Discovery of GeV emission from the direction of the luminous infrared galaxy NGC 2146

TL;DR

This paper reports the detection of GeV gamma-ray emission from the luminous infrared galaxy NGC 2146, indicating it acts as a proton calorimeter and supports the link between star formation and gamma-ray emission.

Contribution

First detection of GeV gamma-ray emission from NGC 2146, demonstrating its role as a proton calorimeter and confirming the gamma-ray and infrared luminosity correlation in star-forming galaxies.

Findings

Detected gamma-ray emission from NGC 2146 at ~5.5 sigma significance.

NGC 2146 follows the gamma-ray and infrared luminosity scaling relation.

NGC 2146 likely converts most cosmic ray energy into secondary pions.

Abstract

Recent detection of high-energy gamma-ray emission from starburst galaxies M82 and NGC 253 suggests that starburst galaxies are huge reservoirs of cosmic rays and these cosmic rays convert a significant fraction of their energy into gamma-rays by colliding with the dense interstellar medium. In this paper, we report the search for high-energy gamma-ray emission from several nearby star-forming and starburst galaxies using the 68 month data obtained with the Fermi Large Area Telescope. We found a $\sim5.5\sigma$ detection of gamma-ray emission above 200{\rm MeV} from a source spatially coincident with the location of the luminous infrared galaxy NGC~2146. Taking into account also the temporal and spectral properties of the gamma-ray emission, we suggest that the gamma-ray source is likely to be the counterpart of NGC~2146. The gamma-ray luminosity suggests that cosmic rays in NGC~2146 convert most of their energy into secondary pions, so NGC~2146 is a "proton calorimeter". It is also found that NGC~2146 obeys the quasi-linear scaling relation between the gamma-ray luminosity and total infrared luminosity for star-forming galaxies, strengthening the connection between massive star formation and gamma-ray emission of star-forming galaxies. Possible TeV emission from NGC~2146 is predicted and the implications for high-energy neutrino emission from starburst galaxies are discussed.