Early phase of massive star formation: A case study of the infrared dark cloud G084.81-01.09

Abstract

We mapped the Mid-course Space Experiment dark cloud G084.81-01.09 in the NH3(1,1)-(4,4) lines and in the J = 1-0 transitions of 12CO, 13CO, C18O, and HCO+ in order to study the physical properties of infrared dark clouds, and to better understand the initial conditions for massive star formation. Six ammonia cores are identified with masses ranging from 60 to 250 M, a kinetic temperature of 12K, and a molecular hydrogen number density n(H2) 10 5cm-3. In our high-mass cores, the ammonia line width of 1kms-1 is larger than those found in lower mass cores but narrower than the more evolved massive ones. We detected self-reversed profiles in HCO+ across the northern part of our cloud and velocity gradients in different molecules. These indicate an expanding motion in the outer layer and more complex motions of the clumps more inside our cloud. We also discuss the millimeter wave continuum from the dust. These properties indicate that our cloud is a potential site of massive star formation but is still in a very early evolutionary stage. © 2011 The American Astronomical Society. All rights reserved.