Massimo Persic, Yoel Rephaeli
The energy density of cosmic-ray protons (CRp) in star-forming galaxies can
be estimated from (i) neutral-pion--decay gamma-ray emission, (ii) synchrotron
radio emission, and (iii) supernova rates. For most of the galaxies for which
values of all these quantities are known, the three methods yield consistent
CRp energy density estimates, ranging from O(0.1) eV/cm3 in galaxies with low
star-formation rates, to O(100) eV/cm3 in galaxies with high star-formation
rates. The only cases for which the methods do not agree are the composite
starburst/Seyfert2 galaxy NGC1068, whose gamma-ray emission originates in
black-hole accretion rather than star formation, and the Small Magellanic
Cloud, where the discrepancy between measured and estimated CRp energy density
may be due to a small CR confinement volume.
View original:
http://arxiv.org/abs/1201.0369
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