A multi-wavelength study of Supernova Remnants in six nearby galaxies.
  I: Detection of new X-ray selected Supernova Remnants with Chandra
  We present results from a study of the Supernova Remnant (SNR) population in
a sample of six nearby galaxies (NGC 2403, NGC 3077, NGC 4214, NGC 4449, NGC
4395 and NGC 5204) based on Chandra archival data. We have detected 244
discrete X-ray sources down to a limiting flux of 10^{-15} erg/s. We identify
37 X-ray selected thermal SNRs based on their X-ray colors or spectra, 30 of
which are new discoveries. In many cases the X-ray classification is confirmed
based on counterparts with SNRs identified in other wavelengths. Three of the
galaxies in our sample (NGC 4214, NGC 4395 and NGC 5204) are studied for the
first time, resulting in the discovery of 13 thermal SNRs. We discuss the
properties (luminosity, temperature, density) of the X-ray detected SNRs in the
galaxies of our sample in order to address their dependence on their
environment. We find that X-ray selected SNRs in irregular galaxies appear to
be more luminous than those in spirals. We attribute this to the lower
metalicities and therefore more massive progenitor stars of irregular galaxies
or the higher local densities of the ISM. We also discuss the X-ray selected
SNR populations in the context of the Star Formation Rate of their host
galaxies. A comparison of the numbers of observed luminous X-ray selected SNRs
with those expected based on the luminosity functions of X-ray SNRs in the MCs
and M33 suggest different luminosity distributions between the SNRs in spiral
and irregular galaxies with the latter tending to have flatter distributions.
