Astronomy & Astrophysics

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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. Müller^{1, 2}, P. Schilke¹, J. Ott^{3, 4, 5}, S. Thorwirth¹, and C. Hieret¹

¹ Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
    e-mail: [belloche;kmenten;ccomito;schilke;sthorwirth;chieret]@mpifr-bonn.mpg.de
² I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
    e-mail: hspm@ph1.uni-koeln.de
³ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA
    e-mail: jott@nrao.edu
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 $\arcsec$ (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 $\times$ 10^12-14 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

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