as the one found in Sgr B2(N) which has a total velocity extent of $\sim$$\pm 50$ km s-1 (see, e.g., Reid et al. 1988). Thus, the water vapor maser provides evidence for the youth of the LMH, the very compact region where the amino acetonitrile emission originates from.

Bisschop et al. (2007) measured the abundances of various complex molecules in massive hot core regions and classified these molecules as ``cold'' (<100 K) or ``hot'' (>100 K). Based on the high abundances, the similar high rotation temperatures, and the relative constant abundance ratios of the oxygen-bearing species and two nitrogen-bearing species, they concluded that the ``hot'' molecules share a common solid state formation scheme. From an analysis of the emission of complex organic molecules in molecular clouds in the Galactic center region and a comparison to results previously obtained in hot cores, Requena-Torres et al. (2006) support also the scenario in which complex organic molecules are formed on the grain surfaces. The high temperature and abundance we measured for amino acetonitrile suggest it shares the same properties as the ``hot'' molecules found by Bisschop et al. (2007), which favors its formation on the grain surfaces, although its detection in other hot cores to check if it follows the abundance correlations found by Bisschop et al. (2007) and Requena-Torres et al. (2006) is needed to prove this conclusion.

Wirström et al. (2007) failed to detect amino acetonitrile in the hot cores Orion KL, W51 e1/e2, S140, and W3(OH) with the Onsala 20 m telescope. They found beam-averaged column density upper limits of 1.1-3.5 $\times $ 1013 cm-2 for amino acetonitrile, while they detected vinylcyanide C2H3CN with a column density of $\sim$$\times $ 1014 cm-2 in the first two sources. Our 30 m observations of Sgr B2(N) imply a column density of 8 $\times $ 1017 cm-2 for vinylcyanide with a source size of 2.3 $\hbox{$^{\prime\prime}$ }$ (Belloche et al., in prep.), i.e. about 30 times our amino acetonitrile column density. If the column density ratio of these two species in Sgr B2(N) holds for other hot cores, then the observations of Wirström et al. (2007) were not sensitive enough to detect amino acetonitrile in their sources.

Our PdBI and ATCA data show that the double peak structure seen in many transitions detected with the 30 m telescope are produced by two sources separated by about 5.3 $\hbox{$^{\prime\prime}$ }$ in the North-South direction (positions P1 and P2, see Sect. 3.4). The centroid velocity difference between these two positions is about 9 km s-1. The northern and more redshifted source (P2) is about twice weaker in the molecular emission detected in our 30 m data (Belloche et al., in prep.). These two sources were already detected in ethylcyanide with high-resolution observations (see, e.g., Jones et al. 2007; Liu & Snyder 1999; Hollis et al. 2003). Our interferometric data show that cyanoacetylene HC3N and its isotopologue HC13CCN in their excited state v7 = 1, and methanol in its excited state $v_{{\rm t}}=1$ are also detected toward both sources. In the PdBI spectra shown in Figs. 4c and d, we do not find a clear evidence for amino acetonitrile at a velocity of $\sim$73 km s-1. There may be a hint of emission at a level about a factor of 2 lower than the emission toward P1 (see also Feature F3 in the 30 m spectrum in Fig. 4g), but it is below our 3$\sigma $ detection limit. Therefore we cannot rule out that amino acetonitrile shares the same property as, e.g., ethylcyanide, cyanoacetylene, and methanol and is also present in the northern source P2 at a level about twice lower than in P1.

The molecular source P2 is not detected at a 3$\sigma $ level of 26 mJy/ $3.4\hbox{$^{\prime\prime}$ }$ $\times $ $0.81\hbox {$^{\prime \prime }$ }$-beam in the continuum map we obtained with the PdBI at 82.0 GHz (see Fig. 5o). On the other hand, we detect some emission with an intensity of 280 mJy/ $3.5\hbox{$^{\prime\prime}$ }$ $\times $ $2.4\hbox{$^{\prime\prime}$ }$-beam in the continuum map obtained with the ATCA at a mean frequency of 95.3 GHz (see Fig. 7w). If this emission is more extended than the PdBI beam, then the PdBI upper limit translates into 79 mJy in the ATCA beam, which yields an unphysical frequency exponent of $\sim$8 for the continuum emission toward P2 (see Sect. 3.6). We suspect that the ATCA continuum toward P2 is contaminated by a low-level line emission. In any case, since the continuum emission toward P2 is much weaker than toward P1 at 3 mm, P2 must be less dense and/or less hot than the hot core P1. P2 coincides with a weak blob of emission in the 1.3 cm VLA map of Gaume et al. (1995) (see their Figs. 6 and 7). However, this blob is located within the shell-like, weak, extended emission associated with K5 and it is difficult to know if it is compact or not from the 1.3 cm map published by these authors. Therefore the hot core P2 traced by the molecular emission may also be associated with an ultracompact H II region, weaker than K2. Alternatively, if it is not directely associated with a compact source of free-free emission, it may have been formed by the interaction of the shell-like structure K5 with the ambient medium, and could be in an earlier stage of evolution than the hot core P1 (LMH) associated with the ultracompact H II region K2.

   
4.2 Amino acetonitrile in Sgr B2(M)

We do not detect amino acetonitrile in our 30 m survey toward Sgr B2(M). Using the same parameters as for Sgr B2(N) (100 K and a FWHM source size of $2\hbox{$^{\prime\prime}$ }$), we find a $\sim$$3\sigma$ column density upper limit of 6 $\times $ 1015 cm-2 in the LTE approximation. The column density of amino acetonitrile is thus at least a factor $\sim$5 weaker toward Sgr B2(M) than toward Sgr B2(N). This is not surprising since, e.g., Nummelin et al. (2000) found that hot-core-type molecules are more abundant in Sgr B2(N) by factors 3-8 as compared to Sgr B2(M).

   
4.3 Amino acetonitrile, a precursor of glycine?

Amino acids, building blocks of proteins and therefore key ingredients to explain the origin of life, have been found in meteorites on Earth. Their deuterium isotopic composition suggests that they, or at least their direct precursors, were formed in the cold interstellar medium (e.g. Pizzarello & Huang 2005). Looking for amino acids in the interstellar medium is therefore appealing. However, the simplest amino acid glycine has been intensively searched for in the past 30 years, but has unfortunately not been discovered yet (e.g. Snyder et al. 2005; Brown et al. 1979; Cunningham et al. 2007).

Amino acetonitrile was proposed early on as a possible direct precursor of glycine in the interstellar medium (e.g. Brown et al. 1977). The formation of glycine via a Strecker-cyanohydrin synthesis has long been favored (Peltzer et al. 1984; Ehrenfreund et al. 2001; Bernstein et al. 2004). This pathway involves a carbonyl compound (such as an aldehyde or a ketone), hydrogen cyanide, and ammonia, and produces the amino nitrile which, after hydrolysis, yields the amino acid. However, the Strecker synthesis cannot explain the higher deuterium fractionation of amino acids compared to hydroxy acids which was measured in meteorites (see Elsila et al. 2007, and references therein).

