Comparative study of gamma-ray emission from molecular clouds and star-forming galaxies

Star-forming regions on different scales, such as giant molecular clouds in our Galaxy and star-forming galaxies, emit GeV gamma-rays. These are thought to originate from hadronic interactions of cosmic-ray (CR) nuclei with the interstellar medium. It has recently been shown that the gamma-ray lumin...

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Bibliographic Details
Published in:Astronomy and astrophysics (Berlin) 2019-01, Vol.621, p.A70
Main Authors: Peng, Fang-Kun, Xi, Shao-Qiang, Wang, Xiang-Yu, Zhi, Qi-Jun, Li, Di
Format: Article
Language:English
Subjects:
Clouds
Comparative studies
Cosmic rays
Dependence
Emission analysis
Galaxies
Gamma rays
gamma rays: ISM
Interstellar matter
ISM: clouds
Luminosity
methods: statistical
Milky Way
Molecular clouds
Regression analysis
Satellites
Star & galaxy formation
Star formation
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Summary:Star-forming regions on different scales, such as giant molecular clouds in our Galaxy and star-forming galaxies, emit GeV gamma-rays. These are thought to originate from hadronic interactions of cosmic-ray (CR) nuclei with the interstellar medium. It has recently been shown that the gamma-ray luminosity (Lγ) of star-forming galaxies is well correlated with their star formation rates (SFR). We investigated Fermi data of eight Galactic molecular clouds in the Gould belt and found that molecular clouds do not follow the Lγ −SFR correlation of star-forming galaxies. We also compared the scaling relations of gamma-ray luminosity, SFR, and the gas mass for molecular clouds and star-forming galaxies. Using a multiple-variable regression analysis, we found different dependences of gamma-ray emission on SFR or mass for molecular clouds and star-forming galaxies. This suggests that different mechanisms may govern the production of gamma-rays in these two types of sources. Specifically, the strong dependence on mass supports that gamma-ray emission of molecular clouds primarily comes from passive interaction by diffuse Galactic CRs, whereas the strong dependence on SFR supports that gamma-ray emission of star-forming galaxies originates from CRs that are accelerated by local active sources.
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361/201833859