Kavli Affiliate: Igor Moskalenko
| Summary:
To investigate the interstellar medium (ISM) and Galactic cosmic rays (CRs) in the solar neighborhood, we analyzed $γ$-ray data by Fermi Large Area Telescope (LAT) for five nearby molecular cloud regions. Our data includes the MBM/Pegasus region (MBM~53, 54, 55 clouds and Pegasus loop), R CrA region (R Coronae Australis clouds), Chamaeleon region (Chamaeleon clouds), Cep/Pol region (Cepheus and Polaris flare), and Orion region (Orion clouds). The ISM templates are constructed by a component decomposition of the 21~cm HI line, the Planck dust emission model, and the carbon monoxide (CO) 2.6~mm line. Through $γ$-ray data analysis the ISM gas is successfully decomposed into non-local HI, narrow-line and optically thick HI, broad-line and optically thin HI, CO-bright Htwo, and CO-dark Htwo for all five regions. CR intensities evaluated by the $γ$-ray emissivity of broad HI agree well with a model based on directly-measured CR spectra at the Earth, with a gradient giving a higher CR intensity toward the inner Galaxy at the 10% level in $sim$ 500~pc. The ratio of CO-dark Htwo to CO-bright Htwo anti-correlates with the Htwo mass traced by the CO 2.6~mm line, and reaches 5–10 for small systems of $sim$1000 solar mass.
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