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2003ApJS..144..213S - Astrophys. J., Suppl. Ser., 144, 213-242 (2003/February-0)
Chandra X-ray observations of the spiral galaxy M81.
SWARTZ D.A., GHOSH K.K., McCOLLOUGH M.L., PANNUTI T.G., TENNANT A.F. and WU K.
Abstract (from CDS):
The non-nuclear point source population of M81 accounts for 88% of the non-nuclear X-ray luminosity of 8.1x1039 ergs.s–1. The remaining (unresolved) X-ray emission is confined within ∼2 kpc of the galactic center. The spatial distribution of this emission and of the resolved X-ray bulge sources closely follows that of the bulge optical light. In particular, there is no evidence for an X-ray signature accompanying the filamentary Hα or excess UV emission seen in the central ≲1.0 kpc of the galaxy. The shape of the luminosity function of the bulge sources is a power law with a break at ∼4x1037 ergs.s–1; suggesting the presence of an aging (∼400 Myr) population of low-mass X-ray binaries. Extrapolating this luminosity function to lower luminosities accounts for only ∼10% of the unresolved X-ray emission. Spectroscopically, the unresolved emission can be represented as a combination of soft, kT∼0.3 keV, optically thin plasma emission and of a Γ=1.6 power law. The unresolved bulge X-ray emission is therefore most likely a combination of hot gas and of one or more large and distinct populations of low-luminosity X-ray sources confined in the gravitational potential and tracing the old population of bulge stars. The distribution of disk sources shows a remarkably strong correlation with spiral arms with the brightest disk sources located closest to spiral arms. The luminosity function of sources near the spiral arms is a pure power law (slope -0.48±0.03), while that of sources further away exhibits a break or cutoff in the power-law distribution with no high-luminosity members. This is interpreted as a natural consequence of the passage of spiral density waves that leave the brightest (when averaged over their lifetimes) and shortest-lived X-ray sources immediately downstream of the spiral arms. Consistent with model predictions, we conclude that the shapes of the X-ray luminosity functions of the different galactic components of M81 are most likely governed by the birth rates and lifespans of their constituent X-ray source populations and that the luminosity functions can be used as a measure of the star formation histories of their environments.
Abstract Copyright: ∼
Journal keyword(s): Galaxies: Individual: Messier Number: M81 - Stars: Supernovae: Individual: Alphanumeric: SN 1993J - X-Rays: Binaries - X-Rays: Galaxies - X-Rays: Stars
VizieR on-line data: <Available at CDS (J/ApJS/144/213): table2.dat table3.dat>
Nomenclature: Table 2: [SGM2003] NNN (Nos 1-177).
Simbad objects: 187