We use a cosmological numerical simulation to study the tidal features produced by a minor merger with an elliptical galaxy. We find that the simulated tidal features are quantitatively similar to the red tidal features, i.e., dry tidal features, recently found in deep images of elliptical galaxies at intermediate redshifts. The minor merger in our simulation does not trigger star formation due to active galactic nuclei heating. Therefore, both the tidal features and the host galaxy are red, i.e., a dry minor merger. The stellar mass of the infalling satellite galaxy is about 10(10) M-circle dot, and the tidal debris reach the surface brightness of mu(R) similar to 27 mag arcsec(-2). Thus, we conclude that tidal debris from minor mergers can explain the observed dry tidal features in elliptical galaxies at intermediate redshifts, although other mechanisms (such as major dry mergers) may also be important.

We use a cosmological numerical simulation to study the tidal features produced by a minor merger with an elliptical galaxy. We find that the simulated tidal features are quantitatively similar to the red tidal features, i.e., dry tidal features, recently found in deep images of elliptical galaxies at intermediate redshifts. The minor merger in our simulation does not trigger star formation due to active galactic nuclei heating. Therefore, both the tidal features and the host galaxy are red, i.e., a dry minor merger. The stellar mass of the infalling satellite galaxy is about 10(10) M-circle dot, and the tidal debris reach the surface brightness of mu(R) similar to 27 mag arcsec(-2). Thus, we conclude that tidal debris from minor mergers can explain the observed dry tidal features in elliptical galaxies at intermediate redshifts, although other mechanisms (such as major dry mergers) may also be important.

We have undertaken a multiwavelength project to study the relatively unknown properties of groups and poor clusters of galaxies at intermediate redshifts. In this paper, we describe the XMM-Newton observations of six X-ray selected groups with 0.2 < z < 0: 6. The X-ray properties of these systems are generally in good agreement with the properties of low-redshift groups. They appear to follow the scaling relations between luminosity, temperature, and velocity dispersion defined by low-redshift groups and clusters. The X-ray emission in four of the six groups is also centered on a dominant early-type galaxy. The lack of a bright elliptical galaxy at the peak of the group X-ray emission is rare at low redshifts, and the other two groups may be less dynamically evolved. We find indications of excess entropy in these systems over self-similar predictions out to large radii. We also confirm the presence of at least one X-ray-luminous AGN associated with a group member galaxy and find several other potential group AGNs.

We have undertaken a multiwavelength project to study the relatively unknown properties of groups and poor clusters of galaxies at intermediate redshifts. In this paper, we describe the XMM-Newton observations of six X-ray selected groups with 0.2 < z < 0: 6. The X-ray properties of these systems are generally in good agreement with the properties of low-redshift groups. They appear to follow the scaling relations between luminosity, temperature, and velocity dispersion defined by low-redshift groups and clusters. The X-ray emission in four of the six groups is also centered on a dominant early-type galaxy. The lack of a bright elliptical galaxy at the peak of the group X-ray emission is rare at low redshifts, and the other two groups may be less dynamically evolved. We find indications of excess entropy in these systems over self-similar predictions out to large radii. We also confirm the presence of at least one X-ray-luminous AGN associated with a group member galaxy and find several other potential group AGNs.

We have undertaken a multiwavelength project to study the relatively unknown properties of groups and poor clusters of galaxies at intermediate redshifts. In this paper, we describe the XMM-Newton observations of six X-ray selected groups with 0.2 < z < 0: 6. The X-ray properties of these systems are generally in good agreement with the properties of low-redshift groups. They appear to follow the scaling relations between luminosity, temperature, and velocity dispersion defined by low-redshift groups and clusters. The X-ray emission in four of the six groups is also centered on a dominant early-type galaxy. The lack of a bright elliptical galaxy at the peak of the group X-ray emission is rare at low redshifts, and the other two groups may be less dynamically evolved. We find indications of excess entropy in these systems over self-similar predictions out to large radii. We also confirm the presence of at least one X-ray-luminous AGN associated with a group member galaxy and find several other potential group AGNs.

X-ray observations of hot, intergalactic gas in galaxy groups provide a useful means of characterizing the global properties of groups. However, X-ray studies of large group samples have typically involved very shallow X-ray exposures or have been based on rather heterogeneous samples. Here we present the first results of the XI (XMM/IMACS) Groups Project, a study targeting, for the first time, a redshift-selected, statistically unbiased sample of galaxy groups using deep X-ray data. Combining this with radio observations of cold gas and optical imaging and spectroscopy of the galaxy population, the project aims to advance the understanding of how the properties and dynamics of group galaxies relate to global group properties. Here, X-ray and optical data of the first four galaxy groups observed as part of the project are presented. In two of the groups we detect diffuse emission with a luminosity of L-X approximate to 10(41) erg s(-1), among the lowest found for any X-ray detected group thus far, with a comparable upper limit for the other two. Compared to typical X-ray selected groups of similar velocity dispersion, these four systems are all surprisingly X-ray faint. We discuss possible explanations for the lack of significant X-ray emission in the groups, concluding that these systems are most likely collapsing for the first time. Our results strongly suggest that, unlike our current optically selected sample, previous X-ray selected group samples represented a biased picture of the group population. This underlines the necessity of a study of this kind, if one is to reach an unbiased census of the properties of galaxy groups and the distribution of baryons in the Universe.