Amino acids were successfully produced in the laboratory by UV-photolysis of ice mixtures mimicking the mantles of insterstellar grains (Bernstein et al. 2002; Muñoz Caro et al. 2002). For an ice mixture composed of H2O, CH3OH, NH3, and HCN, Woon (2002) proposed theoretically a pathway of radical-radical reactions involving the radicals t-HOCO and CH2NH2 produced by UV irradiation. This hypothesis was tested and verified experimentally by Holtom et al. (2005) with an ice mixture of CH3NH2 and CO2 bombarded by energetic electrons mimicking the impact of cosmic rays in the interstellar medium. This pathway leading to glycine does not involve the formation of amino acetonitrile. On the other hand, Elsila et al. (2007) experimented the UV-photolysis of an ice mixture of H2O, CH3OH, HCN, and NH3, and found with isotopic labeling techniques multiple pathways leading to the formation of amino acids. The main pathway involves the formation of the amino nitrile and they proposed ``a modified radical-radical mechanism that takes into account the formation of nitriles as amino acid precursor molecules''. They also noticed that a Strecker-type synthesis may be at most a minor contributor to the formation of glycine.

The formation of glycine in the gas phase was also investigated. Blagojevic et al. (2003) synthesized ionized glycine via the reaction of the hydroxylamine ion NH2OH+ with acetic acid CH3COOH. They proposed the formation of the precursor hydroxylamine NH2OH in the grain mantles and the formation of acetic acid via ion-molecule reactions in the gas phase. Based on quantum chemical calculations, Maeda & Ohno (2006) found another pathway to form glycine in the gas phase involving barrierless reactions between closed-shell species. Their pathway starts from CO2, NH3, and CH2, and leads to glycine via the reaction of CO2 with the closed-shell molecule CH2NH3, a higher energy isomer of methylamine CH3NH2. However, they mentioned that CH2NH3 should be efficiently destroyed by H2O, so this pathway may be unlikely in the interstellar gas phase where water can be very abundant. Both gas phase formation routes do not involve amino acetonitrile as a direct precursor of glycine.

This brief overview of the experimental and theoretical work on the formation of amino acids in the interstellar medium shows that there is no consensus about the chemical precursors of amino acids. It is however important to note that the amino acids produced in the ice experiments mentioned above (except Holtom et al. 2005) are found experimentally after the hydrolysis of the ice residues. It is possible that only their precursors (e.g. amino nitriles) are synthesized by the ice photochemistry, and that the amino acids are formed only later, e.g. on the comet/asteroids surfaces, by hydrolysis (Elsila et al. 2007). Therefore amino acetonitrile may well be a direct precursor of glycine.

The formation of amino acetonitrile itself was also investigated theoretically by Koch et al. (2008). They found that water can efficiently catalyze a reaction between methylenimine CH2NH and hydrogen isocyanide HNC to form amino acetonitrile in the grain mantles at a temperature of 50 K. Methylenimine was detected in the gas phase toward Sgr B2(N) by, e.g., Nummelin et al. (2000). They found evidence for both hot, compact and cold, extended components and derived a column density of 3.3 $\times $ 1017 cm-2 for the compact component, with a source size of 2.7 $\hbox{$^{\prime\prime}$ }$ and a temperature of 210+400-80 K, which is consistent with our own analysis (Belloche et al., in prep.). This column density is an order of magnitude larger than the column density we derived for amino acetonitrile, which does not rule out methylenimine as a precursor of amino acetonitrile.

   
4.4 Glycine in Sgr B2(N)

The frequency coverage of our 30 m survey of Sgr B2(N) includes many transitions of glycine as listed in the CDMS catalog (entries 75 511 and 75 512), but we do not detect this molecule within the limits of our LTE analysis. Using the same parameters as for amino acetonitrile (100 K and a source size of 2 $\hbox{$^{\prime\prime}$ }$, see Table 4), we derive a column density upper limit of 2.0 $\times $ 1017 cm-2 for conformer I and 5.0 $\times $ 1015 cm-2 for conformer II. Alternatively, the upper limit on emission from glycine more extended than the 30 m beam at 3 mm ($\sim$ $26\hbox{$^{\prime\prime}$ }$) is 1.2 $\times $ 1015 cm-2 for conformer I and 3.0 $\times $ 1013 cm-2 for conformer II. For a temperature of 75 K, we find column density upper limits for conformer I of 1.5 $\times $ 1017 cm-2 for a source size of 2 $\hbox{$^{\prime\prime}$ }$ and 8.9 $\times $ 1014 cm-2for emission more extended than the 30 m beam, and for conformer II 3.7 $\times $ 1015 cm-2 and 2.2 $\times $ 1013 cm-2, respectively.

Jones et al. (2007) did not detect glycine conformer I in Sgr B2(N) with the ATCA and derived a 3$\sigma $ upper limit of 1.4 $\times $ 1015 cm-2 for the beam-averaged column density at 75 K, which translates into an upper limit of 2.0 $\times $ 1016 cm-2 for a source size of 2 $\hbox{$^{\prime\prime}$ }$ after correction for beam dilution ( $17.0\hbox{$^{\prime\prime}$ }$ $\times $ $3.4\hbox{$^{\prime\prime}$ }$). This upper limit on any compact emission from glycine is at a level 8 times lower than the one we derive with the 30 m telescope. As Jones et al. (2007) mentioned, the tentative detection of Kuan et al. (2003) is inconsistent with this upper limit in the case of compact emission. On the other hand, the ATCA non-detection does not exclude extended emission at the level found by Kuan et al. (2003) who reported a beam-averaged column density of 4.2 $\times $ 1014 cm-2 with the NRAO 12 m telescope and a rotational temperature of 75 K. However Cunningham et al. (2007) did not detect glycine conformer I in Sgr B2(N) with the 22 m Mopra telescope and derived a 3$\sigma $ upper limit of 3.7 $\times $ 1014 cm-2 for the beam-averaged column density at 75 K. This upper limit is at a level 2.4 times lower than our beam-averaged upper limit. However, their upper limit was derived for a position offset by 26 $\hbox{$^{\prime\prime}$ }$ from the hot core position, so it only rules out emission from Sgr B2(N) more extended than $\sim$ $50\hbox{$^{\prime\prime}$ }$ in diameter. If glycine's emission were centered on the hot core position with a diameter of $\sim$ $25\hbox {$^{\prime \prime }$ }$, Mopra would have missed $\sim$$80\%$ of the flux, and their upper limit would be 1.9 $\times $ 1015 cm-2. In that case, our upper limit is more significant, but not low enough to rule out the tentative detection reported by Kuan et al. (2003) if glycine is confined to a source size of $\sim$ $30\hbox{$^{\prime\prime}$ }$. However, the arguments presented by Snyder et al. (2005) do rule out this case. As a conclusion, the upper limits of Cunningham et al. (2007), Jones et al. (2007), and Snyder et al. (2005) rule out emission of glycine conformer I at the level reported by Kuan et al. (2003) in Sgr B2(N) for any source size.

Cunningham et al. (2007) found an upper limit of 7.7 $\times $ 1012 cm-2for the beam-averaged column density of glycine conformer II with Mopra toward the central position of Sgr B2(N). This upper limit is nearly a factor of 3 lower than the upper limit we derived above with the 30 m telescope for extended emission. With the ATCA, Jones et al. (2007) found an upper limit of 8.6 $\times $ 1013 cm-2 for the beam-averaged column density, which translates into 1.2 $\times $ 1015 cm-2 for a source size of 2 $\hbox{$^{\prime\prime}$ }$. This upper limit is again a factor of 3 lower than the upper limit we derived above with the 30 m telescope for compact emission.

