X-ray sources in the starburst spiral galaxy M83: nuclear region and discrete source population

TL;DR

This study uses Chandra X-ray observations to analyze the nuclear region and discrete X-ray source population of the starburst galaxy M83, revealing detailed source distributions, spectral properties, and implications for star formation and supernova activity.

Contribution

It provides the first high-resolution X-ray analysis of M83's nuclear region, identifying source populations, spectral characteristics, and their relation to star formation and supernova enrichment.

Findings

81 X-ray point sources detected, 15 within the inner 16 arcsec

Unresolved emission mainly from hot plasma and faint sources

Different luminosity distributions for nuclear and outer sources

Abstract

Chandra has resolved the starburst nuclear region of the face-on grand-design spiral M83. Eighty-one point sources are detected above 3.5 sigma in the ACIS S3 image, and 15 of them are within the inner 16-arcsec region of the galaxy. A point source with L_x ~ 3 x 10^(38) erg/s in the 0.3--8.0 keV band is found to coincide with the infra-red nuclear photometric peak, one of the two dynamical nuclei of the galaxy. No point-like sources are resolved (at a 2.5-sigma level) at the centre of symmetry of the outer optical isophote ellipses, suspected to be another dynamical nucleus. About 50% of the total emission in the nuclear region is unresolved; of this, about 70% can be attributed to hot thermal plasma, and the rest is probably due to unresolved point sources (eg, faint X-ray binaries). The azimuthally-averaged radial distribution of the unresolved emission has a King-like profile, with no central cusp. Strong emission lines are seen in the spectrum of the optically thin plasma component. The high abundances of C, Ne, Mg, Si and S with respect to Fe suggest that the interstellar medium in the nucleus is enriched and heated by type-II supernova explosions and winds from massive stars. The cumulative luminosity distribution of the discrete X-ray sources is neither a single nor a broken power law. Separating the sources in the nuclear region (within a distance of 60 arcsec from the X-ray centre) from the rest reveals that the two groups have different luminosity distributions. The log[N(>S)]--log S curve of the sources in the inner region (nucleus and stellar bar) is a single power law, which we interpret as due to continuous, ongoing star formation. Outside the central region, there is a smaller fraction of sources brighter than the Eddington limit for an accreting neutron star.