Gamma-Ray Emission from Arp 220: Indications of an Active Galactic Nucleus

Abstract

Extragalactic cosmic ray populations are important diagnostic tools for tracking the distribution of energy in nuclei and for distinguishing between activity powered by star formation versus active galactic nuclei (AGNs). Here, we compare different diagnostics of the cosmic ray populations of the nuclei of Arp 220 based on radio synchrotron observations and the recent gamma-ray detection. We find the gamma-ray and radio emission to be incompatible; a joint solution requires at minimum a factor of 4 - 8 times more energy coming from supernovae and a factor of 40 - 70 more mass in molecular gas than is observed. We conclude that this excess of gamma-ray flux in comparison to all other diagnostics of star-forming activity indicates that there is an AGN present that is providing the extra cosmic rays, likely in the western nucleus.

5 pages, 3 figures, 1 table, accepted for publication in MNRAS Letters

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Cited by in corpus (26)

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• Contribution of starburst nuclei to the diffuse gamma-ray and neutrino flux
• MUSE view of Arp220: Kpc-scale multi-phase outflow and evidence for positive feedback
• Are Starburst Galaxies Proton Calorimeters?
• Resolved Structure of Arp 220 Nuclei at λ~3 mm
• High-energy gamma-ray and neutrino production in star-forming galaxies across cosmic time: Difficulties in explaining the IceCube data
• Could nearby star-forming galaxies light up the point-like neutrino sky?
• Local AGN Survey (LASr): I. Galaxy sample, infrared colour selection and predictions for AGN within 100 Mpc
• Exploring the physics behind the non-thermal emission from star-forming galaxies detected in gamma rays
• Evidence of AGN activity in the gamma-ray emission from two starburst galaxies
• Inverse Compton Signatures of Gamma-Ray Burst Afterglows
• Starburst and post-starburst high-redshift protogalaxies: The feedback impact of high energy cosmic rays
• IceCube Neutrinos from Hadronically Powered Gamma-Ray Galaxies
• Characterising the signatures of star-forming galaxies in the extra-galactic $\gamma$-ray background
• No evidence of AGN features in the nuclei of Arp 220 from JWST/NIRSpec IFS
• Breaking the Radio - Gamma-Ray Connection in Arp 220
• Arp 220: New Observational Insights into the Structure and Kinematics of the Nuclear Molecular Disks and Surrounding Gas
• Observable Signatures of Cosmic Rays Transport in Starburst Galaxies on Gamma-ray and Neutrino Observations
• Arp 220: A Post-Starburst Galaxy With Little Star Formation Outside of It's Nuclear Disks
• Secondary Radio and X-ray Emissions from Galaxy Mergers
• Spatially-resolved relation between [CI] ${}^3{P}_1$-${}^3{P}_0$ and ${}^{12}$CO (1-0) in Arp 220
• Prospects of newly detecting nearby star-forming galaxies by the Cherenkov Telescope Array
• CONGRuENTS (COsmic-ray, Neutrino, Gamma-ray and Radio Non-Thermal Spectra). I. A predictive model for galactic non-thermal emission