X-RAY SCALING RELATIONS OF “CORE” AND “CORELESS” E AND S0 GALAXIES

Abstract

We have re-examined the two X-ray scaling relations of early-type galaxies (ETGs), Lx - LK and Lx - T, using 61 ATLAS3D E and S0 galaxies observed with Chandra. The larger sample allows us to investigate the effect of structural and dynamical properties of ETGs in these relations. Using the sub-sample of genuine E galaxies with central surface brightness cores, slow stellar rotations and old stellar populations, we find that the scatter of the correlations is strongly reduced, yielding an extremely tight relation. For the gas-rich galaxies in this sample, this relation is consistent with recent simulations. However, the tight Lx - T relation of genuine E galaxies extends down into the Lx 1038 erg s-1 range, where simulations predict the gas to be in outflow/wind state. The observed correlation may suggest the presence of small bound hot halos even in this low luminosity range. At the high luminosity end, the Lx - T correlation of core elliptical galaxies is similar to that found in samples of cD galaxies and groups, but shifted down toward lower Lx. In particular cDs have an order of magnitude higher Lx than core galaxies for the same LK and T. We suggest that enhanced cooling in cDs could lower T to the range observed in giant Es; this conclusion is supported by the presence of extended cold gas in several cDs. Instead, in the sub-sample of coreless ETGs, Lx and T are not correlated, suggesting that both the energy input from star formation and the effect of galactic rotation and flattening may disrupt the hot ISM.