We examine galaxy groups from the present epoch to z similar to 1 to explore the impact of group dynamics on galaxy evolution. We use group catalogues from the Sloan Digital Sky Survey (SDSS), the Group Environment and Evolution Collaboration (GEEC) and the high-redshift GEEC2 samples to study how the observed member properties depend on the galaxy stellar mass, group dynamical mass and dynamical state of the host group. We find a strong correlation between the fraction of non-star-forming (quiescent) galaxies and galaxy stellar mass, but do not detect a significant difference in the quiescent fraction with group dynamical mass, within our sample halo mass range of similar to 10(13)-10(14.5) M-circle dot, or with dynamical state. However, at z similar to 0.4 we do find some evidence that the quiescent fraction in low-mass galaxies [log(10)(M-star/M-circle dot) less than or similar to 10.5] is lower in groups with substructure. Additionally, our results show that the fraction of groups with non-Gaussian velocity distributions increases with redshift to z similar to 0.4, while the amount of detected substructure remains constant to z similar to 1. Based on these results, we conclude that for massive galaxies [log(10)(M-star/M-circle dot) greater than or similar to 10.5], evolution is most strongly correlated to the stellar mass of a galaxy with little or no additional effect related to either the group dynamical mass or the dynamical state. For low-mass galaxies, we do find some evidence of a correlation between the quiescent fraction and the amount of detected substructure, highlighting the need to probe further down the stellar mass function to elucidate the role of environment in galaxy evolution.

We examine galaxy groups from the present epoch to z similar to 1 to explore the impact of group dynamics on galaxy evolution. We use group catalogues from the Sloan Digital Sky Survey (SDSS), the Group Environment and Evolution Collaboration (GEEC) and the high-redshift GEEC2 samples to study how the observed member properties depend on the galaxy stellar mass, group dynamical mass and dynamical state of the host group. We find a strong correlation between the fraction of non-star-forming (quiescent) galaxies and galaxy stellar mass, but do not detect a significant difference in the quiescent fraction with group dynamical mass, within our sample halo mass range of similar to 10(13)-10(14.5) M-circle dot, or with dynamical state. However, at z similar to 0.4 we do find some evidence that the quiescent fraction in low-mass galaxies [log(10)(M-star/M-circle dot) less than or similar to 10.5] is lower in groups with substructure. Additionally, our results show that the fraction of groups with non-Gaussian velocity distributions increases with redshift to z similar to 0.4, while the amount of detected substructure remains constant to z similar to 1. Based on these results, we conclude that for massive galaxies [log(10)(M-star/M-circle dot) greater than or similar to 10.5], evolution is most strongly correlated to the stellar mass of a galaxy with little or no additional effect related to either the group dynamical mass or the dynamical state. For low-mass galaxies, we do find some evidence of a correlation between the quiescent fraction and the amount of detected substructure, highlighting the need to probe further down the stellar mass function to elucidate the role of environment in galaxy evolution.

We present new absorption-line analysis and new galaxy survey data obtained for the field around PKS 0405-123 at z(QSO) = 0.57. Combining previously known O vi absorbers with new identifications in the higher S/N ultraviolet (UV) spectra obtained with the Cosmic Origins Spectrograph, we have established a sample of 7 O vi absorbers and 12 individual components at z = 0.0918-0.495 along the sightline towards PKS 0405-123. We complement the available UV absorption spectra with galaxy survey data that reach 100 per cent completeness at projected distances < 200 kpc of the quasar sightline for galaxies as faint as 0.1 L-* (0.2 L-*) out to redshifts of z approximate to 0.35 (z approximate to 0.5). The high level of completeness achieved at faint magnitudes by our survey reveals that O vi absorbers are closely associated with gas-rich environments containing at least one low-mass, emission-line galaxy. An intriguing exception is a strong O vi system at z approximate to 0.183 that does not have a galaxy found at < 4 Mpc, and our survey rules out the presence of any galaxies of L > 0.04 L-* at < 250 kpc and any galaxies of L > 0.3 L-* at < 1 Mpc. We further examine the galactic environments of O vi absorbers and those 'Ly alpha-only' absorbers with neutral hydrogen column density log N(Hi < 13.6 and no detectable O vi absorption features. The Ly alpha-only absorbers serve as a control sample in seeking the discriminating galactic features that result in the observed O vi absorbing gas at large galactic radii. We find a clear distinction in the radial profiles of mean galaxy surface brightness around different absorbers. Specifically, O vi absorbers are found to reside in regions of higher mean surface brightness at less than or similar to 500 kpc (delta mu(R) approximate to +5 mag Mpc(-2) relative to the background at > 500 kpc), while only a mild increase in galaxy surface brightness is seen at small around Ly alpha-only absorbers (delta mu(R) approximate to +2 mag Mpc(-2)). The additional insights gained from our deep galaxy survey demonstrate the need to probe the galaxy populations to low luminosities in order to better understand the nature of the absorbing systems.