X-ray observations of hot, intergalactic gas in galaxy groups provide a useful means of characterizing the global properties of groups. However, X-ray studies of large group samples have typically involved very shallow X-ray exposures or have been based on rather heterogeneous samples. Here we present the first results of the XI (XMM/IMACS) Groups Project, a study targeting, for the first time, a redshift-selected, statistically unbiased sample of galaxy groups using deep X-ray data. Combining this with radio observations of cold gas and optical imaging and spectroscopy of the galaxy population, the project aims to advance the understanding of how the properties and dynamics of group galaxies relate to global group properties. Here, X-ray and optical data of the first four galaxy groups observed as part of the project are presented. In two of the groups we detect diffuse emission with a luminosity of L-X approximate to 10(41) erg s(-1), among the lowest found for any X-ray detected group thus far, with a comparable upper limit for the other two. Compared to typical X-ray selected groups of similar velocity dispersion, these four systems are all surprisingly X-ray faint. We discuss possible explanations for the lack of significant X-ray emission in the groups, concluding that these systems are most likely collapsing for the first time. Our results strongly suggest that, unlike our current optically selected sample, previous X-ray selected group samples represented a biased picture of the group population. This underlines the necessity of a study of this kind, if one is to reach an unbiased census of the properties of galaxy groups and the distribution of baryons in the Universe.

X-ray observations of hot, intergalactic gas in galaxy groups provide a useful means of characterizing the global properties of groups. However, X-ray studies of large group samples have typically involved very shallow X-ray exposures or have been based on rather heterogeneous samples. Here we present the first results of the XI (XMM/IMACS) Groups Project, a study targeting, for the first time, a redshift-selected, statistically unbiased sample of galaxy groups using deep X-ray data. Combining this with radio observations of cold gas and optical imaging and spectroscopy of the galaxy population, the project aims to advance the understanding of how the properties and dynamics of group galaxies relate to global group properties. Here, X-ray and optical data of the first four galaxy groups observed as part of the project are presented. In two of the groups we detect diffuse emission with a luminosity of L-X approximate to 10(41) erg s(-1), among the lowest found for any X-ray detected group thus far, with a comparable upper limit for the other two. Compared to typical X-ray selected groups of similar velocity dispersion, these four systems are all surprisingly X-ray faint. We discuss possible explanations for the lack of significant X-ray emission in the groups, concluding that these systems are most likely collapsing for the first time. Our results strongly suggest that, unlike our current optically selected sample, previous X-ray selected group samples represented a biased picture of the group population. This underlines the necessity of a study of this kind, if one is to reach an unbiased census of the properties of galaxy groups and the distribution of baryons in the Universe.

As groups today contain similar to 60% of the galaxy population [1], and are the first step in the hierarchical growth tree which dominates structure formation, these environments must have a critical influence on the evolution of star formation in the Universe as a whole. Indeed their dynamics make them the ideal environments to foster galaxy galaxy interactions and mergers, leading to a dramatic transformation of galaxy properties. To study the evolution of galaxies in groups requires highly complete, targetted, deep spectroscopic surveys. At intermediate redshift, the only such is our sample of 26 groups at 0.3 < z < 0.55, selected from the CNOC2 redshift survey [2], with additional targetted spectroscopy using the Magellan 6.5m and VLT telescopes providing a complete kinematic description to a depth of similar to M-*. + 3 at z = 0.4. [3]. Our full multiwavelength dataset will include HST-ACS, GALEX UV. Chandra, XMM and Spitzer imaging, with the power to ultimately reveal the importance of the group environment in controlling the evolutionary fate of a galaxy. In this contribution, we present some of the more recent and illuminating analysis, revealing evolution in the group environment and the dependence of starformation and galaxy morphologies upon environment and stellar mass. Finally we discuss the important role Spitzer will play in revealing the processes actively transforming galaxies in the group environment.

As groups today contain similar to 60% of the galaxy population [1], and are the first step in the hierarchical growth tree which dominates structure formation, these environments must have a critical influence on the evolution of star formation in the Universe as a whole. Indeed their dynamics make them the ideal environments to foster galaxy galaxy interactions and mergers, leading to a dramatic transformation of galaxy properties. To study the evolution of galaxies in groups requires highly complete, targetted, deep spectroscopic surveys. At intermediate redshift, the only such is our sample of 26 groups at 0.3 < z < 0.55, selected from the CNOC2 redshift survey [2], with additional targetted spectroscopy using the Magellan 6.5m and VLT telescopes providing a complete kinematic description to a depth of similar to M-*. + 3 at z = 0.4. [3]. Our full multiwavelength dataset will include HST-ACS, GALEX UV. Chandra, XMM and Spitzer imaging, with the power to ultimately reveal the importance of the group environment in controlling the evolutionary fate of a galaxy. In this contribution, we present some of the more recent and illuminating analysis, revealing evolution in the group environment and the dependence of starformation and galaxy morphologies upon environment and stellar mass. Finally we discuss the important role Spitzer will play in revealing the processes actively transforming galaxies in the group environment.