Constraining gamma-ray emission from luminous infrared galaxies with Fermi-LAT; tentative detection of ARP 220
- Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019 (United States)
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 × 10{sup −10} phot cm{sup −2} s{sup −1} with a photon index of 2.23 (8.2 × 10{sup 41} erg s{sup −1} 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{sub 0.1−100GeV}=1.25×logL{sub 8−1000μm}+26.7 as well as the gamma-ray–radio continuum luminosity correlation with logL{sub 0.1−100GeV}=1.22×logL{sub 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.
- OSTI ID:
- 22869067
- Journal Information:
- Astrophysical Journal Letters, Vol. 823, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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