2011ApJ...729...12B

We have selected a sample of 30 normal (non-cD) early-type galaxies, for all of which optical spectroscopy is available and which have been observed with Chandra to a depth such as to ensure the detection of bright low-mass X-ray binaries (LMXBs) with L_X> 10³⁸ erg/s. This sample includes a larger fraction of gas-poor galaxies than previously studied samples and covers a wide range of stellar luminosity (L_K), velocity dispersion (σ_*), globular cluster specific frequency (S_N), and stellar age. We derive X-ray luminosities (or upper limits) from the different significant X-ray components of these galaxies: nuclei, detected and undetected LMXBs, coronally active binaries (ABs), cataclysmic variables (CVs), and hot gas. The ABs and CVs contribution is estimated from the L_X-L_K scaling relation of M31 and M32. The contribution of undetected LMXBs is estimated both by fitting the spectra of the unresolved X-ray emission and by extrapolating the LMXB X-ray luminosity function. On average, the X-ray luminosity of LMXBs is a factor of ∼10 higher than that of ABs+CVs. By spectral fitting the emission (also considering gas emission in the regions of point sources), we estimate the contribution of the hot gas. We find our sample equally divided among galaxies with L_X(gas) > L_X(LMXB), L_X(ABCV) ≤ L_X(gas) ≤ L_X(LMXB), and L_X(gas) < L_X(ABCV). The results for the nuclei are consistent with those discussed by Pellegrini. We derive a revised scaling relation between the integrated X-ray luminosity of LMXBs in a galaxy and the L_Kluminosity of the host galaxy: L_X(LMXB)/L_K∼ 10²⁹ erg/s L_K^–1 with 50% 1σ rms; moreover, we also obtain a tighter L_X(LMXB)/L_K-S_Nrelation than previously published. We revisit the relations between hot gas content and other galaxy parameters (L_K, σ_*), which in most previous work was based on the integrated total X-ray luminosity of the galaxy, finding a steeper L_X(gas)-L_K relation with larger scatter than reported in the literature. We find a positive correlation between the luminosity and temperature of the hot interstellar medium, significantly tighter than reported by earlier studies. This relation is particularly well defined in the subsample with σ_*>240 km/s, where it may be related to the analogous correlation found in cD galaxies and groups/clusters. However, the gas-poor galaxies with the shallowest potentials (σ_*< 200 km/s) also follow this relation, contrary to the expected anti-correlation in a simple outflow/wind scenario. Galaxies with intermediate values of σ_* instead tend to have the same kT, while L_X(gas) spans a factor of ∼20; among these galaxies, we find a moderate, positive correlation between L_X(gas) and the average stellar age, possibly suggesting a transition from halo retention to outflow caused by rejuvenated star formation associated with recent mergers.