Bernstein et al. (2004) found experimentally that organic acids are less stable than organic nitriles against UV photodestruction but they concluded that in dense molecular clouds, the ratio nitrile to acid should be affected by less than a factor of 2 over the lifetime of the cloud. Therefore it could be instructive to compare the pairs methylcyanide/acetic acid (CH3CN/CH3COOH) and amino acetonitrile/glycine (NH2CH2CN/NH2CH2COOH). In our 30 m line survey (Belloche et al., in prep.), we derive a column density ratio on the order of 200 for CH3CN/CH3COOH toward Sgr B2(N). If the two pairs are produced by similar chemical pathways yielding similar column density ratios, then we expect the glycine column density to be two orders of magnitude smaller than the amino acetonitrile column density, i.e. about 2 $\times $ 1014 cm-2 for a compact source of 2 $\hbox{$^{\prime\prime}$ }$ diameter, which is nearly two orders of magnitude smaller than the upper limit derived above for glycine conformer I from the ATCA measurements of Jones et al. (2007), and a factor 5 smaller for conformer II. Therefore glycine emission may be well below the confusion limit in Sgr B2(N).

   
5 Conclusions

We used the complete 3 mm and partial 2 and 1.3 mm line surveys obtained with the IRAM 30 m telescope toward the hot cores Sgr B2(N) and (M) to search for emission from the complex molecule amino acetonitrile. We carried out follow-up observations with the IRAM Plateau de Bure and ATCA interferometers at selected frequencies. We also looked for extended emission from cold amino acetonitrile with the VLA. We report the detection of amino acetonitrile toward the hot core Sgr B2(N)-LMH, which is the first detection of this molecule in the interstellar medium. Our main results and conclusions are the following:

1.
In the course of this work, we prepared an amino acetonitrile entry (56 507) for the catalog of the Cologne Database for Molecular Spectroscopy (CDMS) using the laboratory transition frequencies reported by Bogey et al. (1990).

2.
88 of the 398 significant transitions of amino acetonitrile covered by our 30 m line survey are relatively free of contamination from other molecules and are detected in the form of 51 observed features toward Sgr B2(N).

3.
Nine features out of 51 were followed-up upon and detected with the IRAM PdB and ATCA interferometers. The amino acetonitrile emission looks compact and we derive a source size of about 2 $\hbox{$^{\prime\prime}$ }$ in diameter (FWHM).

4.
With a source size of 2 $\hbox{$^{\prime\prime}$ }$ and an LTE analysis, we derive an amino acetonitrile column density of 2.8 $\times $ 1016 cm-2 for a temperature of 100 K and a linewidth of 7 km s-1.

5.
The compact continuum emission detected with the PdB interferometer yields a mean H2 column density $N_{{\rm H}_2} = 1.3$ $\times $ 1025 cm-2 in the central region of diameter 2 $\hbox{$^{\prime\prime}$ }$ for a temperature of 100 K, which implies a mean density $n_{{\rm H}_2} = 1.7$ $\times $ 108 cm-3, a mass of 2340 $M_\odot$, and an amino acetonitrile fractional abundance of 2.2 $\times $ 10-9.

6.
The high abundance and temperature may indicate that amino acetonitrile is formed by grain surface chemistry.

7.
We detected emission from ethylcyanide C2H5CN, cyanoacetylene HC3N and its isotopologue HC13CCN in their v7=1 excited states, and methanol CH3OH in its excited state $v_{{\rm t}}=1$ in two compact sources toward Sgr B2(N). The two sources are separated by about $5.3\hbox{$^{\prime\prime}$ }$ in the North-South direction and by 9 km s-1 in velocity. They produce double peaked line shapes for many molecules detected in our 30 m line survey. Only the southern source is detected with the PdBI in continuum emission. It is associated with the ultracompact H II region K2 and a powerful H2O maser region, and must be very young. The northern source is weaker in molecular emission and must be less dense and/or less hot. It may be associated with a weaker ultracompact H II region and may be in an even earlier stage of evolution. The sensitivity of our observations was not good enough to detect amino acetonitrile toward the northern source. It is at least a factor of 2 weaker than toward the southern source.

8.
We did not detect amino acetonitrile toward Sgr B2(M) and derived a column density upper limit of 6 $\times $ 1015 cm-2.

9.
We failed to detect any extended emission from cold amino acetonitrile with the VLA and derived a column density upper limit of 3 $\times $ 1012-14 cm-2 at 8 K.

10.
Amino acetonitrile may be a chemical precursor of glycine. We did not detect the glycine conformers I and II in our 30 m line survey. The column density upper limits we derive are less constraining than upper limits previously published by other authors. Based on our detection of amino acetonitrile and a comparison to the pair methylcyanide/acetic acid (CH3CN/CH3COOH) both of which are detected in our survey, we conclude that the column density of glycine conformers I and II in Sgr B2(N) may be two orders of magnitude and a factor 5 below the current best upper limits, respectively, which would be below the confusion limit of Sgr B2(N) in the 1-3 mm range.

Acknowledgements
We thank the IRAM staff in Grenoble for observing at the PdBI and for their help with the data reduction, the IRAM staff in Granada for service observing in January 2005, and Sergio Martin for providing the reference (off) position for our 30 m observations. We thank John Pearson for his predictions of the first excited state of ethylcyanide, Claus Nielsen for providing transition frequencies of formamide isotopologues, Isabelle Kleiner, Vadim Ilyushin, and Frank Lovas for acetic acid frequencies, and Brian Drouin for his predictions of acetone. H.S.P.M. and the CDMS had been supported initially through the Deutsche Forschungsgemeinschaft (DFG) via the collaborative research grant SFB 494. Recent support is provided by the Bundesministerium für Bildung und Forschung administered through Deutsches Zentrum für Luft- und Raumfahrt (DLR; the German space agency). J.O. is a Jansky Fellow of the National Radio Astronomy Observatory. C.H. is a fellow of the Studienstiftung des deutschen Volkes and member of the International Max-Planck Research School for Radio and Infrared Astronomy.

References

 

