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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
radial distribution of the
unresolved emission has a Kinglike profile, with no cusp (Fig. 1).
0.2-10 keV luminosity (erg/s)
of the nuclear region (r < 16”)
DISCRETE SOURCES
UNRESOLVED SOURCES
optically thin thermal plasma
power-law component
TOTAL
9.3 x 1038
12.7 x 1038
9.2 x 1038
3.5 x 1038
1 kpc
22.0 x 1038
X-RAY EMISSION ALONG THE ARMS:
Ne X
Mg XI
Si XIII
C VI
S XV
O VIII
Ne IX
Fe XVII
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.
DISCRETE X-RAY SOURCE LUMINOSITY FUNCTION (LF):
A total of 81 point sources are detected in the ACIS-S3 chip at S/N > 3.5.
14 of them are in the nuclear region, previously unresolved. The offcentre 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,
theLF is steeper at the bright end (Fig. 3). The LF of the sources in the nuclear region is a simple power
slope and
of the
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.
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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:
X-ray contours (0.2-10 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 (southwest of the nucleus). Unresolved emission
extends along the direction of the bar and
perpendicular to it.
IR nucleus