Astrophys. J., 599, 218-236 (2003/December-2)
Chandra observations of low-mass X-ray binaries and diffuse gas in the early-type galaxies NGC 4365 and NGC 4382 (M85).
SIVAKOFF G.R., SARAZIN C.L. and IRWIN J.A.
Abstract (from CDS):
We used the Chandra X-Ray Observatory ACIS-S3 to image the X-ray-faint elliptical galaxy NGC 4365 and lenticular galaxy NGC 4382. The observations resolve much of the X-ray emission into 99 and 58 sources, respectively, most of which are low-mass X-ray binaries (LMXBs) associated with each of the galaxies. Within one effective radius of NGC 4365, about 45% of the counts are resolved into sources, 30% are attributed to unresolved LMXBs, and 25% are attributed to diffuse gas. Within two effective radii of NGC 4382, about 22% of the counts are resolved into sources, 33% are attributed to unresolved LMXBs, and 45% are attributed to diffuse gas. We identify 18 out of the 37 X-ray sources in a central field in NGC 4365 with globular clusters. The luminosity functions of the resolved sources for both galaxies are best fitted with cutoff power laws whose cutoff luminosity is ~(0.9-3.1)x1039 ergs/s. These luminosities are much larger than those previously measured for similar galaxies; we do not find evidence for a break in the luminosity function at the Eddington luminosity of a 1.4 M☉neutron star. The spatial distributions of the resolved sources for both galaxies are broader than the distribution of optical stars. In both galaxies, a hard power-law model fits the summed spectrum of all of the sources. The unresolved emission is best fitted by the sum of a soft MEKAL model, representing emission from diffuse gas, and a hard power law, presumed to be from unresolved LMXBs. There is some evidence that the temperature of the diffuse gas increases with increasing radius. A standard beta model fits the radial distribution of the diffuse gas in both galaxies. In the elliptical galaxy NGC 4365, the best-fit core radius is very small, while the S0 galaxy NGC 4382 has a larger core radius. This may indicate that the gas in NGC 4382 is rotating significantly.
Stars: Binaries: Close - Galaxies: Elliptical and Lenticular, cD - Galaxies: ISM - X-Rays: Binaries - X-Rays: Galaxies - X-Rays: ISM
VizieR on-line data:
<Available at CDS (J/ApJ/599/218): table1.dat table2.dat>
Table 1: [SSI2003b] NGC 4365 NN (Nos 1-99). Table 2: [SSI2003b] NGC 4382 NN (Nos 1-58).
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