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 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 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 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 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 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 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.

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.