Kavli Affiliate: Igor V. Moskalenko
| First 5 Authors: Tsunefumi Mizuno, Katsuhiro Hayashi, Hinako Ochi, Igor V. Moskalenko, Elena Orlando
| Summary:
To investigate the interstellar medium (ISM) and Galactic cosmic rays (CRs)
in the solar neighborhood, we analyzed ${gamma}$-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 $gamma$-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 ${gamma}$-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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