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.

We present the data release of the Gemini-South GMOS spectroscopy in the fields of 11 galaxy groups at 0.8 < z < 1, within the COSMOS field. This forms the basis of the Galaxy Environment Evolution Collaboration 2 (GEEC2) project to study galaxy evolution in haloes with M similar to 10(13)M circle dot across cosmic time. The final sample includes 162 spectroscopically confirmed members with R < 24.75, and is >50 per cent complete for galaxies within the virial radius, and with stellar mass M-star > 10(10.3) M circle dot. Including galaxies with photometric redshifts, we have an effective sample size of similar to 400 galaxies within the virial radii of these groups. We present group velocity dispersions, dynamical and stellar masses. Combining with the GCLASS sample of more massive clusters at the same redshift, we find the total stellar mass is strongly correlated with the dynamical mass, with log M-200 = 1.20(logM(star) - 12) + 14.07. This stellar fraction of similar to 1 per cent is lower than predicted by some halo occupation distribution models, though the weak dependence on halo mass is in good agreement. Most groups have an easily identifiable most massive galaxy (MMG) near the centre of the galaxy distribution, and we present the spectroscopic properties and surface brightness fits to these galaxies. The total stellar mass distribution in the groups, excluding the MMG, compares well with an NFW (Navarro Frenk & White) profile with concentration 4, for galaxies beyond similar to 0.2R(200). This is more concentrated than the number density distribution, demonstrating that there is some mass segregation.

Fast radio bursts (FRBs) are one of the most tantalizing mysteries of the radio sky; their progenitors and origins remain unknown and until now no rapid multiwavelength follow-up of an FRB has been possible. New instrumentation has decreased the time between observation and discovery from years to seconds, and enables polarimetry to be performed on FRBs for the first time. We have discovered an FRB (FRB 140514) in real-time on 2014 May 14 at 17:14:11.06 UTC at the Parkes radio telescope and triggered follow-up at other wavelengths within hours of the event. FRB 140514 was found with a dispersion measure (DM) of 562.7(6) cm(-3) pc, giving an upper limit on source redshift of z less than or similar to 0.5. FRB 140514 was found to be 21 +/- 7 per cent (3 sigma) circularly polarized on the leading edge with a 1 sigma upper limit on linear polarization <10 per cent. We conclude that this polarization is intrinsic to the FRB. If there was any intrinsic linear polarization, as might be expected from coherent emission, then it may have been depolarized by Faraday rotation caused by passing through strong magnetic fields and/or high-density environments. FRB 140514 was discovered during a campaign to re-observe known FRB fields, and lies close to a previous discovery, FRB 110220; based on the difference in DMs of these bursts and time-on-sky arguments, we attribute the proximity to sampling bias and conclude that they are distinct objects. Follow-up conducted by 12 telescopes observing from X-ray to radio wavelengths was unable to identify a variable multiwavelength counterpart, allowing us to rule out models in which FRBs originate from nearby (z < 0.3) supernovae and long duration gamma-ray bursts.

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.

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.

Using data from four deep fields (COSMOS, AEGIS, ECDFS, and CDFN), we study the correlation between the position of galaxies in the star formation rate (SFR) versus stellar mass plane and local environment at z < 1.1. To accurately estimate the galaxy SFR, we use the deepest available Spitzer/MIPS 24 and Herschel/PACS data sets. We distinguish group environments (M-halo similar to 10(12.5-14.2)M(circle dot)) based on the available deep X-ray data and lower halo mass environments based on the local galaxy density. We confirm that the main sequence (MS) of star-forming galaxies is not a linear relation and there is a flattening towards higher stellar masses (M-* > 10(10.4-10.6) M-circle dot), across all environments. At high redshift (0.5 < z < 1.1), the MS varies little with environment. At low redshift (0.15 < z < 0.5), group galaxies tend to deviate from the mean MS towards the region of quiescence with respect to isolated galaxies and less-dense environments. We find that the flattening of the MS towards low SFR is due to an increased fraction of bulge-dominated galaxies at high masses. Instead, the deviation of group galaxies from the MS at low redshift is caused by a large fraction of red disc-dominated galaxies which are not present in the lower density environments. Our results suggest that above a mass threshold (similar to 10(10.4)-10(10.6) M-circle dot) stellar mass, morphology and environment act together in driving the evolution of the star formation activity towards lower level. The presence of a dominating bulge and the associated quenching processes are already in place beyond z similar to 1. The environmental effects appear, instead, at lower redshifts and have a long time-scale.