A Near-Infrared Imaging Survey of Coalsack Globule 2

Abstract

We describe a near-infrared imaging survey of Globule 2 in the Coalsack.This Bok globule is the highest-density region of this southern hemisphere molecular cloud and is the most likely location for young stars in this complex. The survey is complete for K<14.0, H<14.5, and J<15.5, several magnitudes more sensitive than previous observations of this globule. From the large number of background stars, we derive an accurate near-infrared extinction law for the cloud. Our result, EJ-H/EH-K=2.08+/-0.03, is significantly steeper than results for other southern clouds. We use the J-H/H-K color-color diagram to identify two potential young stars with K<14.0 in the region. We apply H-band star counts to derive the density profile of Coalsack Globule 2 and use a polytropic model to describe the internal structure of this small cloud. For a gas temperature T~15 K, this globule is moderately unstable.