EDP Sciences
Free Access
Issue
A&A
Volume 594, October 2016
Article Number A115
Number of page(s) 4
Section Stellar structure and evolution
DOI https://doi.org/10.1051/0004-6361/201527911
Published online 20 October 2016

© ESO, 2016

1. Introduction

IRAS 085894714 (RA, Dec.(J2000) = 09:00:40.5, –47:25:55)can be classified as an ultracompact Hii region (UCHII) according to the criteria by Wood & Churchwell (1989). This source coincides with a massive dust clump detected in the IR continuum at 1.2 mm by Beltrán et al. (2006). They estimated a luminosity of 1.8 × 103L and a mass of 40 M for this object.

Wouterloot & Brand (1989) detected emission in the 12CO(10) molecular line (angular resolution: 43′′) toward the IRAS source at VLSR = + 5.2 km s-1. The molecular line shows an asymmetry in the blueshifted peak that is likely produced by noncentral self-absorption and a wing extended toward the red, which is a tracer of a potential outflow. Bronfman et al. (1996) observed the source in the CS(21) molecular line at VLSR = + 4.3 km s-1, and Urquhart et al. (2014) detected emission from the high density ammonium molecular tracer. The central velocity coincides with that of the CS line. With velocities in the range 45 km s-1, the circular galactic rotation model by Brand & Blitz (1993) predicts a kinematical distance of 2.0 kpc. An uncertainty of 0.5 kpc is assumed, adopting a velocity dispersion of 2.5 km s-1 for the interstellar molecular gas.

We report molecular line observations of the IRAS source using tracers of low and high density regions with the aim of studying the molecular gas content of the source, identifying dense gas clumps, finding massive young stellar objects (YSOs) linked to the clumps, and identifying possible outflows.

2. Molecular line observations

IRAS 085894714 was observed with the 12 m Atacama Pathfinder EXperiment (APEX) telescope1, located in Llano de Chajnantor, in the Puna de Atacama, Chile. We carried out observations in the 12CO(32), 13CO(32), C18O(32), HCO+(32), and HCN(32) molecular lines using the On-The-Fly mapping technique. These observations were made on 2014 June 16, 19, and 21. The CO isotopes were observed with the receiver APEX2 in the spectral range of 343.8347.8 GHz and in the range 328.6332.6 GHz with a half-power beamwidth of ~18′′, while the HCO+ and HCN molecules were observed with the receiver APEX1 in the spectral range of 265.6269.5 GHz with an HPBW of ~22′′ (Vassilev et al. 2008).

thumbnail Fig. 1

Spectra of the 12CO(32), 13CO(32), and C18O(32) lines indicated in black, red, and blue, respectively. Each spectrum is the average of the profiles within a field of 25.̋5 × 25.̋5. The total area is 150′′× 150′′ for three molecules. The locations of sources 1 (S1) and 3 (S3) are labeled. In each panel the velocity ranges from 4 to +15 km s-1 and Tmb scales from 2 to 18 K.

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We mapped an area of 150′′× 150′′ covering the central region of the IRAS source and the 1.2 mm emission zone detected by Beltrán et al. (2006). The APEX1 system temperature is 150 K and 300 K for APEX2. The data reduction was performed according to the standard procedure of the CLASS software, Gildas2. The antenna temperature, TA, was transformed to main-beam brightness-temperature (Tmb = TA/ηmb), using a main beam efficiency ηmb = 0.72 for APEX1 and APEX2 (Vassilev et al. 2008).The data were obtained with a velocity resolution of 0.11 km s-1. The final rms is 0.3 K.

3. Identification of YSOs

To investigate the presence of YSOs coincident with the IRAS source in the Wide-field Infrared Survey Explorer (WISE) catalog (Wright et al. 2010), we applied the following criteria (Koenig et al. 2012). Class I objects are those that satisfy W1 − W2 > 1.0 and W2 − W3 > 2.0, whereas Class II objects have W1 − W2 − σ1> 0.25 and W2 − W3 − σ2> 1.0, where W1, W2, W3, and W4 are the magnitudes in the four WISE bands at 3.4, 4.6, 12, and 22 μm, respectively, and σ1 and σ2 are the combined errors of W1 − W2 and W2 − W3, respectively3. Three sources with colors of Class I/II were identified. Their coordinates and correlation with 2MASS sources are indicated in Table 1. Sources 1 and 3 are projected onto the dust clump detected by Beltrán et al. (2006).

