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We have analyzed the Chandra archival data of NGC 1132, a well-known fossil group, i.e., a system expected to be old and relaxed long after the giant elliptical galaxy assembly. Instead, the Chandra data reveal that the hot gas morphology is disturbed and asymmetrical, with a cold front following a possible bow shock. We discuss possible origins of the disturbed hot halo, including sloshing by a nearby object, merger, ram pressure by external hotter gas, and nuclear outburst. We consider that the first two mechanisms are likely explanations for the disturbed hot halo, with a slight preference for a minor merger with a low impact parameter because of the match with simulations and previous optical observations. In this case, NGC 1132 may be a rare example of unusual late mergers seen in recent simulations. Regardless of the origin of the disturbed hot halo, the paradigm of the fossil system needs to be reconsidered. [ABSTRACT FROM AUTHOR]

We present results of a joint Chandra/XMM-Newton analysis of the early-type galaxies NGC 4649 and NGC 5846 aimed at investigating differences between mass profiles derived from X-ray data and those from optical data, to probe the state of the hot interstellar medium (ISM) in these galaxies. If the hot ISM is at a given radius in hydrostatic equilibrium (HE), the X-ray data can be used to measure the total enclosed mass of the galaxy. Differences from optically derived mass distributions therefore yield information about departures from HE in the hot halos. The X-ray mass profiles in different angular sectors of NGC 4649 are generally smooth with no significant azimuthal asymmetries within 12 kpc. Extrapolation of these profiles beyond this scale yields results consistent with the optical estimate. However, in the central region ( kpc) the X-ray data underpredict the enclosed mass, when compared with the optical mass profiles. Consistent with previous results, we estimate a nonthermal pressure component accounting for 30% of the gas pressure, likely linked to nuclear activity. In NGC 5846 the X-ray mass profiles show significant azimuthal asymmetries, especially in the NE direction. Comparison with optical mass profiles in this direction suggests significant departures from HE, consistent with bulk gas compression and decompression due to sloshing on ∼15 kpc scales; this effect disappears in the NW direction, where the emission is smooth and extended. In this sector we find consistent X-ray and optical mass profiles, suggesting that the hot halo is not responding to strong nongravitational forces. [ABSTRACT FROM AUTHOR]

We present a stacking analysis of the complete sample of early-type galaxies (ETGs) in the Chandra COSMOS (C-COSMOS) survey, to explore the nature of the X-ray luminosity in the redshift and stellar luminosity ranges and . Using established scaling relations, we subtract the contribution of X-ray binary populations to estimate the combined emission of hot ISM and active galactic nuclei (AGNs). To discriminate between the relative importance of these two components, we (1) compare our results with the relation observed in the local universe for hot gaseous halos emission in ETGs, and (2) evaluate the spectral signature of each stacked bin. We find two regimes where the non-stellar X-ray emission is hard, consistent with AGN emission. First, there is evidence of hard, absorbed X-ray emission in stacked bins including relatively high z (∼1.2) ETGs with average high X-ray luminosity (). These luminosities are consistent with the presence of highly absorbed “hidden” AGNs in these ETGs, which are not visible in their optical–IR spectra and spectral energy distributions. Second, confirming the early indication from our C-COSMOS study of X-ray detected ETGs, we find significantly enhanced X-ray luminosity in lower stellar mass ETGs (), relative to the local relation. The stacked spectra of these ETGs also suggest X-ray emission harder than expected from gaseous hot halos. This emission is consistent with inefficient accretion onto . [ABSTRACT FROM AUTHOR]

We have re-examined the two X-ray scaling relations of early-type galaxies (ETGs), LX,GAS–LK and LX,GAS–TGAS, using 61 ATLAS3D 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 LX,GAS ∼ The rms deviation is only 0.13 dex. For the gas-rich galaxies in this sample (LX,GAS > 1040 erg s−1), this relation is consistent with recent simulations for velocity dispersion supported E galaxies. However, the tight LX,GAS–TGAS 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, with resulting LX much 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 LX,GAS–TGAS correlation of core elliptical galaxies is similar to that found in samples of cD galaxies and groups, but shifted down toward relatively lower LX,GAS for a given TGAS. 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 LX,GAS than our sample core galaxies for the same LK and TGAS. We suggest that enhanced cooling in cDs, which have higher hot gas densities and lower entropies, could lower TGAS 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—these galaxies also tend to show stellar rotation, a flattened galaxy figure and rejuvenation of the stellar population—LX,GAS and TGAS are not correlated. The LX−TGAS distribution of coreless ETGs is a scatter diagram clustered at LX,GAS < 1040 erg s−1, 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. [ABSTRACT FROM AUTHOR]