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 (NH 3 ) (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 associated 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 NH 3 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 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 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.

ATLASGAL-selected massive clumps in the inner Galaxy

“…(Wang et al 2009), but is lower than that found with NH 3 (Wouterloot et al 1988;Myers et al 1991;Jijina et al 1999;Wu et al 2006;Urquhart et al 2011Urquhart et al , 2015. The correlation appears consistent with the idea that the internal velocity dispersion of the dense clumps can be used to determine the mass of the formed stars (Saito et al 2001).…”

“…Previous observations of NH 3 (Wouterloot et al 1988;Myers et al 1991;Harju et al 1993;Ladd et al 1994;Molinari et al 1996;Jijina et al 1999;Wu et al 2006;Urquhart et al 2011Urquhart et al , 2015, C 18 O (Saito et al 2001;Ridge et al 2003;Maud et al 2015), and 13 CO (Wang et al 2009;Lundquist et al 2015) suggest that the line width is correlated with luminosity, which indicates the presence of a link between formed stars and velocity dispersion. We investigate the line width-luminosity relation in the case of the dense gas tracer H 2 CO. We plot the line width-luminosity relation in Figure 9.…”

“…Wouterloot et al 1988;Molinari et al 1996;Jijina et al 1999;Wu et al 2006;Urquhart et al 2011Urquhart et al , 2015Wienen et al 2012;Lu et al 2014;Immer et al 2016;Tang et al 2017c) suggest that the line width is correlated with kinetic temperature. It is suggested that the correlation between kinetic temperature and line width is due to a conversion of turbulent energy into heat in the Galactic central clouds (e.g.…”

“…The straight lines are results from unweighed linear fits. Urquhart et al 2011Urquhart et al , 2015Wienen et al 2012;Lu et al 2014;Tang et al 2017c). The gas is heated by turbulent energy according to the approximate relation T kin ∝ ∆v 0.8−1.0 (gas kinetic temperature measured with NH 3 and H 2 CO) in molecular clouds of the Galactic centre (Güsten et al 1985;Mauersberger et al 1987;Immer et al 2016), which is consistent with our result (only in terms of slope, not of intercept and absolute value).…”

H2O Southern Galactic Plane Survey (HOPS): Paper III – properties of dense molecular gas across the inner Milky Way

“…Pillai et al 2006;Longmore et al 2007;Hill et al 2010;Ragan, Bergin & Wilner 2011;Dunham et al 2011;Urquhart et al 2011;Wienen et al 2012;Urquhart et al 2015).…”