THE FIRST DETECTION OF GeV EMISSION FROM AN ULTRALUMINOUS INFRARED GALAXY: Arp 220 AS SEEN WITH THE FERMI LARGE AREA TELESCOPE

ABSTRACT Cosmic rays (CRs) in starburst galaxies produce high-energy gamma-rays by colliding with the dense interstellar medium. Arp 220 is the nearest ultraluminous infrared galaxy that has star formation at extreme levels, so it has long been predicted to emit high-energy gamma-rays. However, no e...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2016-04, Vol.821 (2), p.L20-L20
Main Authors: Peng, Fang-Kun, Wang, Xiang-Yu, Liu, Ruo-Yu, Tang, Qing-Wen, Wang, Jun-Feng
Format: Article
Language:English
Subjects:
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Confidence intervals
COSMIC GAMMA SOURCES
cosmic rays
DENSITY
DETECTION
EFFICIENCY
Emission
GALAXIES
galaxies: starburst
GAMMA RADIATION
Gamma rays
gamma rays: galaxies
GEV RANGE
Infrared
INTERSTELLAR SPACE
LUMINOSITY
MEV RANGE
PHOTON EMISSION
STAR EVOLUTION
STARS
SUPERNOVA REMNANTS
Supernovae
TELESCOPES
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Summary:ABSTRACT Cosmic rays (CRs) in starburst galaxies produce high-energy gamma-rays by colliding with the dense interstellar medium. Arp 220 is the nearest ultraluminous infrared galaxy 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 search efforts. Here we report the discovery of high-energy gamma-ray emission above 200 MeV from Arp 220 at a confidence level of ∼6.3 using 7.5 years of 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 2.6% for CRs above 1 GeV.
ISSN:2041-8205
2041-8213
DOI:10.3847/2041-8205/821/2/L20