4. Molecular line analysis

4.1. The 12CO, 13CO, and C18O molecular tracers

Figure 1 shows the spectra corresponding to the 12CO(32), 13CO(32), and C18O(32) molecular lines (indicated in black, red, and blue colors, respectively). In this figure we distinguish two areas in the 12CO molecular emission: for Δα> − 40′′, the emission is very complex and shows many components with velocities between 3.0 and +13 km  s-1, while for Δα< − 40′′ the emission is weak, below 3 K.

The profiles of the 13CO(32) line reveal two distinct regions, as in the case of the 12CO emission. The emission in the 13CO(32) spectra has velocities in the range [+1, +9]  km s-1 and only one maximum that is centered between ~+4 and +5 km s-1. The C18O(32) line profiles are shown in the same area than in the previous cases. The area of more intense emission has a rather elongated shape from NE to SW.

thumbnail Fig. 2

Left panels: molecular line profiles of 12CO, 13CO, C18O, HCO+, and HCN toward source 1. The vertical dashed central line corresponds to +4.6 km s-1. The two remaining vertical dashed lines indicate the velocity range [+2.7, +6.3] km s-1. Integrated emission maps for the observed molecules (green contours) superposed over the 4.6 μm (grayscale) image. The range of the integrated emission for all molecules is [+2.7,+6.3] km s-1. The contour levels of the 13CO are between 4 and 47 K km s-1. The contour levels of C18O have values between 1.9 and 13.2 K km s-1, while the contours of HCO+ and HCN are between 0.87.8 K km s-1 and 1.14.1 K km s-1, respectively. Herschel maps at 500 a), 350 b), 250 c), and 70 μm d) are superimposed in white contours. The white cross indicates the IRAS source position, and the red arrows indicate the location of the identified sources. The HPBW is shown in the lower right corner of each panel. Right panels: molecular line profiles toward source 3. The vertical dashed central line corresponds to +4.0 km s-1. Integrated emission maps of the observed molecules (green contours) superposed onto the 4.6 μm (grayscale) image. The integration range for all molecules is [+3.0, +4.0] km s-1. The velocity range is indicated by the green bar. The contour levels of the CO are between 6.4 and 8.0 K km s-1. The contours levels of 13CO have values between 4.5 and 6.5 K km s-1, while the contours of C18O and HCO+ are between 1.22.3 K km s-1 and 0.71.1 K km s-1, respectively.

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Table 1

Candidate YSOs in the WISE and 2MASS databases detected toward IRAS 085894714.

4.2. Molecular emission toward sources 1 and 3

Figure 2 shows the spectra of the molecular lines observed toward sources 1 and 3 indicated in Fig. 1. Toward source 1(see the two panels on the left of Fig. 2), the 12CO(32) emission consists of three maxima between ~0.0 and ~+12.0 km s-1 that are centered at ~+2.2, +3.6, and +6.3 km s-1. The profile shows a strong broadening toward more positive velocities and weaker broadening toward more negative velocities (all velocities are referred to the local standard of rest).

The spectra of the remaining molecules display emission between the two external dashed lines (+ 2.7 < V < + 6.3 km s-1) with the exception of the 13CO(32) and HCN(32) lines, which show weak emission outside this velocity interval. The 13CO(32) and C18O(32) lines show peak temperatures at the same velocity of a depression in the 12CO(32) profile, which is a characteristic shared by the HCO+(32) and HCN(32) spectra.

Considering that the emission of HCO+(32) and HCN(32) corresponds to the densest region of the molecular cloud, we adopt V = + 4.6 km s-1 as the systemic velocity, Vsys, for the molecular counterpart of source 1 (central dashed line in Fig. 2), in agreement with Bronfman et al. (1996).

