We study the evolution of the total star formation (SF) activity, total stellar mass (Sigma M-*) and halo occupation distribution (HOD) in massive haloes by using one of the largest X-ray selected sample of galaxy groups with secure spectroscopic identification in the major blank field surveys (ECDFS, CDFN, COSMOS, AEGIS). We provide an accurate measurement of star formation rate (SFR) for the bulk of the star-forming galaxies using very deep mid-infrared Spitzer MIPS and far-infrared Herschel PACS observations. For undetected IR sources, we provide a well-calibrated SFR from spectral energy distribution (SED) fitting. We observe a clear evolution in the level of SF activity in galaxy groups. The total SF activity in the high-redshift groups (0.5 < z < 1.1) is higher with respect to the low-redshift (0.15 < z < 0.5) sample at any mass by 0.8 +/- 0.12 dex. A milder difference (0.35 +/- 0.1 dex) is observed between the low-redshift bin and the groups at z similar to 0. We show that the level of SF activity is declining more rapidly in the more massive haloes than in the more common lower mass haloes. We do not observe any evolution in the HOD and total stellar mass-halo mass relations in groups. The picture emerging from our findings suggests that the galaxy population in the most massive systems is evolving faster than galaxies in lower mass haloes, consistently with a 'halo downsizing' scenario.

We study the evolution of the total star formation (SF) activity, total stellar mass (Sigma M-*) and halo occupation distribution (HOD) in massive haloes by using one of the largest X-ray selected sample of galaxy groups with secure spectroscopic identification in the major blank field surveys (ECDFS, CDFN, COSMOS, AEGIS). We provide an accurate measurement of star formation rate (SFR) for the bulk of the star-forming galaxies using very deep mid-infrared Spitzer MIPS and far-infrared Herschel PACS observations. For undetected IR sources, we provide a well-calibrated SFR from spectral energy distribution (SED) fitting. We observe a clear evolution in the level of SF activity in galaxy groups. The total SF activity in the high-redshift groups (0.5 < z < 1.1) is higher with respect to the low-redshift (0.15 < z < 0.5) sample at any mass by 0.8 +/- 0.12 dex. A milder difference (0.35 +/- 0.1 dex) is observed between the low-redshift bin and the groups at z similar to 0. We show that the level of SF activity is declining more rapidly in the more massive haloes than in the more common lower mass haloes. We do not observe any evolution in the HOD and total stellar mass-halo mass relations in groups. The picture emerging from our findings suggests that the galaxy population in the most massive systems is evolving faster than galaxies in lower mass haloes, consistently with a 'halo downsizing' scenario.

We study the evolution of the total star formation (SF) activity, total stellar mass (Sigma M-*) and halo occupation distribution (HOD) in massive haloes by using one of the largest X-ray selected sample of galaxy groups with secure spectroscopic identification in the major blank field surveys (ECDFS, CDFN, COSMOS, AEGIS). We provide an accurate measurement of star formation rate (SFR) for the bulk of the star-forming galaxies using very deep mid-infrared Spitzer MIPS and far-infrared Herschel PACS observations. For undetected IR sources, we provide a well-calibrated SFR from spectral energy distribution (SED) fitting. We observe a clear evolution in the level of SF activity in galaxy groups. The total SF activity in the high-redshift groups (0.5 < z < 1.1) is higher with respect to the low-redshift (0.15 < z < 0.5) sample at any mass by 0.8 +/- 0.12 dex. A milder difference (0.35 +/- 0.1 dex) is observed between the low-redshift bin and the groups at z similar to 0. We show that the level of SF activity is declining more rapidly in the more massive haloes than in the more common lower mass haloes. We do not observe any evolution in the HOD and total stellar mass-halo mass relations in groups. The picture emerging from our findings suggests that the galaxy population in the most massive systems is evolving faster than galaxies in lower mass haloes, consistently with a 'halo downsizing' scenario.

We present a study of extended galaxy halo gas through H I and O VI absorption over two decades in projected distance at z approximate to 0.2. The study is based on a sample of 95 galaxies from a highly complete (> 80 per cent) survey of faint galaxies (L > 0.1L(*)) with archival quasar absorption spectra and 53 galaxies from the literature. A clear anticorrelation is found between H I (O VI) column density and virial radius normalized projected distance, d/R-h. Strong H I (O VI) absorption systems with column densities greater than 10(14.0) (10(13.5)) cm(-2) are found for 48 of 54 (36 of 42) galaxies at d < R-h indicating a mean covering fraction of = 0.89 ( = 0.86). O VI absorbers are found at d approximate to R-h, beyond the extent observed for lower ionization species. At d/R-h = 1-3 strong H I (O VI) absorption systems are found for only 7 of 43 (5 of 34) galaxies ( = 0.16 and = 0.15). Beyond d = 3 R-h, the H I and O VI covering fractions decrease to levels consistent with coincidental systems. The high completeness of the galaxy survey enables an investigation of environmental dependence of extended gas properties. Galaxies with nearby neighbours exhibit a modest increase in O VI covering fraction at d > R-h compared to isolated galaxies (kappa(O) (VI) approximate to 0.13 versus 0.04) but no excess H I absorption. These findings suggest that environmental effects play a role in distributing heavy elements beyond the enriched gaseous haloes of individual galaxies. Finally, we find that differential H I and O VI absorption between early-and late-type galaxies continues from d < R-h to d approximate to 3 R-h.

