Discrete and diffuse X-ray emission in the nucleus and disk of the starburst spiral galaxy M83

Abstract

We have studied the face-on, barred spiral M83 (NGC 5236) with Chandra. Eighty-one point sources are detected (above 3.5-sigma) in the ACIS S3 image: 15 of them are within the inner 16 arcsec region (starburst nucleus, resolved for the first time with Chandra), and 23 within the inner 60 arcsec (including the bar). The luminosity distributions of the sources in the inner 60 arcsec region (nucleus and stellar bar) is a single power law, which we interpret as due to continuous, ongoing star formation. Outside this inner region, there is a smaller fraction of bright sources, which we interpret as evidence of an aging population from a past episode of star formation. About 50% of the total emission in the nuclear region is unresolved; of this, about 70% can be attributed to hot thermal plasma, and we interpret the rest as due to unresolved point sources (eg, faint X-ray binaries). The unresolved X-ray emission also shows differences between the nuclear region and the spiral arms. In the nuclear region, the electron temperature of the thermal plasma is = 0.58 keV. In the spiral arms, the thermal component is at kT = 0.31 keV and a power-law component dominates at energies >~1 keV. The high abundance of C, Ne, Mg, Si and S with respect to Fe suggests that the interstellar medium is enriched and heated by core-collapse supernova explosions and winds from massive stars.