A Near-Infrared Imaging Survey of Coalsack Globule 2

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, E J - H / E H - 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.