http://arxiv.org/abs/2003.07830
Star-forming galaxies are huge reservoirs of cosmic rays (CRs) and these CRs convert a significant fraction of their energy into gamma-rays by colliding with the interstellar medium (ISM). Several nearby star-forming galaxies have been detected in GeV-TeV $\gamma$-rays. It is also found that the $\gamma$-ray luminosities in 0.1-100 GeV correlate well with indicators of star formation rates of the galaxies, such as the total infrared (IR) luminosity. In this paper, we report a systematic search for possible gamma-ray emission from galaxies in the IRAS Revised Bright Galaxies Sample, using 11.4 years of $\gamma$-ray data taken by the Fermi-LAT. Two new galaxies, M33 and Arp 299, are detected with significance of ${\rm TS}\geq 25$. The two galaxies are consistent with the empirical correlation between the $\gamma$-ray luminosity and total infrared luminosity, suggesting that their gamma-ray emissions should mainly originate from CRs interacting with ISM. Nevertheless, there is a tentative evidence that the flux of the gamma-ray emission from Arp 299 is variable. If the variability is true, part of the emission should originate from the obscured AGN in this interacting galaxy system. In addition, we find the gamma-ray excess in M33 locates at the northeast region of the galaxy, where a supergiant H II region, NGC 604, resides. This indicates that some bright star-forming regions in spiral galaxies could outshine the bulk of the galaxy disk in producing gamma-ray emission.
S. Xi, R. Liu, H. Zhang, et. al.
Wed, 18 Mar 20
46/46
Comments: 8 pages, 9 figures, 2 tables; Comments are welcome
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