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ATLASGAL-selected massive clumps in the inner Galaxy: II. Characterisation of different evolutionary stages and their SiO emission

Csengeri, T., Leurini, S., Wyrowski, F., Urquhart, J.S., Menten, K.M., Walmsley, M., Bontemps, S., Wienen, M., Beuther, H., Motte, F., and others. (2016) ATLASGAL-selected massive clumps in the inner Galaxy: II. Characterisation of different evolutionary stages and their SiO emission. Astronomy and Astrophysics, 586 . ISSN 0004-6361. (doi:10.1051/0004-6361/201425404) (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided) (KAR id:55234)

The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided.
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Context. The processes leading to the birth of high-mass stars are poorly understood. The key first step to reveal their formation processes is characterising the clumps and cores from which they form.

Aims. We define a representative sample of massive clumps in different evolutionary stages selected from the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL), from which we aim to establish a census of molecular tracers of their evolution. As a first step, we study the shock tracer, SiO, mainly associated with shocks from jets probing accretion processes. In low-mass young stellar objects (YSOs), outflow and jet activity decreases with time during the star formation processes. Recently, a similar scenario was suggested for massive clumps based on SiO observations. Here we analyse observations of the SiO (2?1) and (5?4) lines in a statistically significant sample to constrain the change of SiO abundance and the excitation conditions as a function of evolutionary stage of massive star-forming clumps.

Methods. We performed an unbiased spectral line survey covering the 3-mm atmospheric window between 84?117 GHz with the IRAM 30 m telescope of a sample of 430 sources of the ATLASGAL survey, covering various evolutionary stages of massive clumps. A smaller sample of 128 clumps has been observed in the SiO (5?4) transition with the APEX telescope to complement the (2?1) line and probe the excitation conditions of the emitting gas. We derived detection rates to assess the star formation activity of the sample, and we estimated the column density and abundance using both an LTE approximation and non-LTE calculations for a smaller subsample, where both transitions have been observed.

Results. We characterise the physical properties of the selected sources, which greatly supersedes the largest samples studied so far, and show that they are representative of different evolutionary stages. We report a high detection rate of >75% of the SiO (2?1) line and a >90% detection rate from the dedicated follow-ups in the (5?4) transition. Up to 25% of the infrared-quiet clumps exhibit high-velocity line wings, suggesting that molecular tracers are more efficient tools to determine the level of star formation activity than infrared colour criteria. We also find infrared-quiet clumps that exhibit only a low-velocity component (FWHM ~ 5?6 km s-1) SiO emission in the (2?1) line. In the current picture, where this is attributed to low-velocity shocks from cloud-cloud collisions, this can be used to pinpoint the youngest, thus, likely prestellar massive structures. Using the optically thin isotopologue (29SiO), we estimate that the (2?1) line is optically thin towards most of the sample. Furthermore, based on the line ratio of the (5?4) to the (2?1) line, our study reveals a trend of changing excitation conditions that lead to brighter emission in the (5?4) line towards more evolved sources. Our models show that a proper treatment of non-LTE effects and beam dilution is necessary to constrain trends in the SiO column density and abundance.

Conclusions. We conclude that the SiO (2?1) line with broad line profiles and high detection rates is a powerful probe of star formation activity in the deeply embedded phase of the evolution of massive clumps. The ubiquitous detection of SiO in all evolutionary stages suggests a continuous star formation process in massive clumps. Our analysis delivers a more robust estimate of SiO column density and abundance than previous studies and questions the decrease of jet activity in massive clumps as a function of age. The observed increase of excitation conditions towards the more evolved clumps suggests a higher pressure in the shocked gas towards more evolved or more massive clumps in our sample.

Item Type: Article
DOI/Identification number: 10.1051/0004-6361/201425404
Additional information: Unmapped bibliographic data: C7 - A149 [EPrints field already has value set] LA - English [Field not mapped to EPrints] J2 - Astron. Astrophys. [Field not mapped to EPrints] AD - Max Planck Institute for Radioastronomy, Auf dem Hügel 69, Bonn, Germany [Field not mapped to EPrints] AD - INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, Firenze, Italy [Field not mapped to EPrints] AD - Dublin Institute for Advanced Studies, Burlington Road 10, Dublin 4, Ireland [Field not mapped to EPrints] AD - OASU/LAB-UMR5804, CNRS, Université Bordeaux 1, Floirac, France [Field not mapped to EPrints] AD - Max Planck Institute for Astronomy, Königstuhl 17, Heidelberg, Germany [Field not mapped to EPrints] AD - Laboratoire AIM Paris Saclay, CEA-INSU/CNRS-Université Paris Diderot, IRFU/SAp CEA-Saclay, Gif-sur-Yvette, France [Field not mapped to EPrints] AD - National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, Japan [Field not mapped to EPrints] AD - Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON, Canada [Field not mapped to EPrints] AD - I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, Köln, Germany [Field not mapped to EPrints] AD - European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile [Field not mapped to EPrints] AD - Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille), UMR 7326, Marseille, France [Field not mapped to EPrints] AD - Dipartimento di Fisica, Universitá di Cagliari, Strada Prov.le Monserrato-Sestu Km 0.700, Monserrato, CA, Italy [Field not mapped to EPrints] DB - Scopus [Field not mapped to EPrints] M3 - Article [Field not mapped to EPrints]
Uncontrolled keywords: ISM: abundances, ISM: jets and outflows, stars: formation, stars: massive, surveys
Subjects: Q Science > QB Astronomy > QB460 Astrophysics
Divisions: Divisions > Division of Natural Sciences > Physics and Astronomy
Depositing User: James Urquhart
Date Deposited: 04 May 2016 13:22 UTC
Last Modified: 17 Aug 2022 12:20 UTC
Resource URI: (The current URI for this page, for reference purposes)

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