The Hot Gas Content of Low-Luminosity Early-Type Galaxies and the Implications Regarding Supernova Heating and AGN Feedback

Abstract

We have analyzed Chandra observations of 18 low-luminosity early-type galaxies with L_B < 3 x 10e10 Lo. Thermal emission from hot gas with temperatures between 0.2 and 0.8 keV comprises 5-70% of the total 0.5-2.0 keV emission from these galaxies. We find that the total X-ray luminosity from LMXBs (resolved plus the power-law component of the unresolved emission) scales roughly linearly with the K-band luminosity of the galaxies with a normalization comparable to that found in more luminous early-type galaxies. All of the galaxies in our sample are gas poor with gas masses much less than that expected from the accumulation of stellar mass loss over the life time of the galaxies. The average ratio of gas mass to stellar mass in our sample is M_{gas}/M_*=0.001, compared to more luminous early-type galaxies which typically have M_{gas}/M_*=0.01. The time required to accumulate the observed gas mass from stellar mass loss in these galaxies is typically 3 x 10e8 yr. Since the cooling time of the gas is longer than the replenishment time, the gas cannot be condensing out of the hot phase and forming stars, implying that the gas is most likely being expelled from these galaxies in a wind (abridged).