We present new absorption-line analysis and new galaxy survey data obtained for the field around PKS 0405-123 at z(QSO) = 0.57. Combining previously known O vi absorbers with new identifications in the higher S/N ultraviolet (UV) spectra obtained with the Cosmic Origins Spectrograph, we have established a sample of 7 O vi absorbers and 12 individual components at z = 0.0918-0.495 along the sightline towards PKS 0405-123. We complement the available UV absorption spectra with galaxy survey data that reach 100 per cent completeness at projected distances < 200 kpc of the quasar sightline for galaxies as faint as 0.1 L-* (0.2 L-*) out to redshifts of z approximate to 0.35 (z approximate to 0.5). The high level of completeness achieved at faint magnitudes by our survey reveals that O vi absorbers are closely associated with gas-rich environments containing at least one low-mass, emission-line galaxy. An intriguing exception is a strong O vi system at z approximate to 0.183 that does not have a galaxy found at < 4 Mpc, and our survey rules out the presence of any galaxies of L > 0.04 L-* at < 250 kpc and any galaxies of L > 0.3 L-* at < 1 Mpc. We further examine the galactic environments of O vi absorbers and those 'Ly alpha-only' absorbers with neutral hydrogen column density log N(Hi < 13.6 and no detectable O vi absorption features. The Ly alpha-only absorbers serve as a control sample in seeking the discriminating galactic features that result in the observed O vi absorbing gas at large galactic radii. We find a clear distinction in the radial profiles of mean galaxy surface brightness around different absorbers. Specifically, O vi absorbers are found to reside in regions of higher mean surface brightness at less than or similar to 500 kpc (delta mu(R) approximate to +5 mag Mpc(-2) relative to the background at > 500 kpc), while only a mild increase in galaxy surface brightness is seen at small around Ly alpha-only absorbers (delta mu(R) approximate to +2 mag Mpc(-2)). The additional insights gained from our deep galaxy survey demonstrate the need to probe the galaxy populations to low luminosities in order to better understand the nature of the absorbing systems.

We present new absorption-line analysis and new galaxy survey data obtained for the field around PKS 0405-123 at z(QSO) = 0.57. Combining previously known O vi absorbers with new identifications in the higher S/N ultraviolet (UV) spectra obtained with the Cosmic Origins Spectrograph, we have established a sample of 7 O vi absorbers and 12 individual components at z = 0.0918-0.495 along the sightline towards PKS 0405-123. We complement the available UV absorption spectra with galaxy survey data that reach 100 per cent completeness at projected distances < 200 kpc of the quasar sightline for galaxies as faint as 0.1 L-* (0.2 L-*) out to redshifts of z approximate to 0.35 (z approximate to 0.5). The high level of completeness achieved at faint magnitudes by our survey reveals that O vi absorbers are closely associated with gas-rich environments containing at least one low-mass, emission-line galaxy. An intriguing exception is a strong O vi system at z approximate to 0.183 that does not have a galaxy found at < 4 Mpc, and our survey rules out the presence of any galaxies of L > 0.04 L-* at < 250 kpc and any galaxies of L > 0.3 L-* at < 1 Mpc. We further examine the galactic environments of O vi absorbers and those 'Ly alpha-only' absorbers with neutral hydrogen column density log N(Hi < 13.6 and no detectable O vi absorption features. The Ly alpha-only absorbers serve as a control sample in seeking the discriminating galactic features that result in the observed O vi absorbing gas at large galactic radii. We find a clear distinction in the radial profiles of mean galaxy surface brightness around different absorbers. Specifically, O vi absorbers are found to reside in regions of higher mean surface brightness at less than or similar to 500 kpc (delta mu(R) approximate to +5 mag Mpc(-2) relative to the background at > 500 kpc), while only a mild increase in galaxy surface brightness is seen at small around Ly alpha-only absorbers (delta mu(R) approximate to +2 mag Mpc(-2)). The additional insights gained from our deep galaxy survey demonstrate the need to probe the galaxy populations to low luminosities in order to better understand the nature of the absorbing systems.

