X‐Ray Properties of Early‐Type Galaxies as Observed withASCA

Abstract

We have systematically investigated the Advanced Satellite for Cosmology and Astrophysics (ASCA) spectra of 12 early-type galaxies. This paper presents the global spectral properties of these systems based on a larger sample than in any previous ASCA study. The X-ray spectra were uniformly Ðtted by a two-component model consisting of hard X-rays from thermal emission with a temperature of about 10 keV or from a power law with index 1.8, plus soft X-rays from a thin thermal plasma with temperature ranging from 0.3 to 1 keV. The X-ray luminosities of the hard component are found to be proportional to the blue-band luminosities, while those of the soft component show large scatter with no clear correlation. The metal abundances determined from the soft component are systematically lower than solar, with a mean value of about 0.3 solar. We examine the relationships between the temperature and volume emission measure and between the gas temperature and the stellar velocity dispersion. The volume emission measures for early-type galaxies plotted as a function of the gas temperature are well below the extrapolated line found in clusters of galaxies, indicating that early-type galaxies are relatively gas poor compared with galaxy clusters. The ratio of the stellar kinetic energy per unit mass to the thermal energy of the hot gas per unit mass is less than unity. We found no systematic relation-(b spec ) ship between X-ray properties and environment, suggesting that the interaction between interstellar matter and the intracluster medium is not strong.

The Declined Activity in the Nucleus of NGC 1316

“…which was first derived with Einstein (e.g., Forman et al 1985;Canizares et al 1987) and then updated using Ginga and ASCA (Makishima et al 1989;Matsushita et al 1994;Reynolds et al 1997;Matsumoto et al 1997). Since the correlation is thought to represent the dominant contribution of neutron star binaries to , we infer that the hard component of NGC hard L X 1316 is also dominated by the integrated emission from neutron star binaries, with little room for the LLAGN contribution.…”

“…Both these components are characteristic of elliptical galaxies, among which the former can be identified with the thermal emission from hot interstellar medium (ISM; e.g., Forman, Jones, & Tucker 1985;Canizares, Fabbiano, & Trinchieri 1987;Awaki et al 1994). The hard component is basically interpreted as integrated hard X-rays from neutron star binaries (e.g., Makishima et al 1989;Matsushita et al 1994;Matsumoto et al 1997) but may be partially contributed by the active nucleus, because AGN emission and the integrated X-ray binary emission often exhibit similar spectral shapes in the ASCA energy band.…”

The XMM-Newton view of the X-ray halo and jet of NGC 6251

“…The X-ray halo luminosity of NGC 6251 is two orders of magnitude larger than predicted by the L X − L B relationship in Fig. 6 of Matsumoto et al (1997). We assumed the halo luminosity given in Sect.…”

Apparent high metallicity in 3–4 keV galaxy clusters: the inverse iron-bias in action in the case of the merging cluster Abell 2028

“…Many ASCA studies found significant subsolar values for the iron abundance in groups and elliptical galaxies (e.g. Davis et al 1999;Matsumoto et al 1997), generally less than the stellar values in these systems and less than those observed in galaxy clusters. Buote (2000b) demonstrated that this was a bias resulting from fitting with a simple single-temperature a multi-temperature plasma, resulting in best-fitting elemental abundances that are too low.…”