National Aeronautics and Space Administration (NASA)
Location
Pasadena, CA | United States
Job description
Description
Star formation rates in galaxies depend on how much molecular H2 gas is present in dense cloud regions in which new stars form. Under most interstellar environments molecular H2 gas is not directly observed. CO line emission is used as proxy to trace the H2 gas in molecular clouds. However, there is a large uncertainty relating the observed CO line intensity to the underlying H2 column density. The presence of a significant fraction H2 molecular gas missed by CO as tracer, referred to as “CO-dark H2 gas“, has been inferred from a variety of probes including dust emission, gamma rays, and 158 micron CII fine structure line emission. (c.f. Velusamy et al. 2010, A&A 521, L18; Langer et al. 2010, A&A 521, L17). The dust continuum emission in IR, far-IR, and submm traces the high H2 molecular column densities. CII and CI fine structure lines trace the high H2 molecular column densities in the C+/C0/CO transition layers in molecular clouds which are missed by CO emission. The goal of this project is to investigate the distribution of the “CO-dark H2 gas“ across the Galaxy combining the CII, CI maps observed by Herschel HIFI (GOTC+ survey and follow up projects), with the dust emissions observed by Spitzer IRAC &MIPS, Herschel PACS & SPIRE, and submm maps by SCUBA & LABOCA. The results will be used to constraint the Xco factor (CO-H2 conversion factor defined the ratio of H2 column density to CO line intensity) which is widely used, but poorly constrained, and critical to our understanding of the star formation in galaxies and thus the galaxy evolution in the universe.
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