2025/06/19 by Mizuno, Tsunefumi, Hayashi, Katsuhiro, Ochi, Hinako +3
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #Solar and Space Plasma Dynamics
paper · pdf · doi:10.48550/arxiv.2506.16252
openalex publication_date 2025/06/19 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
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 ∼ 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 ∼1000 solar mass.