  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.