The second panel on the left of Fig. 2also shows the spatial distribution of the molecular gas emission in the 13CO(32), C18O(32), HCO+(32), and HCN(32) lines (green contours), integrated within the velocity range enclosed by the two external dashed lines in the first panel. The molecular emission is superposed onto the 4.6 μm image (grayscale) and onto Herschel at 500 (a), 350 (b), 250 (c), and 70 μm (d) in white contours. The emission of the molecular lines shows a maximum coincident with the brightest region in the far-IR, and the extension of the emission decreases in size from 13CO(32) to HCN(32). The dust emission provides evidence for a similar trend from 500 to 70 μm. The spatial agreement between the line and the continuum emissions reveals the molecular counterpart of the dust clump. The HCO+ and HCN emission shows a dense molecular region inside a lower density clump depicted by the 12CO and 13CO emissions. The molecular emission covers a region with an equivalent radius of 50′′.

Figure 2 also shows the molecular line spectra toward source 3(see the two panels on the right). The 12CO(32) spectrum shows emission between ~2.0 to ~+13.0 km s-1 with four peaks. The central velocity of the second peak (~+3.6 km s-1) is in agreement with the maximum in the remaining molecular spectra (~+4.0 km s-1), whose emission is enclosed by the two external dashed lines, between +2.7 and +5.3 km s-1.

The spatial distribution of theemission in the 12CO(32), 13CO(32), C18O(32), and HCO+(32) lines (green contours) toward source 3 is also shown in Fig. 2, integrated in the range [+3.0, +4.0] km s-1, and overlaid onto the 4.6 μm image (grayscale). This small velocity interval was chosen to highlight the gas linked to source 3,although the molecular emission linked to this source is detected in the velocity interval [+2.7, +5.3] km s-1. Both sources 1 and 3 are buried in the same molecular clump. The detection of HCO+(32) toward source 3 also reveals the presence of dense molecular gas, which is linked to this source.

4.3. Physical parameters of the molecularclump

From the 13CO(32) and C18O(32) emission lines toward source 1 and 3, we determine the optical depth of each molecule (τ13 and τ18), excitation temperature (Tex), column density and mass of the molecularclump linked to both sources. The excitation temperature was derived assuming local thermodynamic equilibrium (LTE) conditions and that the emission in the 13CO(32) line is optically thick (τ13CO ≫ 1). Using the equations by Buckle et al. (2010), the excitation temperature result is 19.3 K. Assuming that Tex is the same for the two isotopologues, we estimate optical depths for C18O and 13CO as 0.6 and 3.2, respectively.

From the C18O column density we estimate the mass as (1)where [H2/C18O] = 6 × 106 (Frerking et al. 1982) is themolecular hydrogen-carbon monoxide abundance and A is the area of the clump. From the C18O(32) contours of Fig. 2, we adopt an equivalent radius of 50′′ (or 0.45 pc at 2.0 kpc) for the molecular clump linked to the sources. Adopting values for ΔV13 and ΔV18 of 2.25 and 1.5 km s-1, respectively, we estimate an H2 column density of 1.4 × 1022 cm-2 and a mass of 310 M. A volume density nH2 ~ 1.2 × 104 cm-3 is derived by distributing the molecular mass within a sphere of 0.45 pc in radius. Masses and H2 volume densities are within the values derived for clumps in other regions of the Galaxy.

The detection of HCO+ and HCN toward sources 1 and 3 indicates regions with high ambient densities with values of up to the critical density of the HCO+ line (3 × 106 cm-3).

4.4. Virial mass

The virial mass of the clump can be obtained from the C18O(32) line. Considering only gravitational and internal pressure (i.e., neglecting support of magnetic fields, internal heating sources, or external pressure) and assuming a spherically symmetric cloud with an r-2 density distribution, the virialized molecular mass of the whole clump, Mvir, can be estimated from Mvir = 126 Reffvcl)2 (MacLaren et al. 1988). In this expression, is the effective radius in parsecs, Acl is the area of the clump, and Δvcl is the width of the composite spectrum, which is defined in the same manner as for ΔV18 in Fig. 2. We find that the virial mass is ~135 M, which is much less than the LTE mass (310 M); this suggests that the clump is collapsing. This result is compatible with the presence of embedded YSOs.