  
6 Online Material


   
Table 2: Transitions of amino acetonitrile observed with the IRAM 30 m telescope toward Sgr B2(N). The horizontal lines mark discontinuities in the observed frequency coverage. All lines with $S\mu ^2$ < 20 D2 are not listed, since they are expected to be much too weak to be detectable with our sensitivity.
Na Transitionb Frequency Unc.c $E_{\rm l}$d $S\mu ^2$ $\sigma^e$ Comments
    (MHz) (kHz) (K) (D2) (mK)  
(1) (2) (3) (4) (5) (6) (7) (8)
1 9 0, 9-8 0, 8 80 947.479 7 16 60 33 Detected
2 9 2, 8-8 2, 7 81 535.184 6 21 57 18 Strong HC13CCN, v= 0
3 9 5, 5-8 5, 4$^\star$ 81 700.966 6 47 41 13 Group detected, partial blend with U-line
5 9 6, 3-8 6, 2$^\star$ 81 702.498 5 60 33 13 Group detected, partial blend with U-line
7 9 4, 6-8 4, 5$^\star$ 81 709.838 6 35 48 13 Group detected
9 9 7, 3-8 7, 2 81 709.848 6 76 24 13 Group detected
10 9 4, 5-8 4, 4 81 710.098 6 35 48 13 Group detected
11 9 3, 7-8 3, 6 81 733.892 6 27 53 13 Detected, blend with CH3OCH3 and HCC13CN, v6 = 1
12 9 3, 6-8 3, 5 81 756.174 6 27 53 13 Detected, blend with U-line
13 9 2, 7-8 2, 6 82 224.644 7 21 57 19 Detected, uncertain baseline
14 9 1, 8-8 1, 7 83 480.894 8 17 59 17 Blend with C2H3CN, v= 0
15 10 1,10-9 1, 9 88 240.541 8 20 66 19 Strong HNCO, v= 0 and HN13CO, v= 0
16 10 0,10-9 0, 9 89 770.285 7 19 66 18 Blend with U-line
17 10 2, 9-9 2, 8 90 561.332 6 25 64 20 Detected, blend with weak C2H5CN, v13 = 1/v21 = 1
18 10 6, 4-9 6, 3$^\star$ 90 783.538 6 64 43 14 Group detected, partial blend with CH2(OH)CHO and U-line
20 10 5, 6-9 5, 5$^\star$ 90 784.281 6 50 50 14 Group detected, partial blend with CH2(OH)CHO and U-line
22 10 7, 3-9 7, 2$^\star$ 90 790.259 6 80 34 14 Group detected, blend with U-line
24 10 4, 7-9 4, 6 90 798.685 6 39 56 14 Group detected, blend with U-line
25 10 4, 6-9 4, 5 90 799.249 6 39 56 14 Group detected, blend with U-line
26 10 8, 2-9 8, 1$^\star$ 90 801.896 7 98 24 14 Blend with U-line and HC13CCN, v7 = 1
28 10 3, 8-9 3, 7 90 829.945 6 31 60 14 Detected, blend with U-line also in M?
29 10 3, 7-9 3, 6 90 868.038 6 31 60 14 Detected, partial blend with U-line
30 10 2, 8-9 2, 7 91 496.108 8 25 64 24 Detected, partial blend with CH3CN, v4 = 1 and U-line
31 10 1, 9-9 1, 8 92 700.172 8 21 66 28 Blend with U-line and CH3OCH3
32 11 1,11-10 1,10 97 015.224 8 25 72 21 Detected, partial blend with C2H5OH and CH3OCHO
33 11 0,11-10 0,10 98 548.363 8 24 73 18 Blend with C2H5CN, v= 0
34 11 2,10-10 2, 9 99 577.063 7 29 71 19 Blend with CH3OCHO, $v_{{\rm t}}$ = 1
35 11 6, 6-10 6, 5$^\star$ 99 865.516 6 68 51 14 Strong blend with C2H5OH, CCS
37 11 5, 7-10 5, 6$^\star$ 99 869.306 6 55 58 14 Strong CH3OCHO, $v_{{\rm t}}$ = 1
39 11 7, 4-10 7, 3$^\star$ 99 871.151 6 84 43 14 Strong CH3OCHO, $v_{{\rm t}}$ = 1
41 11 8, 3-10 8, 2$^\star$ 99 882.826 7 103 34 14 Strong blend with C2H5CN, v13 = 1/v21 = 1
43 11 4, 8-10 4, 7 99 890.599 6 44 63 14 Strong blend with HC13CCN, v7 = 1 and HC13CCN, v6 = 1
44 11 4, 7-10 4, 6 99 891.725 6 44 63 14 Strong blend with HC13CCN, v6 = 1 and NH2CN
45 11 9, 2-10 9, 1$^\star$ 99 898.969 8 124 24 14 Strong HCC13CN, v6 = 1
47 11 3, 9-10 3, 8 99 928.886 6 35 68 14 Detected, partial blend with NH2CN and U-line
48 11 3, 8-10 3, 7 99 990.567 7 35 68 14 Detected
49 11 2, 9-10 2, 8 100 800.876 8 29 71 20 Detected, partial blend with CH3CH3CO, v= 0 and U-line
50 11 1,10-10 1, 9 101 899.795 8 26 72 34 Detected, uncertain baseline
51 12 1,12-11 1,11 105 777.991 8 29 79 43 Detected, blend with c-C2H4O and C2H5CN, v= 0
52 12 0,12-11 0,11 107 283.142 8 29 80 24 Detected, blend with C2H5OH and U-line
53 12 2,11-11 2,10 108 581.408 7 34 77 20 Detected, weak blend with C2H5OH
54 12 6, 7-11 6, 6$^\star$ 108 948.523 6 73 60 29 Blend with C2H5CN, v= 0 and C2H5OH
56 12 7, 5-11 7, 4$^\star$ 108 952.574 6 89 53 29 Blend with C2H5OH
58 12 5, 8-11 5, 7$^\star$ 108 956.206 6 60 66 29 Group detected, blend with C2H5OH
60 12 8, 4-11 8, 3$^\star$ 108 963.964 7 108 44 29 Strong blend with HC13CCN, v7 = 1
62 12 9, 3-11 9, 2$^\star$ 108 980.660 8 128 35 29 Strong blend with HCC13CN, v6 = 1
64 12 4, 9-11 4, 8 108 985.821 6 48 71 29 Blend with HCC13CN, v7 = 1
65 12 4, 8-11 4, 7 108 987.928 6 48 71 29 Blend with HCC13CN, v7 = 1
66 1210, 2-1110, 1$^\star$ 109 001.603 10 152 24 29 Weak
68 12 3,10-11 3, 9 109 030.225 6 40 75 29 Detected, partial blend with HC3N, v4 = 1, C2H5OH, and U-line
69 12 3, 9-11 3, 8 109 125.734 7 40 75 29 Strong HC13CCN, v7 = 1
70 12 2,10-11 2, 9 110 136.314 8 34 77 24 Blend with 13CH3OH, v= 0
71 12 1,11-11 1,10 111 076.901 8 31 79 25 Detected, slightly shifted?
72 13 1,13-12 1,12 114 528.654 8 34 86 37 Detected, partial blend with U-line
73 13 0,13-12 0,12 115 977.853 50 34 86 79 Blend with CH313CH2CN, v= 0, CH3CH3CO, and C2H5CN, v= 0
74 15 7, 9-14 7, 8$^\star$ 136 200.478 6 106 78 28 Strong HC13CCN, v7 = 1
76 15 6,10-14 6, 9$^\star$ 136 204.641 5 90 84 28 Strong HC13CCN, v7 = 1
78 15 8, 7-14 8, 6$^\star$ 136 208.805 7 125 71 28 Strong HC13CCN, v7 = 1 and HC13CCN, v6 = 1
80 15 9, 6-14 9, 5$^\star$ 136 225.653 8 145 64 28 Strong HCC13CN, v6 = 1 and HCC13CN, v7 = 1
82 15 5,11-14 5,10 136 229.823 5 77 89 28 Blend with HCC13CN, v7 = 1
83 15 5,10-14 5, 9 136 230.008 5 77 89 28 Blend with HCC13CN, v7 = 1
84 1510, 5-1410, 4$^\star$ 136 248.969 10 169 55 28 Group detected, blend with U-line
86 1511, 4-1411, 3$^\star$ 136 277.600 13 195 46 28 Strong HC3N, v4 = 1 and CH3OCHO
88 15 4,12-14 4,11 136 293.271 6 65 93 28 Strong CH313CH2CN
89 15 4,11-14 4,10 136 303.599 6 65 93 28 Detected, blend with a(CH2OH)2 and CH3C3N
90 1512, 3-1412, 2$^\star$ 136 310.849 16 223 36 28 Weak, blend with CH3C3N
92 15 3,13-14 3,12 136 341.155 6 57 96 28 Detected, partial blend with U-line also in M
