A MULTIWAVELENGTH STUDY OF SUPERNOVA REMNANTS IN SIX NEARBY GALAXIES. I. DETECTION OF NEW X-RAY-SELECTED SUPERNOVA REMNANTS WITH CHANDRA

摘要

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–1 cm–2. 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, and 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 metallicities and therefore more massive progenitor stars of irregular galaxies or the higher local densities of the interstellar medium. 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 Magellanic Clouds and M33 suggest different luminosity distributions between the SNRs in spiral and irregular galaxies with the latter tending to have flatter distributions.