5. Molecular outflows

Figure 3 shows the position-velocity diagrams of the 12CO(32) line emission along a cut from the northeast to southwest direction passing through the positions of sources 1 and 3, where the offset position 0.0′′ corresponds to the spectra through the center of source 1. The brightest emission, with velocities in the range ~+2.7 <v< + 5.0 km s-1, within the outer dashed lines in Fig. 2, corresponds to the clump. Figure 3 reveals molecular gas with velocities that are larger than those of the molecular turbulence (+2.5 km s-1) outside the mentioned velocity range. The cut shows a prominent redshifted emission from ~+5.5 to +10 km s-1, labeled as O-s1, and a less notorious emission from ~+6.0 to +8.5 km s-1, indicated as O-s3 in white. This emission is overlapped by a cloud (O-sZ) showed in the velocity range ~+9.5 <V< + 13.0 km s-1. However, this particular emission might also be considered as asmall cloud that is extended from ~+6.0 to +13.0 km s-1 and connected to source 3. For blueshifted velocities, the extended emission is clearly detectable from ~1.5  to  +2.7 km s-1 and from 0.0 to +2.7 km s-1. These emissions would be associated with the redshifted emission O-s3 and O-s1, respectively.

thumbnail Fig. 3

Position-velocity diagrams of the 12CO(3 − 2) molecular emission along a line from the northeast to southwest direction through the sources 1 and 3. Contour levels correspond to 1.5, 2.3, 3.5, 5.0, 7.0, 9.0, 11.0, and 14.0 K. Emissions labeled as O-s1 and O-s3 would be the redshifted and blueshifted lobes associated with sources 1 and 3, respectively.

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The outflowing gas is generally shown by an optically thick line (such us 12CO), while the central clump is detected in an optically thin line (such as C18O). Bearing in mind the 12CO(32) and C18O(32) lines (Fig. 2) , we take into account that, for source 1, the blue and red wings are defined in the velocity intervals [0.0, +2.7] and [+5.5, +10] km s-1, respectively, while for source 3, these intervals are [–1.5, +2.7] and [+6.0, +13] km s-1. We believe that molecular material with velocities outside the two dashed lines can be explained as molecular outflows originated in sources 1 and 3.

In Fig. 4 we show the integrated emission of the CO line within the redshifted and blueshifted velocity intervals indicated above. Four structures can be distinguished in blueshifted velocities, two of these are over sources 1 and 3 (O-s1 and O-s3) and the other two are labeled as O-sX and O-sY. In redshifted velocities, we find extended molecular emission peaking on sources 1 and toward source 3. On the contrary, no clear redshifted velocity component is associated with O-sX and/or O-sY. O-sX might be linked to the blueshifted outflows of one of the sources (see Fig. 4), since emission with the velocity range of this component is detected toward both sources in 12CO and 13CO.

thumbnail Fig. 4

Integrated map emission of the 12CO(32) line wing profiles toward sources 1 and 3 superposed onto the 4.6 μm WISE image (grayscale). Light blue contours correspond to 7, 10, 12, 14, and 16 K km s-1,  while red contours correspond to 18, 24, 32, 40, 45, and 48 K km s-1.

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Table 2

Parameters of the molecular outflows from the 12CO(32) line.

Adopting an abundance of [12CO/13CO] = 74 for a galactocentric distance of 8.8 kpc (Wilson & Rood 1994), we estimate the opacities for the gas in the molecular outflows. Since the blueshifted lobes are not detected at 13CO(32), we adopt the same optical depths as for the redshifted lobes. Excitation temperatures are ~15 K for both outflows. Table 2 summarizes the optical depths for redshifted lobes, the effective diameters φ, the velocity width of each lobe, and the masses of the blueshifted and redshifted lobes.The detection of outflows is compatible with previous findings by Wouterloot & Brand (1989).

6. Summary

IRAS 085894714 was observed in five molecular lines with the APEX telescope to characterize the molecular environment. An area of ~150′′× 150′′, centered on the IRAS source position, was covered in the (32) transition of 12CO, 13CO, C18O, HCO+, and HCN lines. A search for candidate YSOs in the WISE database allowed us to identify three IR point sources with characteristics of Class I/II objects according to the criteria by Koenig et al. (2012) within the surveyed region.