93 1513, 2-1413, 1$^\star$ 136 348.271 21 253 25 28 Weak, blend with U-line
95 16 7, 9-15 7, 8$^\star$ 145 284.487 30 113 86 25 Strong HC13CCN, v7 = 1
97 16 8, 8-15 8, 7$^\star$ 145 290.958 30 131 80 25 Blend with HC13CCN, v6 = 1
99 16 6,11-15 6,10$^\star$ 145 292.688 30 97 91 25 Blend with HC13CCN, v6 = 1
101 16 9, 7-15 9, 6$^\star$ 145 307.254 30 152 73 25 Strong C2H5CN, v13 = 1/v21 = 1, HCC13CN, v7 = 1, C2H3CN, v15 = 1
103 16 5,12-15 5,11 145 325.871 30 83 96 25 Group detected, uncertain baseline, partial blend with
              C2H5CN, v13 = 1/v21 = 1
104 16 5,11-15 5,10 145 326.209 30 83 96 25 Group detected, uncertain baseline, partial blend with
              C2H5CN, v13 = 1/v21 = 1
105 1610, 6-1510, 5$^\star$ 145 330.985 40 175 65 25 Group detected, uncertain baseline
107 1611, 5-1511, 4$^\star$ 145 360.684 30 201 56 25 Strong HC3N, v4 = 1
109 1612, 4-1512, 3$^\star$ 145 395.485 60 229 46 25 Blend with C3H7CN
111 16 4,13-15 4,12 145 403.421 30 72 100 25 Blend with U-line or wing of C2H5CN, v= 0
112 16 4,12-15 4,11 145 419.704 30 72 100 25 Strong C2H5CN, v= 0
113 1613, 3-1513, 2$^\star$ 145 434.928 60 260 36 25 Weak, blend with U-line
115 16 3,14-15 3,13 145 443.850 30 63 103 25 Detected, blend with C2H5CN, v= 0 and U-line
116 1614, 2-1514, 1$^\star$ 145 478.462 60 293 25 25 Weak, strong O13CS
118 16 1,15-15 1,14 147 495.789 6 55 106 31 Detected, partial blend with H3C13CN, v8 = 1
119 16 2,14-15 2,13 147 675.839 30 58 105 31 Blend with H3C13CN, v8 = 1, U-line, and CH3OCHO
120 17 7,10-16 7, 9$^\star$ 154 369.232 40 120 94 112 Strong HC13CCN, v7 = 1 and HC13CCN, v6 = 1
122 17 8, 9-16 8, 8$^\star$ 154 373.384 40 138 88 112 Strong HC13CCN, v6 = 1
124 17 6,12-16 6,11$^\star$ 154 382.222 40 104 99 112 Strong HCC13CN, v6 = 1 and HCC13CN, v7 = 1
126 17 9, 8-16 9, 7$^\star$ 154 388.904 40 159 81 112 Strong HCC13CN, v7 = 1
128 1710, 7-1610, 6$^\star$ 154 412.758 50 182 74 112 Strong HNCO, v= 0
130 17 5,13-16 5,12 154 424.604 40 90 103 112 Strong CH3OH, v= 0
131 17 5,12-16 5,11 154 425.216 40 90 103 112 Strong CH3OH, v= 0
132 1711, 6-1611, 5$^\star$ 154 443.330 60 208 66 112 Strong HC3N, v4 = 1 and CH313CH2CN
134 1712, 5-1612, 4$^\star$ 154 479.566 15 236 57 112 Strong C2H5CN, v= 0
136 17 4,14-16 4,13 154 517.470 5 79 107 112 Blend with C2H5CN, v13 = 1/v21 = 1
137 1713, 4-1613, 3$^\star$ 154 520.861 19 267 47 112 Blend with C2H5CN, v13 = 1/v21 = 1
139 17 4,13-16 4,12 154 542.406 5 79 107 112 Group detected, blend with U-line
140 17 3,15-16 3,14 154 544.046 5 70 109 112 Group detected, blend with U-line
141 1714, 3-1614, 2$^\star$ 154 566.773 25 300 36 112 Weak, strong U-line
143 1715, 2-1615, 1$^\star$ 154 617.004 33 335 25 112 Weak, strong U-line and C2H5CN, v13 = 1/v21 = 1
145 18 7,12-17 7,11$^\star$ 163 454.794 5 127 101 38 Group detected, partial blend with HC13CCN, v6 = 1
              and HCC13CN, v6 = 1
147 18 8,10-17 8, 9$^\star$ 163 456.136 6 146 96 38 Group detected, partial blend with HC13CCN, v6 = 1
              and HCC13CN, v6 = 1
149 18 9, 9-17 9, 8$^\star$ 163 470.472 8 166 90 38 Group detected, partial blend with HCC13CN,v7 = 1
151 18 6,13-17 6,12$^\star$ 163 473.305 5 111 106 38 Group detected, partial blend with HCC13CN,v7 = 1
153 1810, 8-1710, 7$^\star$ 163 494.265 9 190 83 38 Strong CH313CH2CN
155 1811, 7-1711, 6$^\star$ 163 525.533 11 216 75 38 Group detected, blend with HC3N, v4 = 1
157 18 5,14-17 5,13 163 526.183 4 97 110 38 Group detected, blend with HC3N, v4 = 1
158 18 5,13-17 5,12 163 527.171 4 97 110 38 Group detected, blend with HC3N, v4 = 1
159 1812, 6-1712, 5$^\star$ 163 563.084 14 244 66 38 Blend with C2H3CN, v15 = 2 and SO2, v= 0
161 1813, 5-1713, 4$^\star$ 163 606.161 18 274 57 38 Strong SO2, v= 0
163 18 4,15-17 4,14 163 635.326 5 86 114 38 Detected, partial blend with C3H7CN
164 18 3,16-17 3,15 163 640.468 5 78 116 38 Detected, partial blend with C3H7CN
165 1814, 4-1714, 3$^\star$ 163 654.261 24 307 47 38 Weak, blend with H13CONH2, v= 0
167 18 4,14-17 4,13 163 672.524 5 86 114 38 Strong C2H5CN, v13 = 1/v21 = 1
168 1815, 3-1715, 2$^\star$ 163 707.031 32 343 37 38 Weak, blend with CH2(OH)CHO
170 18 2,16-17 2,15 166 463.884 30 72 118 66 Blend with 13CH2CHCN
171 19 8,12-18 8,11$^\star$ 172 539.195 40 153 104 44 Strong HCC13CN, v6 = 1
173 19 7,13-18 7,12$^\star$ 172 541.207 40 135 109 44 Strong HCC13CN, v6 = 1
175 19 9,10-18 9, 9$^\star$ 172 552.010 40 174 98 44 Strong HCC13CN, v7 = 1
177 19 6,14-18 6,13$^\star$ 172 566.092 50 119 114 44 Group detected, partial blend with U-line and HCC13CN, v7 = 1
179 1910, 9-1810, 8$^\star$ 172 575.485 50 198 91 44 Strong U-line
181 1911, 8-1811, 7$^\star$ 172 607.260 60 223 84 44 Strong HC3N, v4 = 1
183 19 5,15-18 5,14 172 630.750 30 105 117 44 Strong U-line and t-HCOOH
184 19 5,14-18 5,13 172 632.382 30 105 117 44 Strong U-line and t-HCOOH
185 1912, 7-1812, 6$^\star$ 172 645.994 13 252 76 44 Blend with t-HCOOH, H13CN, and U-line
187 1913, 6-1813, 5$^\star$ 172 690.745 17 282 67 44 Strong H13CN and CH3OCHO
189 19 3,17-18 3,16 172 731.699 30 86 123 44 Blend with U-line and C2H3CN, v= 0
190 1914, 5-1814, 4$^\star$ 172 740.945 23 315 58 44 Strong C2H3CN, v= 0
192 19 4,16-18 4,15 172 756.821 30 94 121 44 Baseline problem?
193 1915, 4-1815, 3$^\star$ 172 796.183 30 351 48 44 Weak, strong HCC13CN, v7 = 1
195 19 4,15-18 4,14 172 811.041 30 94 121 44 Strong C2H5CN, v= 0
196 1916, 3-1816, 2$^\star$ 172 856.161 40 388 37 44 Weak, strong HC3N, v= 0 and HC3N, v5 = 1/v7 = 3
198 20 0,20-19 0,19 176 174.096 30 81 132 365 Noisy, partial blend with HNCO, v5 = 1 and U-line
199 23 0,23-22 0,22 201 875.876 10 108 152 138 Strong 13CH3CH2CN, v= 0
200 22 2,20-21 2,19 203 812.341 10 107 145 364 Strong C2H3CN, v= 0
201 23 2,22-22 2,21 206 652.454 9 115 151 106 Blend with C2H5CN, v= 0
