2015ApJ...812..127K

We have re-examined the two X-ray scaling relations of early-type galaxies (ETGs), L_X,GAS-L_K and L_X,GAS-T_GAS, using 61 ATLAS^3D E and S0 galaxies observed with Chandra (including ROSAT results for a few X-ray bright galaxies with extended hot gas). With this sample, which doubles the number of ETGs available for study we confirm the strong, steep correlations reported by Boroson et al. Moreover, the larger sample allows us to investigate the effect of structural and dynamical properties of ETGs in these relations. Using the sub-sample of 11 ''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 of the form L_X,GAS∼ The rms deviation is only 0.13 dex. For the gas-rich galaxies in this sample (L_X,GAS> 10⁴⁰ erg/s), this relation is consistent with recent simulations for velocity dispersion supported E galaxies. However, the tight L_X,GAS-T_GAS relation of genuine E galaxies extends down into the L_X∼ 10³⁸ erg/s range, where simulations predict the gas to be in outflow/wind state, with resulting L_Xmuch lower than observed in our sample. The observed correlation may suggest the presence of small bound hot halos even in this low luminosity range. At the high luminosity end, the L_X,GAS-T_GAScorrelation of core elliptical galaxies is similar to that found in samples of cD galaxies and groups, but shifted down toward relatively lower L_X,GASfor a given T_GAS. In particular cDs, central dominant galaxies sitting at the bottom of the potential well imposed by the group dark matter, have an order of magnitude higher L_X,GASthan our sample core galaxies for the same L_Kand T_GAS. We suggest that enhanced cooling in cDs, which have higher hot gas densities and lower entropies, could lower T_GASto 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–these galaxies also tend to show stellar rotation, a flattened galaxy figure and rejuvenation of the stellar population–L_X,GAS and T_GASare not correlated. The L_X-T_GASdistribution of coreless ETGs is a scatter diagram clustered at L_X,GAS< 10⁴⁰ erg/s, similar to that reported for the hot interstellar medium (ISM) of spiral galaxies, suggesting that both the energy input from star formation and the effect of galactic rotation and flattening may disrupt the hot ISM.