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We mapped the MSX dark cloud G084.81-01.09 in the NH3 (1,1) - (4,4) lines andin the J = 1-0 transitions of 12CO, 13CO, C18O and HCO+ in order to study thephysical properties of infrared dark clouds, and to better understand theinitial conditions for massive star formation. Six ammonia cores are identifiedwith masses ranging from 60 to 250 M_sun, a kinetic temperature of 12 K, and amolecular hydrogen number density n(H2) ~ 10^5 cm^-3. In our high mass cores,the ammonia line width of 1 km/s is larger than those found in lower mass coresbut narrower than the more evolved massive ones. We detected self-reversedprofiles in HCO+ across the northern part of our cloud and velocity gradientsin different molecules. These indicate an expanding motion in the outer layerand more complex motions of the clumps more inside our cloud. We also discussthe millimeter wave continuum from the dust. These properties indicate that ourcloud is a potential site of massive star formation but is still in a veryearly evolutionary stage.

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