We present the global group properties of two samples of galaxy groups containing 39 high-quality X-ray-selected systems and 38 optically (spectroscopically) selected systems in coincident spatial regions at 0.12 < z < 0.79. The total mass range of the combined sample is similar to(10(12)-5) x 10(14) M-circle dot. Only nine optical systems are associable with X-ray systems. We discuss the confusion inherent in the matching of both galaxies to extended X-ray emission and of X-ray emission to already identified optical systems. Extensive spectroscopy has been obtained and the resultant redshift catalog and group membership are provided here. X-ray, dynamical, and total stellar masses of the groups are also derived and presented. We explore the effects of utilizing different centers and applying three different kinds of radial cut to our systems: a constant cut of 1 Mpc and two r(200) cuts, one based on the velocity dispersion of the system and the other on the X-ray emission. We find that an X-ray-based r(200) results in less scatter in scaling relations and less dynamical complexity as evidenced by results of the Anderson-Darling and Dressler-Schectman tests, indicating that this radius tends to isolate the virialized part of the system. The constant and velocity dispersion based cuts can overestimate membership and can work to inflate velocity dispersion and dynamical and stellar mass. We find L-X-sigma and M-stellar-L-X scaling relations for X-ray and optically selected systems are not dissimilar. The mean fraction of mass found in stars, excluding intracluster light, for our systems is similar to 0.014 with a logarithmic standard deviation of 0.398 dex. We also define and investigate a sample of groups which are X-ray underluminous given the total group stellar mass. For these systems the fraction of stellar mass contributed by the most massive galaxy is typically lower than that found for the total population of groups implying that there may be less intragroup medium contributed from the most massive member in these systems. Eighty percent of 15 underluminous groups have less than 40% of their stellar mass in the most massive galaxy which happens in less than 1% of cases with samples matched in stellar mass, taken from the combined group catalog.

We report the discovery of an X-ray group of galaxies located at a high redshift of z = 1.61 in the Chandra Deep Field South. Based on 4 Ms Chandra data, the group is first identified as an extended X-ray source. We have used a wealth of deep multi-wavelength data to identify the optical counterpart-our red sequence finder detects a significant over-density of galaxies at z similar to 1.6. The brightest group galaxy is spectroscopically confirmed at z = 1.61, based on published spectroscopic redshifts. Using this as a central redshift of the group, we measure an X-ray luminosity of L0.1-2.4keV = (1.8 +/- 0.6) x 10(43) erg s(-1), which then translates into a group mass of (3.2 +/- 0.8) x 10(13) M-circle dot. This is the lowest-mass group ever confirmed at z > 1.5. Deep optical-nearIR images from CANDELS reveal that the group exhibits a surprisingly prominent red sequence, and most of the galaxies are consistent with a formation redshift of z(f) = 3. A detailed analysis of the spectral energy distributions of the group member candidates confirms that most of them are indeed passive galaxies. Furthermore, their structural parameters measured from near-IR CANDELS images show that they are morphologically early-type. The newly identified group at z = 1.61 is dominated by quiescent early-type galaxies, and the group appears to be similar to those in the local Universe. One possible difference is the high fraction of AGN-38(-20)(+23)% of the bright group member candidates are AGN, which might indicate a role for AGN in the quenching of star formation. However, a statistical sample of high-z groups is needed to draw a general picture of groups at this redshift. Such a sample will hopefully be available in near-future surveys.

We present deep Gemini Multi-Object Spectrograph-South spectroscopy for 11 galaxy groups at 0.8 < z < 1.0, for galaxies with r(AB) < 24.75. Our sample is highly complete (> 66 per cent) for eight of the 11 groups. Using an optical-near-infrared colour-colour diagram, the galaxies in the sample were separated with a dust insensitive method into three categories: passive (red), star-forming (blue) and intermediate (green). The strongest environmental dependence is observed in the fraction of passive galaxies, which make up only similar to 20 per cent of the field in the mass range 10(10.3) < M-star/M-circle dot < 10(11.0), but are the dominant component of groups. If we assume that the properties of the field are similar to those of the 'pre-accreted' population, the environment quenching efficiency (is an element of(rho)) is defined as the fraction of field galaxies required to be quenched in order to match the observed red fraction inside groups. The efficiency obtained is similar to 0.4, similar to its value in intermediate-density environments locally. While green (intermediate) galaxies represent similar to 20 per cent of the star-forming population in both the group and field, at all stellar masses, the average specific star formation rate of the group population is lower by a factor of similar to 3. The green population does not show strong H delta absorption that is characteristic of starburst galaxies. Finally, the high fraction of passive galaxies in groups, when combined with satellite accretion models, require that most accreted galaxies have been affected by their environment. Thus, any delay between accretion and the onset of truncation of star formation (tau) must be <= 2 Gyr, shorter than the 3-7 Gyr required to fit data at z = 0. The relatively small fraction of intermediate galaxies require that the actual quenching process occurs quickly, with an exponential decay time-scale of tau(q) <= 1Gyr.