202 23 8,16-22 8,15$^\star$ 208 875.040 8 189 134 160 Blend with HCC13CN, v7 = 1, CH3CH3CO, $v_{{\rm t}}$ = 1, and CH3OCHO
204 23 9,14-22 9,13$^\star$ 208 877.860 9 210 129 160 Blend with HCC13CN, v7 = 1, CH3CH3CO, $v_{{\rm t}}$ = 1, and CH3OCHO
206 23 7,17-22 7,16$^\star$ 208 896.163 7 171 139 160 Strong C2H3CN, v= 0
208 2310,13-2210,12$^\star$ 208 897.241 10 233 124 160 Strong C2H3CN, v= 0
210 2311,12-2211,11$^\star$ 208 929.064 10 259 118 160 Strong C2H3CN, v= 0
212 23 6,18-22 6,17 208 955.555 6 155 142 160 Blend with C2H3CN, v= 0 and U-line
213 23 6,17-22 6,16 208 955.797 6 155 142 160 Blend with C2H3CN, v= 0 and U-line
214 2312,11-2212,10$^\star$ 208 970.868 11 287 111 160 Strong C2H3CN, v= 0
216 23 3,21-22 3,20 209 015.508 7 121 150 160 Strong C2H5CN, v= 0 and C2H3CN, v= 0
217 2313,10-2213, 9$^\star$ 209 021.101 13 318 104 160 Strong C2H3CN, v= 0
219 2314, 9-2214, 8$^\star$ 209 078.736 16 351 96 160 Strong C2H3CN, v= 0
221 23 5,19-22 5,18 209 081.032 6 141 146 160 Strong C2H3CN, v= 0
222 23 5,18-22 5,17 209 090.124 6 141 146 160 Strong C2H3CN, v= 0
223 2315, 8-2215, 7$^\star$ 209 143.066 23 386 88 160 Weak, strong HC13CCN, v7 = 1
225 2316, 7-2216, 6$^\star$ 209 213.584 33 424 79 58 Weak, strong H2CS and C2H3CN, v15 = 1
227 23 4,20-22 4,19 209 272.189 6 130 148 58 Detected, blend CH3CH3CO, v= 0
228 2317, 6-2217, 5$^\star$ 209 289.914 46 464 69 58 Weak, blend with C2H5CN, v13 = 1/v21 = 1 and C2H3CN, v15 = 1
230 2318, 5-2218, 4$^\star$ 209 371.766 64 507 59 58 Weak, blend with C2H5OH
232 2319, 4-2219, 3$^\star$ 209 458.910 86 552 49 58 Weak, strong C2H3CN, v15 = 2 and C2H5CN, v= 0
234 23 4,19-22 4,18 209 473.790 7 130 148 58 Strong C2H3CN, v15 = 2 and CH3OCHO
235 2320, 3-2220, 2$^\star$ 209 551.156 114 599 37 58 Weak, strong C2H3CN, v11 = 1
237 23 1,22-22 1,21 209 629.913 9 113 152 45 Detected, blend with HC13CCN, v7 = 2 and HCC13CN, v7 = 2
238 2321, 2-2221, 1$^\star$ 209 648.342 146 649 25 45 Weak, blend with U-line and C2H3CN, v11 = 1
240 24 1,24-23 1,23 210 072.793 12 118 159 45 Blend with C2H5CN, v13 = 1/v21 = 1 and 13CH3CH2CN, v= 0
241 24 0,24-23 0,23 210 448.044 12 118 159 64 Strong CH3OCHO
242 23 3,20-22 3,19 211 099.150 12 122 150 33 Blend with U-lines
243 23 2,21-22 2,20 213 074.653 70 117 152 48 Strong SO2, v= 0
244 24 2,23-23 2,22 215 466.138 10 124 158 74 Strong C2H5CN, v13 = 1/v21 = 1
245 24 3,21-23 3,20 220 537.064 14 132 157 98 Strong CH3CN, v8 = 0
246 25 1,24-24 1,23 226 957.428 40 134 165 96 Strong CN absorption
247 25 9,16-24 9,15$^\star$ 227 040.487 50 230 145 96 Group detected, partial blend with CN absorption and
              CH3CH3CO, $v_{{\rm t}}$ = 1
249 25 8,18-24 8,17$^\star$ 227 045.287 50 210 149 96 Group detected, partial blend with CN absorption and
              CH3CH3CO, $v_{{\rm t}}$ = 1
251 2510,15-2410,14$^\star$ 227 055.944 50 254 139 96 Group detected, partial blend with CN absorption
253 25 7,19-24 7,18$^\star$ 227 079.847 50 191 153 96 Group detected, blend with CH2CH13CN and CH3OH, v= 0
255 2511,14-2411,13$^\star$ 227 086.424 50 280 134 96 Blend with CH2CH13CN and CH3OH, v= 0
257 25 3,23-24 3,22 227 088.938 40 142 164 96 Blend with CH2CH13CN and CH3OH, v= 0
258 2512,13-2412,12$^\star$ 227 128.728 60 308 128 96 Blend with C2H5CN, v= 0 and C2H3CN, v= 0
260 2517, 8-2417, 7$^\star$ 227 467.235 45 485 89 85 Weak, blend with CH2(OH)CHO, CH2CH13CN and
              t-C2H5OCHO
262 25 4,22-24 4,21 227 539.318 40 151 162 85 Strong HCONH2, v12 = 1 and C2H5CN, v= 0
263 2518, 7-2418, 6$^\star$ 227 555.295 63 528 80 85 Weak, strong CH3OCHO
265 26 0,26-25 0,25 227 601.595 16 138 172 85 Strong HCONH2, v= 0
266 2519, 6-2419, 5$^\star$ 227 649.239 85 572 70 85 Weak, blend with CH3OCH3
268 2520, 5-2420, 4$^\star$ 227 748.834 113 620 60 85 Weak, blend with 13CH3CH2CN, v= 0
270 2521, 4-2421, 3$^\star$ 227 853.885 147 669 49 85 Weak, strong HC13CCN, v7 = 2 and HCC13CN, v7 = 2
272 25 4,21-24 4,20 227 892.614 60 151 162 85 Strong HCC13CN, v7 = 2, C2H5OH, and HC13CCN, v7 = 2
273 25 2,23-24 2,22 231 485.527 50 138 165 40 Detected, blend with U-line?
274 26 1,25-25 1,24 235 562.532 50 145 172 131 Strong C2H3CN, v= 0
275 27 1,27-26 1,26 235 964.814 19 149 179 131 Strong 13CH3OH, v= 0
276 26 3,24-25 3,23 236 103.949 40 153 170 37 Blend with HCC13CN, v7 = 1 and C2H5CN, v13 = 1/v21 = 1
277 26 9,17-25 9,16$^\star$ 236 121.689 50 241 152 37 Blend with 13CH3CH2CN
279 26 8,19-25 8,18$^\star$ 236 131.044 50 220 156 37 Blend with CH213CHCN
281 2610,16-2510,15$^\star$ 236 134.730 50 265 147 37 Blend with CH213CHCN
283 2611,15-2511,14$^\star$ 236 164.129 60 291 142 37 Strong C2H3CN, v11 = 1 and 13CH3CH2CN, v= 0
285 26 7,20-25 7,19$^\star$ 236 173.437 60 202 160 37 Blend with C2H3CN, v11 = 1, CH213CHCN, and
              13CH3CH2CN, v= 0
287 27 0,27-26 0,26 236 182.602 18 149 179 37 Blend with CH213CHCN, 13CH3CH2CN, v= 0, and HC3N, v4 = 1
288 2612,14-2512,13$^\star$ 236 206.427 19 319 136 37 Strong SO2, v= 0
290 2613,13-2513,12$^\star$ 236 259.339 21 349 130 37 Blend with C2H5CN, v13 = 1/v21 = 1 and t-C2H5OCHO
292 26 6,21-25 6,20 236 269.491 60 186 163 37 Group detected, partial blend with t-C2H5OCHO and U-line
293 26 6,20-25 6,19 236 270.459 60 186 163 37 Group detected, partial blend with t-C2H5OCHO and U-line
294 2614,12-2514,11$^\star$ 236 321.411 23 382 123 37 Weak, blend with C2H5OH and CH313CH2CN, v= 0
296 2615,11-2515,10$^\star$ 236 391.638 27 418 115 37 Weak, blend with CH213CHCN
298 26 5,22-25 5,21 236 454.502 40 173 166 37 Blend with SO, v= 0 and 13CH3CH2CN, v= 0, baseline problem?
299 2616,10-2516, 9$^\star$ 236 469.303 35 456 107 37 Weak, blend with CH2CH13CN
301 26 5,21-25 5,20 236 481.643 40 173 166 37 Blend with CH213CHCN
302 2617, 9-2517, 8$^\star$ 236 553.897 80 496 99 37 Weak, blend with t-C2H5OCHO, 13CH3CH2CN, v= 0, and
