We present the results of a GBT survey of NH _ { 3 } ( 1,1 ) , ( 2,2 ) , ( 3,3 ) lines towards 631 Bolocam Galactic Plane Survey ( BGPS ) sources at a range of Galactic longitudes in the inner Galaxy .
We have detected the NH _ { 3 } ( 1,1 ) line towards 72 % of our targets ( 456 ) , demonstrating that the high column density features identified in the BGPS and other continuum surveys accurately predict the presence of dense gas .
We have determined kinematic distances and resolved the distance ambiguity for all BGPS sources detected in NH _ { 3 } .
The BGPS sources trace the locations of the Scutum and Sagittarius spiral arms , with the number of sources peaking between R _ { Gal } \sim 4 - 5 kpc .
We measure the physical properties of each source and find that depending on the distance , BGPS sources are primarily clumps , with some cores and clouds .
We have examined the physical properties as a function of Galactocentric distance , and find a mean gas kinetic temperature of 15.6 K , and that the NH _ { 3 } column density and abundance decrease by nearly an order of magnitude between \mbox { $R _ { Gal } $ } \sim 3 - 11 kpc .
Comparing sources at similar distances demonstrates that the physical properties are indistinguishable , which suggests a similarity in clump structure across the Galactic disk .
We have also compared the BGPS sources to criteria for efficient star formation presented independently by Heiderman et al .
and Lada et al. , and massive star formation presented by Kauffmann et al .
48 % of our sample should be forming stars ( including massive stars ) with high efficiency , and 87 % contain subregions that should be efficiently forming stars .
Indeed , we find that 67 % of the sample exhibit signs of star formation activity based on an association with a mid-IR source .