The Influence of Central Stellar Density and External Pressure on Gas Flows in Ellipticals

Abstract

In a recent paper (D’Ercole et al. 1989) we have presented a set of hydrodynamical models describing the evolution of the X-ray gas in elliptical galaxies. As usual, the gas is shed by the evolving stars at a rate α_*(t) and heated to X-ray temperatures (T ~ 1O⁷ K) by type I supernovae occurring at the rate R _SN(t). Unlike previous time dependent models (Loewenstein and Mathews 1987), we assume that R _SN decreases with time slightly faster than α_*; in this way the global supernova heating — hereafter SN luminosity L _SN — is initially sufficient to extract from the galaxy the gas lost by the stars, a supersonic wind is established which slowly evolves into a subsonic outflow. Later, an inflow can eventually be established, similar to that of ordinary cooling-flow models (e.g. Sarazin and White 1988). Contrary to the cooling flow approximation, this kind of models permits to account for the large scatter in X-ray luminosity L _X for given optical luminosity L _B, as well as to avoid an excessive concentration of matter in the center of the galaxy (D’Ercole et al. 1989; Ciotti et al. 1989; Renzini, this volume). Here we present additional models addressing two specific questions: 1) the effects of the density distribution near the center of the model galaxies, and 2) the effects of the external pressure due to the intracluster gas.