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