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キーワード:
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要旨:
All galaxies without a radio-loud AGN follow a tight correlation between their global FIR and
radio synchrotron luminosities, which is believed to be ultimately the result of the formation of
massive stars. Two face-on colliding pairs of galaxies, UGC12914/5 and UGC 813/6 deviate from
this correlation and show an excess of radio emission which in both cases originates to a large
extent in a gas bridge connecting the two galactic disks. The radio synchrotron emission expected
from the bridge region is calculated, assuming that the kinetic energy liberated in the predominantly
gas dynamic interaction of the respective interstellar media (ISM) has produced shock
waves that efficiently accelerate nuclei and electrons to relativistic energies. A simple model for
the acceleration of relativistic particles in these shocks is presented together with a calculation of
the resulting radio emission, its spectral index and the expected high-energy gamma-ray emission.
This process is not related to star formation. It is found that the nonthermal energy produced in
the collision is large enough to explain the radio emission from the bridge between the two galaxies.
The calculated spectral index at the present time also agrees with the observed value. The
expected gamma-ray emission, on the other hand, is too low by a factor of several to be detectable
even with foreseeable instruments like CTA.