We present a study of extended galaxy halo gas through H I and O VI absorption over two decades in projected distance at z approximate to 0.2. The study is based on a sample of 95 galaxies from a highly complete (> 80 per cent) survey of faint galaxies (L > 0.1L(*)) with archival quasar absorption spectra and 53 galaxies from the literature. A clear anticorrelation is found between H I (O VI) column density and virial radius normalized projected distance, d/R-h. Strong H I (O VI) absorption systems with column densities greater than 10(14.0) (10(13.5)) cm(-2) are found for 48 of 54 (36 of 42) galaxies at d < R-h indicating a mean covering fraction of = 0.89 ( = 0.86). O VI absorbers are found at d approximate to R-h, beyond the extent observed for lower ionization species. At d/R-h = 1-3 strong H I (O VI) absorption systems are found for only 7 of 43 (5 of 34) galaxies ( = 0.16 and = 0.15). Beyond d = 3 R-h, the H I and O VI covering fractions decrease to levels consistent with coincidental systems. The high completeness of the galaxy survey enables an investigation of environmental dependence of extended gas properties. Galaxies with nearby neighbours exhibit a modest increase in O VI covering fraction at d > R-h compared to isolated galaxies (kappa(O) (VI) approximate to 0.13 versus 0.04) but no excess H I absorption. These findings suggest that environmental effects play a role in distributing heavy elements beyond the enriched gaseous haloes of individual galaxies. Finally, we find that differential H I and O VI absorption between early-and late-type galaxies continues from d < R-h to d approximate to 3 R-h.

We present a study of extended galaxy halo gas through H I and O VI absorption over two decades in projected distance at z approximate to 0.2. The study is based on a sample of 95 galaxies from a highly complete (> 80 per cent) survey of faint galaxies (L > 0.1L(*)) with archival quasar absorption spectra and 53 galaxies from the literature. A clear anticorrelation is found between H I (O VI) column density and virial radius normalized projected distance, d/R-h. Strong H I (O VI) absorption systems with column densities greater than 10(14.0) (10(13.5)) cm(-2) are found for 48 of 54 (36 of 42) galaxies at d < R-h indicating a mean covering fraction of = 0.89 ( = 0.86). O VI absorbers are found at d approximate to R-h, beyond the extent observed for lower ionization species. At d/R-h = 1-3 strong H I (O VI) absorption systems are found for only 7 of 43 (5 of 34) galaxies ( = 0.16 and = 0.15). Beyond d = 3 R-h, the H I and O VI covering fractions decrease to levels consistent with coincidental systems. The high completeness of the galaxy survey enables an investigation of environmental dependence of extended gas properties. Galaxies with nearby neighbours exhibit a modest increase in O VI covering fraction at d > R-h compared to isolated galaxies (kappa(O) (VI) approximate to 0.13 versus 0.04) but no excess H I absorption. These findings suggest that environmental effects play a role in distributing heavy elements beyond the enriched gaseous haloes of individual galaxies. Finally, we find that differential H I and O VI absorption between early-and late-type galaxies continues from d < R-h to d approximate to 3 R-h.

Aims. We present the detection, identification and calibration of extended sources in the deepest X-ray dataset to date, the Extended Chandra Deep Field South (ECDF-S).

Aims. We present the detection, identification and calibration of extended sources in the deepest X-ray dataset to date, the Extended Chandra Deep Field South (ECDF-S).

Aims. We present the detection, identification and calibration of extended sources in the deepest X-ray dataset to date, the Extended Chandra Deep Field South (ECDF-S).

Previous observations of quasar host haloes at z approximate to 2 have uncovered large quantities of cool gas that exceed what is found around inactive galaxies of both lower and higher masses. To better understand the source of this excess cool gas, we compiled an exhaustive sample of 195 quasars at z approximate to 1 with constraints on chemically enriched, cool gas traced by MgII absorption in background quasar spectra from the Sloan Digital Sky Survey. This quasar sample spans a broad range of luminosities from L-bol = 10(44.4) to 10(46.8) erg s(-1) and allows an investigation of whether halo gas properties are connected with quasar properties. We find a strong correlation between luminosity and cool gas covering fraction. In particular, low-luminosity quasars exhibit a mean gas covering fraction comparable to inactive galaxies of similar masses, but more luminous quasars exhibit excess cool gas approaching what is reported previously at z approximate to 2. Moreover, 30-40 per cent of the Mg II absorption occurs at radial velocities of vertical bar Delta nu vertical bar > 300 km s(-1) from the quasar, inconsistent with gas bound to a typical quasar host halo. The large velocity offsets and observed luminosity dependence of the cool gas near quasars can be explained if the gas arises from: (1) neighbouring haloes correlated through large-scale structure at Mpc scales, (2) feedback from luminous quasars or (3) debris from the mergers thought to trigger luminous quasars. The first of these scenarios is in tension with the lack of correlation between quasar luminosity and clustering while the latter two make distinct predictions that can be tested with additional observations.