The RMS Survey: Ammonia mapping of the environment of massive young stellar objects

Abstract

We present the results of ammonia observations towards 66 massive star forming regions identified by the Red MSX source survey. We have used the Green Bank Telescope and the K-band focal plane array to map the ammonia NH3 (1,1) and (2,2) inversion emission at a resolution of 30 arcsec in 8 arcmin regions towards the positions of embedded massive star formation. We have identified a total of 115 distinct clumps, approximately two-thirds of which are associated with an embedded massive young stellar object or compact HII region, while the others are classified as quiescent. There is a strong spatial correlation between the peak NH3 emission and the presence of embedded objects. We derive the spatial distribution of the kinetic gas temperatures, line widths, and NH${}_3$ column densities from these maps, and by combining these data with dust emission maps we estimate clump masses, H${}_2$ column densities and ammonia abundances. The clumps have typical masses of ~1000 Msun and radii ~0.5 pc, line widths of ~2 km/s and kinetic temperatures of ~16-20 K. We find no significant difference between the sizes and masses of the star forming and quiescent subsamples; however, the distribution maps reveal the presence of temperature and line width gradients peaking towards the centre for the star forming clumps while the quiescent clumps show relatively uniform temperatures and line widths throughout. Virial analysis suggests that the vast majority of clumps are gravitationally bound and are likely to be in a state of global free fall in the absence of strong magnetic fields. The similarities between the properties of the two subsamples suggest that the quiescent clumps are also likely to form massive stars in the future, and therefore provide a excellent opportunity to study the initial conditions of massive pre-stellar and protostellar clumps.

Accepted for publication by MNRAS. 25 pages, 21 figures and 6 tables. This paper also contains 100 pages of additional online images and tables that are not included here. A full resolution version of the paper including all of the online material can be found here http://rms.leeds.ac.uk/cgi-bin/public/RMS_PUBLICATIONS.cgi

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• ATLASGAL-selected massive clumps in the inner Galaxy: VI. Kinetic temperature and spatial density measured with formaldehyde
• H2O Southern Galactic Plane Survey (HOPS): Paper III - Properties of Dense Molecular Gas across the Inner Milky Way
• ALMA observations of NGC 6334S $-$ I: Forming massive stars and cluster in subsonic and transonic filamentary clouds
• Kinetic temperature of massive star forming molecular clumps measured with formaldehyde
• Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde. III. The Orion Molecular Cloud 1
• KFPA Examinations of Young STellar Object Natal Environments (KEYSTONE): Hierarchical Ammonia Structures in Galactic Giant Molecular Clouds
• ATLASGAL - Ammonia observations towards the southern Galactic Plane
• Thermal balance and comparison of gas and dust properties of dense clumps in the Hi-GAL survey
• Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde IV. The ALMA view of N113 and N159W in the LMC
• A Detailed View of the Circumstellar Environment and Disk of the Forming O-star AFGL 4176
• Interaction Between HII Region and AFGL333-Ridge: Implications to the Star Formation Scenario
• Ammonia observations towards the Aquila Rift cloud complex
• Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde V. The massive filament DR21
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• Spatial distribution of NH2D in massive star-forming regions
• Broad-velocity-width Molecular Features in the Galactic Plane
• Ammonia mapping observations of the Galactic infrared bubble N49: Three NH${}_3$ clumps along the molecular filament
• Search for High-Mass Protostellar Objects in Cold IRAS Sources
• KAgoshima Galactic Object survey with Nobeyama 45-metre telescope by Mapping in Ammonia lines (KAGONMA): Star formation feedback on dense molecular gas in the W33 complex