We compare deep Magellan spectroscopy of 26 groups at 0.3 <= z <= 0.55, selected from the Canadian Network for Observational Cosmology 2 field survey, with a large sample of nearby groups from the 2PIGG catalogue. We find that the fraction of group galaxies with significant [O II]lambda 3727 emission (>= 5 angstrom) increases strongly with redshift, from similar to 29 per cent in 2dFGRS to 58 per cent in CNOC2, for all galaxies brighter than similar to M-* + 1.75. This trend is parallel to the evolution of field galaxies, where the equivalent fraction of emission-line galaxies increases from similar to 53 to similar to 75 per cent. The fraction of emission-line galaxies in groups is lower than in the field, across the full redshift range, indicating that the history of star formation in groups is influenced by their environment. We show that the evolution required to explain the data is inconsistent with a quiescent model of galaxy evolution; instead, discrete events in which galaxies cease forming stars (truncation events) are required. We constrain the probability of truncation (P-trunc) and find that a high value is required in a simple evolutionary scenario neglecting galaxy mergers (P-trunc greater than or similar to 0.3 Gyr(-1)). However, without assuming significant density evolution, P-trunc is not required to be larger in groups than in the field, suggesting that the environmental dependence of star formation was embedded at redshifts z greater than or similar to 0.45.

The evolution of galaxies in groups may have important implications for the evolution of the star formation history of the Universe, since many processes which operate in groups may suppress star formation and the fraction of galaxies in bound groups grows rapidly between z = 1 and the present day. In this paper, we present an investigation of the properties of galaxies in galaxy groups at intermediate redshift (z similar to 0.4). The groups were selected from the Canadian Network for Observational Cosmology Redshift Survey (CNOC2) redshift survey as described by Carlberg et al., with further spectroscopic follow-up undertaken at the Magellan telescope in order to improve the completeness and depth of the sample. We present the data for the individual groups, and find no clear trend in the fraction of passive galaxies with group velocity dispersion and group concentration. We stack the galaxy groups in order to compare the properties of group galaxies with those of field galaxies at the same redshift. The groups contain a larger fraction of passive galaxies than the field, this trend being particularly clear for galaxies brighter than M-BJ < -20 in the higher velocity dispersion groups. In addition, we see evidence for an excess of bright passive galaxies in the groups relative to the field. In contrast, the luminosity functions of the star-forming galaxies in the groups and the field are consistent. These trends are qualitatively consistent with the differences between group and field galaxies seen in the local Universe.

The evolution of galaxies in groups may have important implications for the evolution of the star formation history of the Universe, since many processes which operate in groups may suppress star formation and the fraction of galaxies in bound groups grows rapidly between z = 1 and the present day. In this paper, we present an investigation of the properties of galaxies in galaxy groups at intermediate redshift (z similar to 0.4). The groups were selected from the Canadian Network for Observational Cosmology Redshift Survey (CNOC2) redshift survey as described by Carlberg et al., with further spectroscopic follow-up undertaken at the Magellan telescope in order to improve the completeness and depth of the sample. We present the data for the individual groups, and find no clear trend in the fraction of passive galaxies with group velocity dispersion and group concentration. We stack the galaxy groups in order to compare the properties of group galaxies with those of field galaxies at the same redshift. The groups contain a larger fraction of passive galaxies than the field, this trend being particularly clear for galaxies brighter than M-BJ < -20 in the higher velocity dispersion groups. In addition, we see evidence for an excess of bright passive galaxies in the groups relative to the field. In contrast, the luminosity functions of the star-forming galaxies in the groups and the field are consistent. These trends are qualitatively consistent with the differences between group and field galaxies seen in the local Universe.

The evolution of galaxies in groups may have important implications for the evolution of the star formation history of the Universe, since many processes which operate in groups may suppress star formation and the fraction of galaxies in bound groups grows rapidly between z = 1 and the present day. In this paper, we present an investigation of the properties of galaxies in galaxy groups at intermediate redshift (z similar to 0.4). The groups were selected from the Canadian Network for Observational Cosmology Redshift Survey (CNOC2) redshift survey as described by Carlberg et al., with further spectroscopic follow-up undertaken at the Magellan telescope in order to improve the completeness and depth of the sample. We present the data for the individual groups, and find no clear trend in the fraction of passive galaxies with group velocity dispersion and group concentration. We stack the galaxy groups in order to compare the properties of group galaxies with those of field galaxies at the same redshift. The groups contain a larger fraction of passive galaxies than the field, this trend being particularly clear for galaxies brighter than M-BJ < -20 in the higher velocity dispersion groups. In addition, we see evidence for an excess of bright passive galaxies in the groups relative to the field. In contrast, the luminosity functions of the star-forming galaxies in the groups and the field are consistent. These trends are qualitatively consistent with the differences between group and field galaxies seen in the local Universe.

