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Title: 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

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 farinfrared loop-like structure in Pegasus, is reported. By comparing 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 (τ353) were proportional to the total gas column density N(Htot) primarily because N(Htot)/R and N(Htot)/τ353 depend on the dust temperature (Td). The N(Htot) distribution was evaluated using γ-ray data by assuming the regions of high Td to be dominated by optically thin atomic hydrogen (HI) and by employing an empirical linear relation of N(Htot)/R to Td. 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 HI 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 the nuclear enhancement factor of ≤1.5. Itmore » is, however, lower than local HI 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.« less
Authors:
ORCiD logo [1] ;  [1] ;  [2] ;  [2] ;  [2] ; ORCiD logo [3] ;  [2]
  1. Hiroshima Univ. (Japan)
  2. Nagoya Univ. (Japan)
  3. Nagoya Univ. (Japan); SLAC National Accelerator Lab., Menlo Park, CA (United States)
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 833; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS
OSTI Identifier:
1354846

Mizuno, T., Abdollahi, S., Fukui, Y., Hayashi, K., Okumura, A., Tajima, H., and Yamamoto, H.. 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. United States: N. p., Web. doi:10.3847/1538-4357/833/2/278.
Mizuno, T., Abdollahi, S., Fukui, Y., Hayashi, K., Okumura, A., Tajima, H., & Yamamoto, H.. 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. United States. doi:10.3847/1538-4357/833/2/278.
Mizuno, T., Abdollahi, S., Fukui, Y., Hayashi, K., Okumura, A., Tajima, H., and Yamamoto, H.. 2016. "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". United States. doi:10.3847/1538-4357/833/2/278. https://www.osti.gov/servlets/purl/1354846.
@article{osti_1354846,
title = {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},
author = {Mizuno, T. and Abdollahi, S. and Fukui, Y. and Hayashi, K. and Okumura, A. and Tajima, H. and Yamamoto, H.},
abstractNote = {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 farinfrared loop-like structure in Pegasus, is reported. By comparing 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 (τ353) were proportional to the total gas column density N(Htot) primarily because N(Htot)/R and N(Htot)/τ353 depend on the dust temperature (Td). The N(Htot) distribution was evaluated using γ-ray data by assuming the regions of high Td to be dominated by optically thin atomic hydrogen (HI) and by employing an empirical linear relation of N(Htot)/R to Td. 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 HI 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 the nuclear enhancement factor of ≤1.5. It is, however, lower than local HI 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.},
doi = {10.3847/1538-4357/833/2/278},
journal = {The Astrophysical Journal (Online)},
number = 2,
volume = 833,
place = {United States},
year = {2016},
month = {12}
}