We report the discovery of the optical afterglow of the gamma-ray burst (GRB) 130702A, identified upon searching 71 deg(2) surrounding the Fermi Gamma-ray Burst Monitor (GBM) localization. Discovered and characterized by the intermediate Palomar Transient Factory, iPTF13bxl is the first afterglow discovered solely based on a GBM localization. Real-time image subtraction, machine learning, human vetting, and rapid response multi-wavelength follow-up enabled us to quickly narrow a list of 27,004 optical transient candidates to a single afterglow-like source. Detection of a new, fading X-ray source by Swift and a radio counterpart by CARMA and the Very Large Array confirmed the association between iPTF13bxl and GRB 130702A. Spectroscopy with the Magellan and Palomar 200 inch telescopes showed the afterglow to be at a redshift of z = 0.145, placing GRB 130702A among the lowest redshift GRBs detected to date. The prompt gamma-ray energy release and afterglow luminosity are intermediate between typical cosmological GRBs and nearby sub-luminous events such as GRB 980425 and GRB 060218. The bright afterglow and emerging supernova offer an opportunity for extensive panchromatic follow-up. Our discovery of iPTF13bxl demonstrates the first observational proof-of-principle for similar to 10 Fermi-iPTF localizations annually. Furthermore, it represents an important step toward overcoming the challenges inherent in uncovering faint optical counterparts to comparably localized gravitational wave events in the Advanced LIGO and Virgo era.

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.

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.

We present new analysis from the Group Environment Evolution Collaboration 2 (GEEC2) spectroscopic survey of galaxy groups at 0.8 < z < 1. Our previous work revealed an intermediate population between the star-forming and quiescent sequences and a strong environmental dependence in the fraction of quiescent galaxies. Only similar to 5 per cent of star-forming galaxies in both the group and field sample show a significant enhancement in star formation, which suggests that quenching is the primary process in the transition from the star-forming to the quiescent state. To model the environmental quenching scenario, we have tested the use of different exponential quenching time-scales and delays between satellite accretion and the onset of quenching. We find that with no delay, the quenching time-scale needs to be long in order to match the observed quiescent fraction, but then this model produces too many intermediate galaxies. Fixing a delay time of 3 Gyr, as suggested from the local Universe, produces too few quiescent galaxies. The observed fractions are best matched with a model that includes a delay that is proportional to the dynamical time and a rapid quenching time-scale (similar to 0.25 Gyr), but this model also predicts intermediate galaxies H delta strength higher than that observed. Using stellar synthesis models, we have tested other scenarios, such as the rejuvenation of star formation in early-type galaxies and a portion of quenched galaxies possessing residual star formation. If environment quenching plays a role in the GEEC2 sample, then our work suggests that only a fraction of intermediate galaxies may be undergoing this transition and that quenching occurs quite rapidly in satellite galaxies (less than or similar to 0.25 Gyr).

We report the discovery of a transparent sightline at projected distances of less than or similar to 20 kpc to an interacting pair of mature galaxies at z = 0.12. The sightline of the UV-bright quasar PG 1522+101 at z(em) = 1.328 passes at = 11.5 kpc from the higher mass galaxy (M-* = 10(10.6) M-circle dot) and = 20.4 kpc from the lower mass one (M-* = 10(10.0) M-circle dot). The two galaxies are separated by 9 kpc in projected distance and 30 km s(-1) in line-of-sight velocity. Deep optical images reveal tidal features indicative of close interactions. Despite the small projected distances, the quasar sightline shows little absorption associated with the galaxy pair with a total H i column density no greater than log N(HI)/cm(-2) = 13.65. This limiting H i column density is already two orders of magnitude less than what is expected from previous halo gas studies. In addition, we detect no heavy-element absorption features associated with the galaxy pair with 3 sigma limits of log N(Mg II)/cm(-2) < 12.2 and log N(OVI)/cm(-2) < 13.37. The probability of seeing such little absorption in a sightline passing at a small projected distance from two non-interacting galaxies is 0.2 per cent. The absence of strong absorbers near the close galaxy pair suggests that the cool gas reservoirs of the galaxies have been significantly depleted by the galaxy interaction. These observations therefore underscore the potential impact of galaxy interactions on the gaseous haloes around galaxies.