The evolution of galaxies in groups may have important implications for the evolution of the star formation history of the Universe, since many processes which operate in groups may suppress star formation and the fraction of galaxies in bound groups grows rapidly between z = 1 and the present day. In this paper, we present an investigation of the properties of galaxies in galaxy groups at intermediate redshift (z similar to 0.4). The groups were selected from the Canadian Network for Observational Cosmology Redshift Survey (CNOC2) redshift survey as described by Carlberg et al., with further spectroscopic follow-up undertaken at the Magellan telescope in order to improve the completeness and depth of the sample. We present the data for the individual groups, and find no clear trend in the fraction of passive galaxies with group velocity dispersion and group concentration. We stack the galaxy groups in order to compare the properties of group galaxies with those of field galaxies at the same redshift. The groups contain a larger fraction of passive galaxies than the field, this trend being particularly clear for galaxies brighter than M-BJ < -20 in the higher velocity dispersion groups. In addition, we see evidence for an excess of bright passive galaxies in the groups relative to the field. In contrast, the luminosity functions of the star-forming galaxies in the groups and the field are consistent. These trends are qualitatively consistent with the differences between group and field galaxies seen in the local Universe.

We have analyzed Hubble Space Telescope spectroscopy of 24 nearby active galactic nuclei (AGNs) to investigate spatially resolved gas kinematics in the narrow-line region ( NLR). These observations effectively isolate the nuclear line profiles on less than 100 pc scales and are used to investigate the origin of the substantial scatter between the widths of strong NLR lines and the stellar velocity dispersion sigma* of the host galaxy, a quantity that relates with substantially less scatter to the mass of the central, supermassive black hole and more generally characterize variations in the NLR velocity field with radius. We find that line widths measured with STIS at a range of spatial scales systematically underestimate both sigma(*) and the line width measured from ground- based observations, although they do have comparably large scatter to the relation between ground- based NLR line width and sigma(*). There are no obvious trends in the residuals when compared with a range of host galaxy and nuclear properties. The widths and asymmetries of [O III] lambda 5007 and [S II] lambda lambda 6716, 6731 as a function of radius exhibit a wide range of behavior. Some of the most common phenomena are substantial width increases from the STIS to the large- scale, ground- based aperture and almost no change in line profile between the unresolved nuclear spectrum and ground-based measurements. We identify asymmetries in a surprisingly large fraction of low-ionization [S II] line profiles and several examples of substantial red asymmetries in both [O III] and [S II]. These results underscore the complexity of the circumnuclear material that constitutes the NLR and suggest that the scatter in the NLR width and sigma(*) correlation cannot be substantially reduced with a simple set of empirical relations.

We have analyzed Hubble Space Telescope spectroscopy of 24 nearby active galactic nuclei (AGNs) to investigate spatially resolved gas kinematics in the narrow-line region ( NLR). These observations effectively isolate the nuclear line profiles on less than 100 pc scales and are used to investigate the origin of the substantial scatter between the widths of strong NLR lines and the stellar velocity dispersion sigma* of the host galaxy, a quantity that relates with substantially less scatter to the mass of the central, supermassive black hole and more generally characterize variations in the NLR velocity field with radius. We find that line widths measured with STIS at a range of spatial scales systematically underestimate both sigma(*) and the line width measured from ground- based observations, although they do have comparably large scatter to the relation between ground- based NLR line width and sigma(*). There are no obvious trends in the residuals when compared with a range of host galaxy and nuclear properties. The widths and asymmetries of [O III] lambda 5007 and [S II] lambda lambda 6716, 6731 as a function of radius exhibit a wide range of behavior. Some of the most common phenomena are substantial width increases from the STIS to the large- scale, ground- based aperture and almost no change in line profile between the unresolved nuclear spectrum and ground-based measurements. We identify asymmetries in a surprisingly large fraction of low-ionization [S II] line profiles and several examples of substantial red asymmetries in both [O III] and [S II]. These results underscore the complexity of the circumnuclear material that constitutes the NLR and suggest that the scatter in the NLR width and sigma(*) correlation cannot be substantially reduced with a simple set of empirical relations.

