Probing the diffuse and translucent clouds with absorption lines
Seminar by Gan Luo (Grenoble), 12 February 2024, 16h CET (15h UT)
Molecular gas is the raw material for forming stars. However, the process by which diffuse molecular gas transforms into dense cores is not fully understood. With the increasing capabilities of millimeter telescopes such as ALMA and NOEMA, we are able to probe diffuse and translucent molecular clouds with unprecedented sensitivity. In this talk, I will introduce our recent progress with molecular absorption lines against quasars. Our observations reveal the ubiquitous CO-dark molecular gas in the solar neighborhood, highlighting a consistent molecular formation threshold for clouds in both the solar neighborhood and low-metallicity outer disk region. Notably, we have detected DCN in low-density gas for the first time. The over-budget deuteration fraction, exceeding predictions from current chemical models, suggests a possible enhancement in low-density gas. By combining our observations with chemical models, we have successfully demonstrated the feasibility of using O-bearing molecules to infer the cosmic-ray ionization rate. Our findings coincide with the cosmic-ray attenuation models, offering a plausible explanation for the discrepancy in the cosmic-ray ionization rate between measurements obtained from Voyager and ions.
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Topic: Monthly joint seminar
Time: Feb 12, 2024 16:00 Paris
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