Metal Abundance of an X-Ray Emitting Gas in Two Groups of Galaxies: The NGC 5044 Group and HCG 51

Abstract

We observed two groups of galaxies, the NGC 5044 group (WP 23) and Hickson's compact group HCG 51, with ASCA. We detected an extended bright soft X-ray emission, which indicates the existence of large amounts of a hot X-ray emitting gas in both targets. The temperature of the hot gas is ∼ 1 keV for both objects, which is equivalent to their galaxy velocity dispersion. The metal abundance of the gas is 0.3–0.5 solar value for both objects, which is similar to that of rich clusters of galaxies. The Si to Fe abundance ratio is smaller than that of rich clusters of galaxies, although the iron abundances determined by the Fe-L lines are somewhat uncertain. The X-ray luminosities in the 0.5–10 keV band are 1 × 1043 erg s−1 and 5 × 1042 erg s−1 for the NGC 5044 group and HCG 51, respectively, which are higher by an order of magnitude than those of X-ray bright elliptical galaxies. This makes HCG 51 one of the most X-ray luminous compact groups. Both objects have a total gravitating mass of Mtotal ∼ 2.0 × 1013M⊙, and a gas mass and a galaxy mass of Mgas ∼ Mgalaxy ∼ 1.5 × 1012M⊙. The ratios among these mass components are Mgas/Mgalaxy ∼ 1 and (Mgas + Mgalaxy)/ Mtotal ∼ 0.2 within ∼ 350 kpc for both objects. The latter is similar to previous ROSAT results for many groups of galaxies, while the former is larger than the average value of the ROSAT-observed groups. Moreover, the metal abundances of the present two groups are significantly higher than those of the NGC 2300 group and HCG 62, and are comparable to those of clusters. These suggest that the hot-gas mass and metal abundances can scatter widely among groups, compared to the small variance found among rich clusters.

Constraining the role of Type Ia and Type II supernovae in galaxy groups by spatially resolved analysis of ROSAT and ASCA observations

“…The analysis presented in this paper differs from previous work on these objects (e.g. Fukazawa et al 1996), which have generally ignored the effects of projection and PSF blurring. Since the PSF is energy-dependent, simpli®ed analyses can give misleading results (Takahashi et al 1995).…”

Statistical properties of metal abundances of the intracluster medium in the central region of clusters

“…We also plot results given by the Mekal and Masai codes, in order to investigate the dependence on the plasma codes (e.g. Fabian et al 1994b;Fukazawa et al 1996) in Fig. 7.…”

Search for hot gas in the local group with ASCA

“…The metal abundance was fixed to 0.3 solar based on results for other groups (Mulchaey et al 1996;Fukazawa et al 1996;Hickson 1997;Mulchaey, Zabludoff 1998). We fixed the plasma temperature in the range of 0.3-1.2 keV, stepping by 0.1 keV, to cover the typical values found in groups of galaxies (Pilidis et al 1995;Fukazawa et al 1996;Mulchaey et al 1996;Mulchaey, Zabludoff 1998;Davis et al 1999;Takahashi et al 2000). Although the small velocity dispersion, about 60 km s −1 , of the Local Group might indicate a considerably lower temperature (e.g., ∼ 0.1 keV) for a hydrostatic hot gas, the GIS does not have sensitivity for such cool emission.…”