THE BOLOCAM GALACTIC PLANE SURVEY. VII. CHARACTERIZING THE PROPERTIES OF MASSIVE STAR-FORMING REGIONS

Abstract

We present the results of a GBT survey of NH3(1,1), (2,2), (3,3) lines\ntowards 631 Bolocam Galactic Plane Survey (BGPS) sources at a range of Galactic\nlongitudes in the inner Galaxy. We have detected the NH3(1,1) line towards 72%\nof our targets (456), demonstrating that the high column density features\nidentified in the BGPS and other continuum surveys accurately predict the\npresence of dense gas. We have determined kinematic distances and resolved the\ndistance ambiguity for all BGPS sources detected in NH3. The BGPS sources trace\nthe locations of the Scutum and Sagittarius spiral arms, with the number of\nsources peaking between Galactocentric radii of 4-5 kpc. We measure the\nphysical properties of each source and find that depending on the distance,\nBGPS sources are primarily clumps, with some cores and clouds. We have examined\nthe physical properties as a function of Galactocentric distance, and find a\nmean gas kinetic temperature of 15.6 K, and that the NH3 column density and\nabundance decrease by nearly an order of magnitude between Galactocentric radii\nof 3 - 11 kpc. Comparing sources at similar distances demonstrates that the\nphysical properties are indistinguishable, which suggests a similarity in clump\nstructure across the Galactic disk. We have also compared the BGPS sources to\ncriteria for efficient star formation presented independently by Heiderman et\nal. and Lada et al., and massive star formation presented by Kauffmann et al.\n48% of our sample should be forming stars (including massive stars) with high\nefficiency, and 87% contain subregions that should be efficiently forming\nstars. Indeed, we find that 67% of the sample exhibit signs of star formation\nactivity based on an association with a mid-IR source.\n