The molecular line profiles of 12CO, 13CO, and C18O, show multiple velocity components and strong broadening effects toward sources 1 and 3. The spatial distribution of the CO emission shows the presence of a molecular clump of 0.45 pc in radius with mass and H2 volume density of 310 M and 1.4 × 104 cm-3, respectively. The comparison between the LTE and virial mass indicates that the clump is collapsing. The HCO+ and HCN spectra reveal molecular overdensities that are coincident with sources 1 and 3. Finally, we detect two possible outflows associated with each source.


1

Atacama Pathfinder EXperiment. APEX is a collaboration between the Max-Planck-Institut fur Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory.

Acknowledgments

We thank Ramiro Franco for coordinating the observations with the APEX telescope. H.P.S. acknowledges financial support from a fellowship from CONICET. This project was partially financed by CONICET of Argentina under projects PIP 00356, and PIP 00107 and from UNLP, projects PPID092, PPID/G002, and 11/G120. M.R. wishes to acknowledge support from CONICYT (CHILE) through FONDECYT grant No 1140839.

References

All Tables

Table 1

Candidate YSOs in the WISE and 2MASS databases detected toward IRAS 085894714.

Table 2

Parameters of the molecular outflows from the 12CO(32) line.

All Figures

thumbnail Fig. 1

Spectra of the 12CO(32), 13CO(32), and C18O(32) lines indicated in black, red, and blue, respectively. Each spectrum is the average of the profiles within a field of 25.̋5 × 25.̋5. The total area is 150′′× 150′′ for three molecules. The locations of sources 1 (S1) and 3 (S3) are labeled. In each panel the velocity ranges from 4 to +15 km s-1 and Tmb scales from 2 to 18 K.

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In the text
thumbnail Fig. 2

Left panels: molecular line profiles of 12CO, 13CO, C18O, HCO+, and HCN toward source 1. The vertical dashed central line corresponds to +4.6 km s-1. The two remaining vertical dashed lines indicate the velocity range [+2.7, +6.3] km s-1. Integrated emission maps for the observed molecules (green contours) superposed over the 4.6 μm (grayscale) image. The range of the integrated emission for all molecules is [+2.7,+6.3] km s-1. The contour levels of the 13CO are between 4 and 47 K km s-1. The contour levels of C18O have values between 1.9 and 13.2 K km s-1, while the contours of HCO+ and HCN are between 0.87.8 K km s-1 and 1.14.1 K km s-1, respectively. Herschel maps at 500 a), 350 b), 250 c), and 70 μm d) are superimposed in white contours. The white cross indicates the IRAS source position, and the red arrows indicate the location of the identified sources. The HPBW is shown in the lower right corner of each panel. Right panels: molecular line profiles toward source 3. The vertical dashed central line corresponds to +4.0 km s-1. Integrated emission maps of the observed molecules (green contours) superposed onto the 4.6 μm (grayscale) image. The integration range for all molecules is [+3.0, +4.0] km s-1. The velocity range is indicated by the green bar. The contour levels of the CO are between 6.4 and 8.0 K km s-1. The contours levels of 13CO have values between 4.5 and 6.5 K km s-1, while the contours of C18O and HCO+ are between 1.22.3 K km s-1 and 0.71.1 K km s-1, respectively.

Open with DEXTER
In the text
thumbnail Fig. 3

Position-velocity diagrams of the 12CO(3 − 2) molecular emission along a line from the northeast to southwest direction through the sources 1 and 3. Contour levels correspond to 1.5, 2.3, 3.5, 5.0, 7.0, 9.0, 11.0, and 14.0 K. Emissions labeled as O-s1 and O-s3 would be the redshifted and blueshifted lobes associated with sources 1 and 3, respectively.

Open with DEXTER
In the text
thumbnail Fig. 4

Integrated map emission of the 12CO(32) line wing profiles toward sources 1 and 3 superposed onto the 4.6 μm WISE image (grayscale). Light blue contours correspond to 7, 10, 12, 14, and 16 K km s-1,  while red contours correspond to 18, 24, 32, 40, 45, and 48 K km s-1.

Open with DEXTER
In the text

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