BEXCO - Room C(108)
[GA257] Study of the Interstellar Medium and Cosmic Rays in the MBM 53-55 Clouds and the Pegasus Loop
- Tsunefumi MIZUNO
- Tsunefumi MIZUNO (Hiroshima University, Japan)
High-energy cosmic-ray (CR) protons and electrons interact with the interstellar gas or the interstellar radiation field and produce diffuse gamma rays. Since the interstellar medium (ISM) is transparent to these high-energy photons, GeV gamma rays are a powerful probe to study the ISM and Galactic CRs. In order to study the spatial and spectral distributions of CRs through gamma rays, either in the CR accelerators or in the interstellar space, the interstellar gas column densities need to be estimated with good accuracy using observations in other wavebands such as radio, infrared, and optical. Radio line observations at 21 cm and 2.6 mm have been used to trace the atomic and molecular gas distributions, respectively. Yet, a significant amount of gas not traced properly by these surveys was revealed by EGRET and has been confirmed by Fermi-LAT. In this contribution, we report the study of ISM and CRs in the nearby molecular clouds MBM 53, 54, and 55 and a far-infrared loop-like structure in Pegasus. By combining the dust thermal emission model based on Planck data with Fermi-LAT gamma-ray data, it was found that neither the dust radiance nor the dust opacity at 353 GHz was proportional to the total gas column density, but instead, their ratios to the gas column density depend on the dust temperature. Using the gamma-ray data as a robust gas tracer to compensate for the temperature dependence, we evaluated the total gas column densities by employing an empirical linear relation between the ratio of the total gas column density to radiance to the dust temperature. We will present details of the data analysis, results, and implications for the ISM and CRs.