1. DISCRETE X-RAY SOURCE LUMINOSITY FUNCTION (LF):
DISCRETE SOURCES
AND DIFFUSE EMISSION IN M83
Roberto Soria & Kinwah Wu (MSSL/UCL)
M83 is a barred spiral galaxy with a starburst nucleus, located in the Centaurus A group, at a distance of 3.7 Mpc. It was observed by Chandra in 2000 April.
About 55% of the total emission in the nuclear region is unresolved. About 80% of the unresolved nuclear emission can be attributed to hot thermal plasma at T ~ 0.6 keV; the rest is mainly due to faint X-ray binaries. The azimuthally-averaged
keV luminosity (erg/s)
of the nuclear region (r < 16”)
DISCRETE SOURCES
9.3 x 1038
UNRESOLVED SOURCES
12.7 x 1038
optically thin thermal plasma
9.2 x 1038
power-law component
3.5 x 1038
TOTAL
22.0 x 1038
1 kpc
radial distribution of the unresolved emission has a King-like profile, with no cusp (Fig. 1).
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X-RAY EMISSION ALONG THE ARMS: Preliminary analysis of the Chandra data shows that the unresolved arm emission is due to hot gas at T~0.4 keV. We will use XMM to investigate possible temperature and metallicity gradients along the arms.
NUCLEAR REGION:
Strong emission lines are found in the spectrum of the unresolved nuclear emission (Fig. 2). The high abundances of Ne, Mg, Si and S suggest that the ISM is heated and enriched by frequent Type-II SN explosions.
Ne X
C VI
Mg XI
Si XIII
S XV
Ne IX
X-ray contours ( keV flux) plotted over an HST/WFPC2 image (V band). A bright (Lx~3 x 1038 erg/s) source is found coincident with the optical/IR nucleus. Its spectrum is an absorbed power-law (G=1.5), consistent with accretion onto a massive BH. Other discrete sources are found along the star-forming arc (south-west of the nucleus). Unresolved emission extends along the direction of the bar and perpendicular to it.
O VIII
Fe XVII
DISCRETE X-RAY SOURCE LUMINOSITY FUNCTION (LF):
A total of 81 point sources are detected in the ACIS-S3 chip at S/N > of them are in the nuclear region, previously unresolved. The off-centre sources tend to associate with the spiral arms. The cumulative log N(>S) – log S distribution is different for the source populations in the nuclear region and in the disk (outside 60”, ~ 1 kpc). For the disk sources, there is a kink at the Eddington luminosity of accreting neutron stars, and the
IR nucleus
slope of the LF is steeper at the bright end (Fig. 3). The LF of the sources in the nuclear region is a simple power law instead. This indicates that the population of sources in the inner region has a larger relative fraction of bright sources than the disk population, in contrast to M81, where most bright sources are in the disk. If a single power-law LF is a consequence of active star formation (Wu 2001), this difference is due to the fact that M83 has an active starburst nucleus, while star formation in M81 is more efficient in the disk.