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

TL;DR

This study investigates the physical conditions of the infrared dark cloud G084.81-01.09 through molecular line observations, revealing early-stage massive star formation indicators such as dense ammonia cores and complex gas motions.

Contribution

It provides detailed physical characterization of an IRDC in early star formation stages using multi-molecular line data, highlighting initial conditions for massive star formation.

Findings

Six ammonia cores with masses 60-250 M_sun

Detection of self-reversed HCO+ profiles indicating complex motions

Evidence of early evolutionary stage of the cloud

Abstract

We mapped the MSX 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_sun, a kinetic temperature of 12 K, and a molecular 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 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.