The RMS survey: ammonia mapping of the environment of massive young stellar objects

Urquhart, J. S. and Figura, C. C. and Moore, T. J. T. and Csengeri, Tímea and Lumsden, S. L. (2015) The RMS survey: ammonia mapping of the environment of massive young stellar objects. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 452 (4). pp. 4029-4053. ISSN 0035-8711

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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′′ in 8′ regions towards the positions of embedded massive star formation. We have identified a total of 115 distinct clumps, approximately two-thirds of which are associ- ated with an embedded massive young stellar object or compact H ii region, while the others are classified as quiescent. There is a strong spatial correlation between the peak NH3 emis- sion and the presence of embedded objects. We derive the spatial distribution of the kinetic gas temperatures, line widths, and NH3 column densities from these maps, and by combin- ing these data with dust emission maps we estimate clump masses, H2 column densities and ammonia abundances. The clumps have typical masses of ∼1000 M⊙ and radii ∼0.5 pc, line widths of ∼2 km s−1 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 dis- tribution 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 ab- sence 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 there- fore provide a excellent opportunity to study the initial conditions of massive pre-stellar and protostellar clumps.

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