We have analyzed Hubble Space Telescope spectroscopy of 24 nearby active galactic nuclei (AGNs) to investigate spatially resolved gas kinematics in the narrow-line region ( NLR). These observations effectively isolate the nuclear line profiles on less than 100 pc scales and are used to investigate the origin of the substantial scatter between the widths of strong NLR lines and the stellar velocity dispersion sigma* of the host galaxy, a quantity that relates with substantially less scatter to the mass of the central, supermassive black hole and more generally characterize variations in the NLR velocity field with radius. We find that line widths measured with STIS at a range of spatial scales systematically underestimate both sigma(*) and the line width measured from ground- based observations, although they do have comparably large scatter to the relation between ground- based NLR line width and sigma(*). There are no obvious trends in the residuals when compared with a range of host galaxy and nuclear properties. The widths and asymmetries of [O III] lambda 5007 and [S II] lambda lambda 6716, 6731 as a function of radius exhibit a wide range of behavior. Some of the most common phenomena are substantial width increases from the STIS to the large- scale, ground- based aperture and almost no change in line profile between the unresolved nuclear spectrum and ground-based measurements. We identify asymmetries in a surprisingly large fraction of low-ionization [S II] line profiles and several examples of substantial red asymmetries in both [O III] and [S II]. These results underscore the complexity of the circumnuclear material that constitutes the NLR and suggest that the scatter in the NLR width and sigma(*) correlation cannot be substantially reduced with a simple set of empirical relations.

We present a galaxy survey of the field surrounding PKS 0405 - 123 performed with the WFCCD spectrometer at Las Campanas Observatory. The survey is comprised of two data sets: ( 1) a greater than 95% complete survey to R = 20 mag of the field centered on PKS 0405 - 123 with 10' radius (L approximate to 0.1L(*) and radius of 1 Mpc at z = 0.1); and (2) a set of four discontiguous ( i.e., nonoverlapping), flanking fields covering approximate to 1 deg(2) area with completeness approximate to 90% to R = 19.5 mag. With these data sets, one can examine the local and large-scale galactic environment of the absorption systems identified toward PKS 0405 - 123. In this paper, we focus on the O vi systems analyzed in Paper I. The results suggest that this gas arises in a diverse set of galactic environments including the halos of individual galaxies, galaxy groups, filamentary-like structures, and also regions devoid of luminous galaxies. In this small sample, there are no obvious trends between galactic environment and the physical properties of the gas. Furthermore, we find similar results for a set of absorption systems with comparable N-H I but no detectable metal lines. The observations indicate that metals are distributed throughout a wide range of environments in the local universe. Future papers in this series will address the distribution of galactic environments associated with metal-line systems and the Ly alpha forest based on data for over 10 additional fields. All of the data presented in this paper are made public at a dedicated web site.

We present a galaxy survey of the field surrounding PKS 0405 - 123 performed with the WFCCD spectrometer at Las Campanas Observatory. The survey is comprised of two data sets: ( 1) a greater than 95% complete survey to R = 20 mag of the field centered on PKS 0405 - 123 with 10' radius (L approximate to 0.1L(*) and radius of 1 Mpc at z = 0.1); and (2) a set of four discontiguous ( i.e., nonoverlapping), flanking fields covering approximate to 1 deg(2) area with completeness approximate to 90% to R = 19.5 mag. With these data sets, one can examine the local and large-scale galactic environment of the absorption systems identified toward PKS 0405 - 123. In this paper, we focus on the O vi systems analyzed in Paper I. The results suggest that this gas arises in a diverse set of galactic environments including the halos of individual galaxies, galaxy groups, filamentary-like structures, and also regions devoid of luminous galaxies. In this small sample, there are no obvious trends between galactic environment and the physical properties of the gas. Furthermore, we find similar results for a set of absorption systems with comparable N-H I but no detectable metal lines. The observations indicate that metals are distributed throughout a wide range of environments in the local universe. Future papers in this series will address the distribution of galactic environments associated with metal-line systems and the Ly alpha forest based on data for over 10 additional fields. All of the data presented in this paper are made public at a dedicated web site.