DISCRETE SOURCES

1
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
0.2-10 keV luminosity (erg/s) of the nuclear
region (r lt 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).
X-RAY EMISSION ALONG THE ARMS Preliminary
analysis of the Chandra data shows that the
unresolved arm emission is due to hot gas at
T0.4 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 (0.2-10 keV flux) plotted over an
HST/WFPC2 image (V band). A bright (Lx3 x 1038
erg/s) source is found coincident with the
optical/IR nucleus. Its spectrum is an absorbed
power-law (G1.5), 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 gt 3.5. 14 of them are in the
nuclear region, previously unresolved. The
off-centre sources tend to associate with the
spiral arms. The cumulative log N(gtS) 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.
rs1_at_mssl.ucl.ac.uk