We present new absorption-line analysis and new galaxy survey data obtained for the field around PKS 0405-123 at z(QSO) = 0.57. Combining previously known O vi absorbers with new identifications in the higher S/N ultraviolet (UV) spectra obtained with the Cosmic Origins Spectrograph, we have established a sample of 7 O vi absorbers and 12 individual components at z = 0.0918-0.495 along the sightline towards PKS 0405-123. We complement the available UV absorption spectra with galaxy survey data that reach 100 per cent completeness at projected distances < 200 kpc of the quasar sightline for galaxies as faint as 0.1 L-* (0.2 L-*) out to redshifts of z approximate to 0.35 (z approximate to 0.5). The high level of completeness achieved at faint magnitudes by our survey reveals that O vi absorbers are closely associated with gas-rich environments containing at least one low-mass, emission-line galaxy. An intriguing exception is a strong O vi system at z approximate to 0.183 that does not have a galaxy found at < 4 Mpc, and our survey rules out the presence of any galaxies of L > 0.04 L-* at < 250 kpc and any galaxies of L > 0.3 L-* at < 1 Mpc. We further examine the galactic environments of O vi absorbers and those 'Ly alpha-only' absorbers with neutral hydrogen column density log N(Hi < 13.6 and no detectable O vi absorption features. The Ly alpha-only absorbers serve as a control sample in seeking the discriminating galactic features that result in the observed O vi absorbing gas at large galactic radii. We find a clear distinction in the radial profiles of mean galaxy surface brightness around different absorbers. Specifically, O vi absorbers are found to reside in regions of higher mean surface brightness at less than or similar to 500 kpc (delta mu(R) approximate to +5 mag Mpc(-2) relative to the background at > 500 kpc), while only a mild increase in galaxy surface brightness is seen at small around Ly alpha-only absorbers (delta mu(R) approximate to +2 mag Mpc(-2)). The additional insights gained from our deep galaxy survey demonstrate the need to probe the galaxy populations to low luminosities in order to better understand the nature of the absorbing systems.

In the local Universe, galaxy properties show a strong dependence on environment. In cluster cores, early-type galaxies dominate, whereas star-forming galaxies are more and more common in the outskirts. At higher redshifts and in somewhat less dense environments (e.g. galaxy groups), the situation is less clear. One open issue is that of whether and how the star formation rate (SFR) of galaxies in groups depends on the distance from the centre of mass. To shed light on this topic, we have built a sample of X-ray selected galaxy groups at 0 < z < 1.6 in various blank fields [Extended Chandra Deep Field South (ECDFS), Cosmological Evolution Survey (COSMOS), Great Observatories Origin Deep Survey (GOODS)]. We use a sample of spectroscopically confirmed group members with stellar mass M-star > 10(10.3) M-circle dot in order to have a high spectroscopic completeness. As we use only spectroscopic redshifts, our results are not affected by uncertainties due to projection effects. We use several SFR indicators to link the star formation (SF) activity to the galaxy environment. Taking advantage of the extremely deep mid-infrared Spitzer MIPS and far-infrared Herschel(1) PACS observations, we have an accurate, broad-band measure of the SFR for the bulk of the star-forming galaxies. We use multi-wavelength Spectral Energy Distribution (SED) fitting techniques to estimate the stellar masses of all objects and the SFR of the MIPS and PACS undetected galaxies. We analyse the dependence of the SF activity, stellar mass and specific SFR on the group-centric distance, up to z similar to 1.6, for the first time. We do not find any correlation between the mean SFR and group-centric distance at any redshift. We do not observe any strong mass segregation either, in agreement with predictions from simulations. Our results suggest that either groups have a much smaller spread in accretion times with respect to the clusters and that the relaxation time is longer than the group crossing time.

