Quantifying the interstellar medium and cosmic rays in the MBM 53, 54, and 55 molecular clouds and the pegasus loop using Fermi-LAT gamma-ray observations
- Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan)
- Department of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan)
- Department of Physics and Astrophysics, Nagoya University, Nagoya, Aichi 464-8602 (Japan)
A study of the interstellar medium (ISM) and cosmic rays (CRs) using Fermi Large Area Telescope (LAT) data, in a region encompassing the nearby molecular clouds MBM 53, 54, and 55 and a far-infrared loop-like structure in Pegasus, is reported. By comparing the Planck dust thermal emission model with Fermi-LAT γ-ray data, it was found that neither the dust radiance (R) nor the dust opacity at 353 GHz (τ {sub 353}) was proportional to the total gas column density N(H{sub tot}) primarily because N(H{sub tot})/R and N(H{sub tot})/τ {sub 353} depend on the dust temperature (T {sub d}). The N(H{sub tot}) distribution was evaluated using γ-ray data by assuming the regions of high T {sub d} to be dominated by optically thin atomic hydrogen (H I) and by employing an empirical linear relation of N(H{sub tot})/R to T {sub d}. It was determined that the mass of the gas not traced by the 21 cm or 2.6 mm surveys is ∼25% of the mass of H I in the optically thin case and is larger than the mass of the molecular gas traced by carbon monoxide by a factor of up to 5. The measured γ-ray emissivity spectrum is consistent with a model based on CR spectra measured at the Earth and a nuclear enhancement factor of ≤1.5. It is, however, lower than local H I emissivities reported by previous Fermi-LAT studies employing different analysis methods and assumptions on ISM properties by 15%–20% in energies below a few GeV, even if we take account of the statistical and systematic uncertainties. The origin of the discrepancy is also discussed.
- OSTI ID:
- 22869630
- Journal Information:
- Astrophysical Journal, Vol. 833, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Gas and Dust Properties in the Chamaeleon Molecular Cloud Complex Based on the Optically Thick H i
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journal | June 2019 |
Fermi -LAT γ -Ray Study of the Interstellar Medium and Cosmic Rays in the Chamaeleon Molecular Cloud Complex: A Look at the Dark Gas as Optically Thick H i
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journal | October 2019 |
Deciphering Residual Emissions: Time-dependent Models for the Nonthermal Interstellar Radiation from the Milky Way
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journal | December 2019 |
| Gas and Dust Properties in the Chamaeleon Molecular Cloud Complex based on the Optically Thick HI | text | January 2019 |
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