EARLY PHASE OF MASSIVE STAR FORMATION: A CASE STUDY OF THE INFRARED DARK CLOUD G084.81-01.09

We mapped the Mid-course Space Experiment dark cloud G084.81-01.09 in the NH(3)(1,1)-(4,4) lines and in the J = 1-0 transitions of (12)CO, (13)CO, C(18)O, 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(circle dot), a kinetic temperature of 12 K, and a molecular hydrogen number density n(H(2)) similar to 10(5) cm(-3). In our high-mass cores, the ammonia line width of 1 km s(-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.