A Chain of Dark Clouds in Projection Against the Galactic Center

Abstract

In a |$J$|⁠, |$H$|⁠, and |$K_{\rm S}$| band survey of the Galactic center region over an area of 2|${}^\circ$||$\times$| 5|${}^\circ$|⁠, we have found many dark clouds, among which a distinguished chain of dark clouds can be identified with a quiescent CO cloud. The distances of the clouds are estimated to be 3.2–4.2 kpc, corresponding to the Norma arm, by our new method for determining the distances to dark clouds using the cumulative number of stars against the |$J-K_{\rm S}$| color. By adopting these estimated distances, the size and total mass of the cloud are estimated to be |$\sim$|70 pc in length and 6 |$\times$| 10|$^4$||$M_\odot$|⁠, respectively. Three compact HII regions exist in the cloud, indicating that star-forming activities are going on at the cores of the quiescent CO cloud on the spiral arm.