Prospects of newly detecting nearby star-forming galaxies by the
  Cherenkov Telescope Array
  Prospects of the Cherenkov Telescope Array (CTA) for the study of very high
energy gamma-ray emission from nearby star-forming galaxies are investigated.
In the previous work, we constructed a model to calculate luminosity and energy
spectrum of pion-decay gamma-ray emission produced by cosmic-ray interaction
with the interstellar medium (ISM), from four physical quantities of galaxies
[star formation rate (SFR), gas mass, stellar mass, and effective radius]. The
model is in good agreement with the observed GeV--TeV emission of several
nearby galaxies. Applying this model to nearby galaxies that are not yet
detected in TeV (mainly from the KINGFISH catalog), their hadronic gamma-ray
luminosities and spectra are predicted. We identify galaxies of the highest
chance of detection by CTA, including NGC 5236, M33, NGC 6946, and IC 342.
Concerning gamma-ray spectra, NGC 1482 is particularly interesting because our
model predicts that this galaxy is close to the calorimetric limit and its
gamma-ray spectral index in GeV--TeV is close to that of cosmic-ray protons
injected into ISM. Therefore this galaxy may be detectable by CTA even though
its GeV flux is below the {\it Fermi} Large Area Telescope sensitivity limit.
In the TeV regime, most galaxies are not in the calorimetric limit, and the
predicted TeV flux is lower than that assuming a simple relation between the
TeV luminosity and SFR of M82 and NGC 253, typically by a factor of 15. This
means that a more sophisticated model beyond the calorimetric limit assumption
is necessary to study TeV emission from star-forming galaxies.
