Molecular Hydrogen Absorption Line Detected in Dense Molecular Clouds

Abstract

The H₂ ν=0–1 S(0) absorption line was detected together with CO ν=0–2 toward NGC 7538 IRS1 using IRCS at Subaru Telescope. The H2/CO ratio are directly measured to be 5100±1700 on the assumption that H₂ ortho-to-para ratio is 3. The H₂/CO ratio, which was measured in line of sight toward the Outer Galaxy, is ~1.4 times larger than ones measured in nearby YSOs (e.g., H₂/CO= 3700⁺³¹⁰⁰_–2600 toward NGC 2024 IRS2 by Lacy et al. 1994 [1]).