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

Abstract

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 ($L_{\gamma }$) of star-forming galaxies is well correlated with their star formation rates (SFR). We investigated \textsl{Fermi} data of eight Galactic molecular clouds in the Gould belt and found that molecular clouds do not follow the $L_{\gamma }-\mathrm{SFR}$ 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 {\em \textup{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 {\em \textup{active}} sources.

Accepted for publication in Astronomy & Astrophysics

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Cited by in corpus (5)

• The gamma-ray / infrared luminosity correlation of star-forming galaxies
• Evidence of AGN activity in the gamma-ray emission from two starburst galaxies
• The extragalactic $\gamma$-ray background: imprints from the physical properties and evolution of star-forming galaxy populations
• Interpreting the relation between the gamma-ray and infrared luminosities of star-forming galaxies
• Probing local cosmic rays using Fermi-LAT observation of a mid-latitude region in the third Galactic quadrant