New Analysis of Cold Clouds in Perseus Spiral Arm*

It is well known that stars form from the gravitational collapse of cold interstellar gas clouds within galaxies, but how such clouds themselves form remains up for debate. The origins and development of these clouds should therefore be investigated. Building on research by Sato (1990) and Hasegawa et al. (1983), we are investigating a section of the Perseus spiral arm. We are developing a new method of determining the abundance of cold hydrogen gas in this region, where passage through the arm may cause the clouds to evolve. Our approach compares cold atomic gas appearing as HI self-absorption (HISA), molecular gas traced by carbon monoxide (CO) emission, and thermal radiation from interstellar dust. We compare our results to Sato's and Hasegawa et al.'s to test and refine our analysis. Once our method is finalized, we will compare the gas properties (temperature, density, etc.) implied by different studies to assess how their analytic assumptions affect our knowledge of these clouds' evolutionary states and their prospects for future star formation.