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arXiv · 1603.06355

First detection of GeV emission from an ultraluminous infrared galaxy: Arp 220 as seen with the Fermi Large Area Telescope

Fang-Kun Peng·Xiang-Yu Wang·Ruo-Yu Liu·Qing-Wen Tang·Jun-Feng Wang
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Abstract

Cosmic rays (CRs) in starburst galaxies produce high energy gamma-rays by colliding with the dense interstellar medium (ISM). Arp 220 is the nearest ultra luminous infrared galaxy (ULIRG) that has star-formation at extreme levels, so it has long been predicted to emit high-energy gamma-rays. However, no evidence of gamma-ray emission was found despite intense efforts of search. Here we report the discovery of high-energy gamma-ray emission above 200 MeV from Arp 220 at a confidence level of $\sim 6.3 σ$ using 7.5 years of \textsl {Fermi} Large Area Telescope observations. The gamma-ray emission shows no significant variability over the observation period and it is consistent with the quasi-linear scaling relation between the gamma-ray luminosity and total infrared luminosity for star-forming galaxies, suggesting that these gamma-rays arise from CR interactions. As the high density medium of Arp 220 makes it an ideal CR calorimeter, the gamma-ray luminosity can be used to measure the efficiency of powering CRs by supernova (SN) remnants given a known supernova rate in Arp 220. We find that this efficiency is about $4.2\pm2.6\%$ for CRs above 1 GeV.

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Fang-Kun Peng, Xiang-Yu Wang, Ruo-Yu Liu, Qing-Wen Tang, Jun-Feng Wang. 2016-04-01. First detection of GeV emission from an ultraluminous infrared galaxy: Arp 220 as seen with the Fermi Large Area Telescope. https://doi.org/10.3847/2041-8205%2F821%2F2%2Fl20

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