              CH3COOH, $v_{{\rm t}}$ = 0
304 27 1,26-26 1,25 244 135.969 14 156 178 46 Blend with C2H5CN, v13 = 1/v21 = 1
305 28 1,28-27 1,27 244 585.841 21 161 186 39 Strong CH3OCHO and HCC13CN, v= 0
306 28 0,28-27 0,27 244 765.968 21 160 186 39 Detected, blend with CH313CH2CN, v= 0 and U-line
307 27 3,25-26 3,24 245 102.984 11 164 177 72 Blend with 13CH3CH2CN, v= 0
308 27 9,18-26 9,17$^\star$ 245 202.855 16 253 159 72 Blend with 13CH3CH2CN, v= 0 and U-line?
310 2710,17-2610,16$^\star$ 245 213.055 19 276 155 72 Strong CH3OH, v= 0
312 27 8,20-26 8,19$^\star$ 245 217.230 13 232 164 72 Strong CH3OH, v= 0
314 2711,16-2611,15$^\star$ 245 241.163 21 302 150 72 Blend with C2H513CN, v= 0 and C2H3CN, v15 = 1
316 27 7,21-26 7,20$^\star$ 245 268.168 11 213 167 72 Blend with HC3N, v4 = 1
318 2712,15-2612,14$^\star$ 245 283.214 24 330 144 72 Blend with C2H513CN, v= 0
320 2713,14-2613,13$^\star$ 245 336.715 26 361 138 72 Strong SO2, v= 0
322 27 6,22-26 6,21 245 378.722 10 197 170 72 Group detected, blend with 13CH3CH2CN, v= 0?
323 27 6,21-26 6,20 245 380.146 10 197 170 72 Group detected, blend with 13CH3CH2CN, v= 0?
324 2714,13-2614,12$^\star$ 245 400.026 29 394 131 72 Blend with U-line, CH3CH3CO, v= 0 and 13CH3CH2CN, v= 0?
326 2715,12-2615,11$^\star$ 245 472.024 33 429 124 72 Weak, strong C2H5CN, v13 = 1/v21 = 1 and C2H3CN, v11 = 1
328 2716,11-2616,10$^\star$ 245 551.911 40 467 116 53 Weak, blend with SO2, v= 0
330 27 5,23-26 5,22 245 585.766 10 184 173 53 Strong CH213CHCN and HC3N, v= 0
331 27 5,22-26 5,21 245 623.711 10 184 173 53 Strong HC3N, v5 = 1/v7 = 3 and CH213CHCN
332 2717,10-2617, 9$^\star$ 245 639.099 51 507 108 53 Weak, blend with C2H3CN, v15 = 2
334 2718, 9-2618, 8$^\star$ 245 733.144 67 550 100 53 Weak, strong HNCO, v5 = 1
336 27 4,24-26 4,23 245 803.548 10 173 175 53 Blend with CH2CH13CN
337 2719, 8-2619, 7$^\star$ 245 833.697 88 595 91 53 Weak, strong U-line, partial blend with CH2CH13CN and
              C2H3CN, v11 = 1/v15 = 1
339 2720, 7-2620, 6$^\star$ 245 940.476 116 642 81 53 Weak, strong U-line and CH3OCHO, $v_{{\rm t}}$ = 1
341 2721, 6-2621, 5$^\star$ 246 053.247 150 692 71 53 Weak, strong CH3OCHO
343 28 3,26-27 3,25 254 085.051 12 176 184 32 Blend with CH3CH3CO, v= 0 and C2H5CN, v= 0
344 28 9,19-27 9,18$^\star$ 254 283.930 19 264 167 32 Strong SO2, v= 0 and 13CH3OH, v= 0
346 2810,18-2710,17$^\star$ 254 290.939 22 288 162 32 Strong SO2, v= 0, 13CH3OH, v= 0, 13CH2CHCN,
              13CH3CH2CN, v= 0, and H13CONH2, v12 = 1
348 28 8,21-27 8,20$^\star$ 254 303.873 15 244 171 32 Blend with 13CH3CH2CN, v= 0 and C2H5CN, v= 0
350 2811,17-2711,16$^\star$ 254 317.460 26 314 157 32 Strong C2H5CN, v= 0 and 13CH3OH, v= 0
352 2812,16-2712,15$^\star$ 254 359.074 29 342 152 32 Blend with H13CONH2, v= 0
354 28 7,22-27 7,21$^\star$ 254 364.160 12 225 174 32 Blend with H13CONH2, v= 0
356 2813,15-2713,14$^\star$ 254 413.004 32 372 146 32 Strong C2H5CN, v= 0, H13CONH2, v= 0, and CH3OH, v= 0
358 2822, 6-2722, 5$^\star$ 255 273.081 196 755 71 217 Weak, strong 13CH3OH, v= 0 and CH2CH13CN
360 2823, 5-2723, 4$^\star$ 255 401.564 245 809 60 217 Weak, blend with CH3CH3CO, $v_{{\rm t}}$ = 1
362 2824, 4-2724, 3$^\star$ 255 535.733 304 866 49 217 Weak, blend with SO2, v= 0 and U-line?
364 28 4,24-27 4,23 255 674.369 18 185 182 217 Strong HC3N, v7 = 1
365 2825, 3-2725, 2$^\star$ 255 675.432 372 925 38 217 Strong HC3N, v7 = 1
367 28 2,26-27 2,25 258 775.885 19 172 185 1609 Weak, blend with CH3OH, v= 0
368 29 9,20-28 9,19$^\star$ 263 364.923 22 277 174 74 Group detected, baseline problem?, blend with U-line
370 2910,19-2810,18$^\star$ 263 368.355 26 300 170 74 Group detected, baseline problem?, blend with U-line
372 29 8,22-28 8,21$^\star$ 263 390.982 17 256 178 74 Blend with HNCO, v4 = 1 and CH3OCH3
374 2911,18-2811,17$^\star$ 263 393.008 31 326 165 74 Blend with HNCO, v4 = 1 and CH3OCH3
376 2912,17-2812,16$^\star$ 263 433.971 35 354 160 74 Strong HC3N, v4 = 1, HNCO, v5 = 1, and HNCO, v= 0
378 29 7,23-28 7,22$^\star$ 263 461.436 14 237 181 74 Blend with HNCO, v= 0, CH3CH3CO, v= 0 and C2H5OH
380 2913,16-2813,15$^\star$ 263 488.164 40 385 154 74 Blend with C2H513CN, v= 0
382 2914,15-2814,14$^\star$ 263 553.566 44 418 148 74 Strong SO2, v= 0, HCONH2, v12 = 1, and CH2(OH)CHO
384 29 6,24-28 6,23 263 604.573 12 221 184 74 Group detected, baseline problem?, partial blend with
              CH3CH3CO, $v_{{\rm t}}$ = 1 and CH3OCH3
385 29 6,23-28 6,22 263 607.689 12 221 184 74 Group detected, baseline problem?, partial blend with
              CH3CH3CO, $v_{{\rm t}}$ = 1 and CH3OCH3
386 2915,14-2815,13$^\star$ 263 628.792 50 453 141 74 Strong CH3OCH3
388 2916,13-2816,12$^\star$ 263 712.865 57 491 134 108 Weak, strong HCC13CN, v7 = 1 and HNCO, v6 = 1
390 2917,12-2817,11$^\star$ 263 805.068 67 531 126 108 Weak, strong HC3N, v5 = 1/v7 = 3 and C2H5CN, v= 0
392 29 5,25-28 5,24 263 857.842 12 208 187 108 Blend with HCONH2, v= 0 and C2H513CN, v= 0
393 2918,11-2818,10$^\star$ 263 904.858 81 574 118 108 Weak, blend with SO2, v= 0, C2H5CN, v13 = 1/v21 = 1, and U-line?
395 29 5,24-28 5,23 263 928.994 13 208 187 108 Blend with C2H5CN, v13 = 1/v21 = 1 and C2H5CN, v= 0
396 2919,10-2819, 9$^\star$ 264 011.816 101 619 110 108 Weak, strong CH313CH2CN, v= 0
398 29 4,26-28 4,25 264 055.836 13 197 189 108 Detected, partial blend with C2H5CN, v= 0 and
              CH3CH3CO, v= 0
a Numbering of the observed transitions with $S\mu ^2$ > 20 D2.
b Transitions marked with a $^\star$ are double with a frequency difference less than 0.1 MHz. The quantum numbers of the second one are not shown.
c Frequency uncertainty.
d Lower energy level in temperature units ( $E_{\rm l}/$$k_{\rm B}$).
e Calculated rms noise level in $T_{{\rm mb}}$ scale.