In the local Universe, galaxy properties show a strong dependence on environment. In cluster cores, early-type galaxies dominate, whereas star-forming galaxies are more and more common in the outskirts. At higher redshifts and in somewhat less dense environments (e.g. galaxy groups), the situation is less clear. One open issue is that of whether and how the star formation rate (SFR) of galaxies in groups depends on the distance from the centre of mass. To shed light on this topic, we have built a sample of X-ray selected galaxy groups at 0 < z < 1.6 in various blank fields [Extended Chandra Deep Field South (ECDFS), Cosmological Evolution Survey (COSMOS), Great Observatories Origin Deep Survey (GOODS)]. We use a sample of spectroscopically confirmed group members with stellar mass M-star > 10(10.3) M-circle dot in order to have a high spectroscopic completeness. As we use only spectroscopic redshifts, our results are not affected by uncertainties due to projection effects. We use several SFR indicators to link the star formation (SF) activity to the galaxy environment. Taking advantage of the extremely deep mid-infrared Spitzer MIPS and far-infrared Herschel(1) PACS observations, we have an accurate, broad-band measure of the SFR for the bulk of the star-forming galaxies. We use multi-wavelength Spectral Energy Distribution (SED) fitting techniques to estimate the stellar masses of all objects and the SFR of the MIPS and PACS undetected galaxies. We analyse the dependence of the SF activity, stellar mass and specific SFR on the group-centric distance, up to z similar to 1.6, for the first time. We do not find any correlation between the mean SFR and group-centric distance at any redshift. We do not observe any strong mass segregation either, in agreement with predictions from simulations. Our results suggest that either groups have a much smaller spread in accretion times with respect to the clusters and that the relaxation time is longer than the group crossing time.

In the local Universe, galaxy properties show a strong dependence on environment. In cluster cores, early-type galaxies dominate, whereas star-forming galaxies are more and more common in the outskirts. At higher redshifts and in somewhat less dense environments (e.g. galaxy groups), the situation is less clear. One open issue is that of whether and how the star formation rate (SFR) of galaxies in groups depends on the distance from the centre of mass. To shed light on this topic, we have built a sample of X-ray selected galaxy groups at 0 < z < 1.6 in various blank fields [Extended Chandra Deep Field South (ECDFS), Cosmological Evolution Survey (COSMOS), Great Observatories Origin Deep Survey (GOODS)]. We use a sample of spectroscopically confirmed group members with stellar mass M-star > 10(10.3) M-circle dot in order to have a high spectroscopic completeness. As we use only spectroscopic redshifts, our results are not affected by uncertainties due to projection effects. We use several SFR indicators to link the star formation (SF) activity to the galaxy environment. Taking advantage of the extremely deep mid-infrared Spitzer MIPS and far-infrared Herschel(1) PACS observations, we have an accurate, broad-band measure of the SFR for the bulk of the star-forming galaxies. We use multi-wavelength Spectral Energy Distribution (SED) fitting techniques to estimate the stellar masses of all objects and the SFR of the MIPS and PACS undetected galaxies. We analyse the dependence of the SF activity, stellar mass and specific SFR on the group-centric distance, up to z similar to 1.6, for the first time. We do not find any correlation between the mean SFR and group-centric distance at any redshift. We do not observe any strong mass segregation either, in agreement with predictions from simulations. Our results suggest that either groups have a much smaller spread in accretion times with respect to the clusters and that the relaxation time is longer than the group crossing time.

We investigate the evolution of the star formation rate (SFR)-density relation in the Extended Chandra Deep Field South and the Great Observatories Origin Deep Survey fields up to z similar to 1.6. In addition to the 'traditional method', in which the environment is defined according to a statistical measurement of the local galaxy density, we use a 'dynamical' approach, where galaxies are classified according to three different environment regimes: group, 'filament-like' and field. Both methods show no evidence of an SFR-density reversal. Moreover, group galaxies show a mean SFR lower than other environments up to z similar to 1, while at earlier epochs group and field galaxies exhibit consistent levels of star formation (SF) activity. We find that processes related to a massive dark matter halo must be dominant in the suppression of the SF below z similar to 1, with respect to purely density-related processes. We confirm this finding by studying the distribution of galaxies in different environments with respect to the so-called main sequence (MS) of star-forming galaxies. Galaxies in both group and 'filament-like' environments preferentially lie below the MS up to z similar to 1, with group galaxies exhibiting lower levels of star-forming activity at a given mass. At z > 1, the star-forming galaxies in groups reside on the MS. Groups exhibit the highest fraction of quiescent galaxies up to z similar to 1, after which group, 'filament-like' and field environments have a similar mix of galaxy types. We conclude that groups are the most efficient locus for SF quenching. Thus, a fundamental difference exists between bound and unbound objects, or between dark matter haloes of different masses.