Discovery of Young Stellar Objects at the Edge of the Optical Disk of Our Galaxy

Abstract

We report a discovery of young stellar objects associated with a molecular cloud at the edge of the optical disk of our Galaxy. This cloud is denoted as Cloud 2 in the list by Digel et al., and it is one of the most distant molecular clouds from the Galactic center known to date, with a probable distance of 15-19 kpc. We found seven red near-infrared (NIR) sources associated with this cloud. Based on our NIR observations and the far-infrared/radio data in the literature, we conclude that most sources are likely to be members of Cloud 2. The geometry of ionized gas, IRAS sources, NIR sources, and molecular cloud suggests that MR 1, an isolated early B-type star near Cloud 2, has triggered the star formation activity in Cloud 2. Our results show that ongoing star formation is present in Cloud 2 and that active star formation can occur in the farthest regions of the Galaxy, where the molecular gas density is extremely low, perturbation from the spiral arms is very small, and the metallicity is similar to that for irregular dwarf galaxies. Cloud 2 is an excellent laboratory in which to study the details of the star formation process in an environment that is similar to that in the early stage of the formation of the Galactic disk.