  \begin{figure}
\par\includegraphics[angle=270,width=7.5cm,clip]{9203f101.ps}\hsp...
...ce*{0.5cm}
\includegraphics[angle=270,width=7.3cm,clip]{9203f108.ps}\end{figure} Figure 1: Transitions of amino acetonitrile (AAN) detected with the IRAM 30 m telescope. Each panel consists of two plots and is labeled in black in the upper right corner. The lower plot shows in black the spectrum obtained toward Sgr B2(N) in main-beam temperature scale (K), while the upper plot shows the spectrum toward Sgr B2(M). The rest frequency axis is labeled in GHz. The systemic velocities assumed for Sgr B2(N) and (M) are 64 and 62 km s-1, respectively. The lines identified in the Sgr B2(N) spectrum are labeled in blue. The top red label indicates the AAN transition centered in each plot (numbered like in Col. 1 of Table 3), along with the energy of its lower level in K ( $E_{\rm l}/k_{{\rm B}}$). The other AAN lines are labeled in blue only. The bottom red label is the feature number (see Col. 8 of Table 3). The green spectrum shows our LTE model containing all identified molecules, including AAN. The LTE synthetic spectrum of AAN alone is overlaid in red, and its opacity in dashed violet. All observed lines which have no counterpart in the green spectrum are still unidentified in Sgr B2(N).


 \begin{figure}
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...e*{0.5cm}
\includegraphics[angle=270,width=7.3cm,clip]{9203f116.ps}
\end{figure} Figure 1: continued.


 \begin{figure}
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...e*{0.5cm}
\includegraphics[angle=270,width=7.3cm,clip]{9203f124.ps}
\end{figure} Figure 1: continued.


 \begin{figure}
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\includegraphics[angle=270,width=7.3cm,clip]{9203f132.ps}
\end{figure} Figure 1: continued.


 \begin{figure}
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...e*{0.5cm}
\includegraphics[angle=270,width=7.3cm,clip]{9203f140.ps}
\end{figure} Figure 1: continued.


 \begin{figure}
\par\includegraphics[angle=270,width=7.5cm,clip]{9203f141.ps}
\end{figure} Figure 1: continued.



Copyright ESO 2008