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We present results from Chandra and XMM-Newton spectroscopic observations of the nuclei of z<0.5 radio galaxies and quasars from the 3CRR catalog, and examine in detail the dichotomy in the properties of low- and high-excitation radio galaxies. The X-ray spectra of low-excitation sources (those with weak or absent optical emission lines) are dominated by unabsorbed emission from a parsec-scale jet, with no contribution from accretion-related emission. These sources show no evidence for an obscuring torus, and are likely to accrete in a radiatively inefficient manner. High-excitation sources (those with prominent optical emission lines), on the other hand, show a significant contribution from a radiatively efficient accretion disk, which is heavily absorbed in the X-ray when they are oriented close to edge-on with respect to the observer. However, the low-excitation/high-excitation division does not correspond to the FRI/FRII division: thus the Fanaroff-Riley dichotomy remains a consequence of the interaction between the jet and the hot-gas environment through which it propagates. Finally, we suggest that accretion of the hot phase of the IGM is sufficient to power all low-excitation radio sources, while high-excitation sources require an additional contribution from cold gas that in turn forms the cold disk and torus. This model explains a number of properties of the radio-loud active galaxy population, and has important implications for AGN feedback mechanisms.
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Understanding the evolution of accretion activity is fundamental to our understanding of how galaxies form and evolve over the history of the Universe. We analyse a complete sample of 27 radio galaxies which includes both high-excitation (HEGs) and low excitation galaxies (LEGs), spanning a narrow redshift range of 0.9 < z < 1.1 and covering a factor of ~1000 in radio luminosity. Using data from the Spitzer Space Telescope combined with ground-based optical and near-infrared imaging, we show that the host galaxies have masses in the range of 10.7 < log (M /M_sun) < 12.0 with HEGs and LEGs exhibiting no difference in their mass distributions. We also find that HEGs accrete at significantly higher rates than LEGs, with the HEG/LEG division lying at an Eddington ratio of ~0.04, which is in excellent agreement with theoretical predictions of where the accretion rate becomes radiatively inefficient, thus supporting the idea of HEGs and LEGs being powered by different modes of accretion. Our study also shows that at least up to L_151MHz ~3x10^27 W /Hz /sr, HEGs and LEGs are indistinguishable in terms of their radio properties. From this result we infer that, at least for the lower radio luminosity range, another factor besides accretion rate must play an important role in the process of triggering jet activity.
We study the physical properties of three clusters of galaxies, selected from a BeppoSAX Wide Field Camera (WFC) survey. These sources are identified as 1RXS J153934.7-833535, 1RXS J160147.6-754507, and 1RXS J081232.3-571423 in the ROSAT All-Sky Survey catalogue. We obtained XMM-Newton follow-up observations for these three clusters. We fit single and multi-temperature models to spectra obtained from the EPIC-pn camera to determine the temperature, the chemical composition of the gas and their radial distribution. Since two observations are contaminated by a high soft-proton background, we develop a new method to estimate the effect of this background on the data. For the first time, we present the temperature and iron abundance of two of these three clusters. The iron abundance of 1RXS J153934.7-33535 decreases with radius. The fits to the XMM-Newton and Chandra data show that the radial temperature profile within 3 towards the centre either flattens or lowers. A Chandra image of the source suggests the presence of X-ray cavities. The gas properties in 1RXS J160147.6-754507 are consistent with a flat radial distribution of iron and temperature within 2 from the centre. 1RXS J081232.3-571423 is a relatively cool cluster with a temperature of about 3 keV. The radial temperature and iron profiles suggest that 1RXS J153934.7-833535 is a cool core cluster. The Chandra image shows substructure which points toward AGN feedback in the core. The flat radial profiles of the temperature and iron abundance in 1RXS J160147.6-754507 are similar to the profiles of non-cool-core clusters.
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 to insure the detection of bright low-mass X-ray binaries (LMXBs) with Lx>1e38 erg/s. This sample includes a larger fraction of gas-poor galaxies than previously studied samples, and covers a wide range of stellar luminosity, velocity dispersion, GC specific frequency, 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 Lx-LK 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. The results for the nuclei are consistent with those discussed by Pellegrini (2010). We derive a revised scaling relation between the integrated X-ray luminosity of LMXBs in a galaxy and the LK luminosity of the host galaxy: Lx(LMXB)/LK ~ 1e29 erg s-1 LK-1 with 50% 1sigma rms; moreover, we also obtain a tighter LX(LMXB)/LK - SN relation than previously published. We revisit the relations between hot gas content and other galaxy parameters. finding a steeper LX(gas)-LK relation with larger scatter than reported in the literature. We find a positive correlation between the luminosity and temperature of the hot ISM, significantly tighter than reported by earlier studies.[abridged]
We investigate trends of the cold and hot gas content of early-type galaxies with the presence of optical morphological peculiarities, as measured by the fine-structure index (Sigma). HI mapping observations from the literature are used to track the cold-gas content, and archival ROSAT PSPC data are used to quantify the hot-gas content. We find that E and S0 galaxies with a high incidence of optical peculiarities are exclusively X-ray underluminous and, therefore, deficient in hot gas. In contrast, more relaxed galaxies with little or no signs of optical peculiarities span a wide range of X-ray luminosities. That is, the X-ray excess anticorrelates with Sigma. There appears to be no similar trend of cold-gas content with either fine-structure index or X-ray content. The fact that only apparently relaxed E and S0 galaxies are strong X-ray emitters is consistent with the hypothesis that after strong disturbances such as a merger hot-gas halos build up over a time scale of several gigayears. This is consistent with the expected mass loss from stars.
We present a systematic study of the diffuse hot gas around early-type galaxies (ETGs) residing in the Virgo cluster, based on archival {it Chandra} observations. Our representative sample consists of 79 galaxies with low-to-intermediate stellar masses ($M_* approx 10^{9-11}rm~M_odot$), a mass range that has not been extensively explored with X-ray observations thus far. We detect diffuse X-ray emission in only eight galaxies and find that in five cases a substantial fraction of the detected emission can be unambiguously attributed to truly diffuse hot gas, based on their spatial distribution and spectral properties. For the individually non-detected galaxies, we constrain their average X-ray emission by performing a stacking analysis, finding a specific X-ray luminosity of $L_{rm X}/M_* sim 10^{28}{rm~erg~s^{-1}~M_{odot}^{-1}}$, which is consistent with unresolved stellar populations. The apparent paucity of truly diffuse hot gas in these low- and intermediate-mass ETGs may be the result of efficient ram pressure stripping by the hot intra-cluster medium. However, we also find no significant diffuse hot gas in a comparison sample of 57 field ETGs of similar stellar masses, for which archival {it Chandra} observations with similar sensitivity are available. This points to the alternative possibility that galactic winds evacuate the hot gas from the inner region of low- and intermediate-mass ETGs, regardless of the galactic environment. Nevertheless, we do find strong morphological evidence for on-going ram pressure stripping in two galaxies (NGC 4417 and NGC 4459). A better understanding of the roles of ram pressure stripping and galactic winds in regulating the hot gas content of ETGs, invites sensitive X-ray observations for a large galaxy sample.
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