2016ApJ...823L..17G -
Astrophys. J., 823, L17-L17 (2016/May-3)
Constraining gamma-ray emission from luminous infrared galaxies with Fermi-LAT: tentative detection of Arp 220.
GRIFFIN R.D., DAI X. and THOMPSON T.A.
Abstract (from CDS):
Star-forming galaxies produce gamma-rays primarily via pion production, resulting from inelastic collisions between cosmic-ray protons and the interstellar medium (ISM). The dense ISM and high star formation rates of luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs) imply that they should be strong gamma-ray emitters, but so far only two LIRGs have been detected. Theoretical models for their emission depend on the unknown fraction of cosmic-ray protons that escape these galaxies before interacting. We analyze Fermi-LAT data for 82 of the brightest Infrared Astronomical Satellite LIRGs and ULIRGs. We examine each system individually and carry out a stacking analysis to constrain their gamma-ray fluxes. We report the detection of the nearest ULIRG Arp 220 (∼4.6σ). We observe a gamma-ray flux (0.8-100 GeV) of 2.4 x 10–10 phot/cm2/s with a photon index of 2.23 (8.2 x 1041 erg/s at 77 Mpc). We also derive upper limits (ULs) for the stacked LIRGs and ULIRGs. The gamma-ray luminosity of Arp 220 and the stacked ULs agree with calorimetric predictions for dense star-forming galaxies. With the detection of Arp 220, we extend the gamma-ray-IR luminosity correlation to the high-luminosity regime with logL_{0.1-100GeV}=1.25×logL_{8-1000µm}+26.7 as well as the gamma-ray-radio continuum luminosity correlation with logL_{0.1-100GeV}=1.22×logL_{1.4GHz}+13.3 . The current survey of Fermi-LAT is on the verge of detecting more LIRGs/ULIRGs in the local universe, and we expect even more detections with deeper Fermi-LAT observations or the next generation of gamma-ray detectors.
Abstract Copyright:
© 2016. The American Astronomical Society. All rights reserved.
Journal keyword(s):
acceleration of particles - galaxies: individual: Arp 220 - galaxies: starburst - γ rays: galaxies
Simbad objects:
12
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