Title: Study of the Cosmic Rays and Interstellar Medium in Local H I Clouds Using Fermi-LAT Gamma-Ray Observations

Abstract

An accurate estimate of the interstellar gas density distribution is crucial to understanding the interstellar medium (ISM) and Galactic cosmic rays (CRs). To comprehend the ISM and CRs in a local environment, a study of the diffuse $$γ$$-ray emission in a midlatitude region of the third quadrant was performed. Specifically, the $$γ$$-ray data in the 0.1–25.6 GeV energy range of the Fermi Large Area Telescope (LAT) and other interstellar gas tracers such as the HI4PI survey data and the Planck dust thermal emission model were used, and the northern and southern regions were analyzed separately. The variation of the dust emission D_em with the total neutral gas column density N_H was studied in high dust temperature areas, and the N_H/D_em ratio was calibrated using $$γ$$-ray data under the assumption of a uniform CR intensity in the studied regions. The measured integrated $$γ$$-ray emissivities above 100 MeV are (1.58 ± 0.04) x 10^-26 photons s^-1 sr^-1H-atom-1 and (1.59 ± 0.02) x 10-26 photons s-1 sr-1 H-atom^-1 in the northern and southern regions, respectively, supporting the existence of a uniform CR intensity in the vicinity of the solar system. While most of the gas can be interpreted to be H I with a spin temperature of T_S = 125 K or higher, an area dominated by optically thick H I with T_S ~ 40 K was identified.

Authors:

Mizuno, T.  ^[1];

• Search DOE PAGES for author "Mizuno, T."
• Search DOE PAGES for ORCID "0000-0001-7263-0296"
• Search orcid.org for ORCID "0000-0001-7263-0296"

Abdollahi, S. ^[1]; Fukui, Y. ^[2]; Hayashi, K.  ^[2];

• Search DOE PAGES for author "Hayashi, K."
• Search DOE PAGES for ORCID "0000-0001-6922-6583"
• Search orcid.org for ORCID "0000-0001-6922-6583"

Koyama, T. ^[1]; Okumura, A.  ^[2];

• Search DOE PAGES for author "Okumura, A."
• Search DOE PAGES for ORCID "0000-0002-3055-7964"
• Search orcid.org for ORCID "0000-0002-3055-7964"

Tajima, H.  ^[3];

• Search DOE PAGES for author "Tajima, H."
• Search DOE PAGES for ORCID "0000-0002-1721-7252"
• Search orcid.org for ORCID "0000-0002-1721-7252"

Yamamoto, H. ^[2]

---

+ Show Author Affiliations

1. Hiroshima Univ. (Japan)
2. Nagoya Univ. (Japan)
3. Nagoya Univ. (Japan); SLAC National Accelerator Lab., Menlo Park, CA (United States)

Publication Date:

2020-02-19

Research Org.:

SLAC National Accelerator Lab., Menlo Park, CA (United States)

Sponsoring Org.:

National Aeronautics and Space Administration (NASA); USDOE; Commissariat à l’Energie Atomique; Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules (CNRS/IN2P3); Agenzia Spaziale Italiana; Istituto Nazionale di Fisica Nucleare (INFN); Agenzia Spaziale Italiana (ASI); Ministry of Education, Culture, Sports, Science and Technology (MEXT); High Energy Accelerator Research Organization (KEK); Japan Aerospace Exploration Agency (JAXA); K. A. Wallenberg Foundation; Swedish Research Council (VR); Swedish National Space Board (SNSB); Core of Research for the Energetic Universe at Hiroshima University

OSTI Identifier:

1617048

Grant/Contract Number:  

AC02-76SF00515; JP17H02866; JP26800160

Resource Type:

Accepted Manuscript

Journal Name:

The Astrophysical Journal (Online)

Additional Journal Information:

Journal Name: The Astrophysical Journal (Online); Journal Volume: 890; Journal Issue: 2; Journal ID: ISSN 1538-4357

Publisher:

Institute of Physics (IOP)

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; Galactic cosmic rays; Gamma-rays; Interstellar medium