Complementary to the existing spectroscopy in the CNOC2 fields, the GEEC has built up a mul- tiwavelength dataset, including Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS), infrared (IR), and ultraviolet (UV) imaging as well as X-ray data (described and utilized in this thesis), in order to study galaxy groups in these fields in detail. Figures 2.1 and 2.2 show the two CNOC2 fields used in this thesis work (the RA14h and RA21h patches) with relevant coverage overlaid. In summary, we have the following data (with variable spatial completeness):
•the original CNOC2 UBVRI photometry and spectroscopy
•high resolution HST-ACS imaging
•deep Magellan-LDSS2, Magellan Inamori Magellan Areal Camera and Spectrograph (IMACS), & VLT-FORS2 spectroscopy
•New Technology Telescope Son of ISAAC (NTT-SOFI; Ks-band), CFHT Wide-field InfraRed Camera (WIRcam), & William Herschel Telescope (WHT) Isaac Newton Group Red Imaging Device (INGRID) near infrared imaging
•mid-infrared imaging from the Spitzer Space Telescope Multiband Imaging Photometer (MIPS) & Infrared Array Camera IRAC
•improved optical imaging with CFHT-MegaCam & CFH12K
•Galaxy Evolution Explorer (GALEX) UV imaging
Figure 2.1: Multiwavelength coverage of the CNOC2 RA14h field. Red x’s mark Carlberg et al. groups and pluses those groups subsequently targeted with LDSS2. Small blue squares show regions covered by ACS. Black rectangles show previously observed FORS2 spectroscopic regions. Pink and red squares indicate SOFI and INGRID near IR respectively, while large red and blue dashed show archival IRAC and MIPS mid-IR. The green rectangle outlines our deep CFH12K optical imaging and cyan rectangle the MegaCam coverage. The large blue circle shows GALEX UV coverage. Finally, black circles show the XMM and large blue squares the Chandra X-ray coverage areas which are the focus of this thesis.
Figure 2.2: Multiwavelength coverage of the CNOC2 RA21h field. Symbols are the same as in Fig. 2.1.
Using this dataset, GEEC optical systems have now been extensively explored. Prior to the start of this thesis, several papers had already been published. Wilman began the in-depth study (and expansion, see §2.1) of the Carlberg et al. groups and found trends in the fraction of passive galaxies consistent with the differences between group and field galaxies seen in the local universe (Wilman et al., 2005a) and evidence that the star formation history in groups is influenced by their environment (Wilman et al., 2005b). The stellar mass of these systems was presented in Balogh et al. (2007) and no significant evidence for environment-driven evolution in group stellar mass from z∼0.4 to today found.
After the initiation of this thesis work, study of the optically-selected GEEC groups contin- ued. Using an IRAC color to identify passive galaxies in a stellar mass selected sample of the GEEC groups, Wilman et al. (2008) found a deficit in the fraction of infrared-excess galaxies at fixed group stellar mass in groups, relative to the field. Quantitative morphologies of the GEEC systems were compared to those of a low redshift sample of groups (drawn from the Millennium Galaxy Catalogue) with both showing a deficit of disc-dominated galaxies with respect to the field (McGee et al., 2008). Wilman et al. (2009) presented the HST-based visually classified morphologies of group galaxies, finding that groups contain significantly higher fractions of S0 galaxies than the field at fixed luminosity, with a similar fraction to that found in z∼0.4 clus- ters, and suggesting that interaction with a bright X-ray emitting IGM is not important for the formation of these objects.
Balogh et al. (2009) detailed the photometric analysis of the GEEC fields, which combined optical CHF12K and Megacam observations with near IR data. The resulting photometric cata- logs have been utilized in this thesis work. Galaxy colors and star formation for 98 of the GEEC groups were also presented, confirming the earlier conclusions that star formation is not signifi- cantly enhanced in the group environment and that current galaxy formation models overpredict quenching. A study of ten of the GEEC groups extending membership to fainter magnitudes con- ducted by Henderson (2010) found little evidence for strong evolution of the luminosity function in groups with redshift and a tendency of the faint galaxies in groups to be blue (e.g. a strong trend of decreasing red fraction toward fainter magnitudes). The star formation properties of the GEEC systems were further explored by McGee et al. (2011) and supplemented with those of lower redshift (z∼0.08) groups from the Sloan Digital Sky Survey (SDSS). Though the fraction of passive galaxies was found to be higher in groups than the field, the star formation properties of star-forming galaxies were similar in both environments. MIPS 24 micron observations were also used to study star formation in the GEEC groups by Tyler et al. (2011) and member galax- ies were found to lie between field and cluster galaxies in terms of mass, morphology, and star formation rates. Hou et al. (2009, 2012) characterized dynamical complexity and substructure in the most massive GEEC systems, finding evidence that groups containing significant sub- structure have global properties and galaxy populations differing from those of groups without detected substructure but no sign of star-formation quenching in galaxies residing in regions of substructure. Currently, the GEEC sample is being extended to higher redshifts and preliminary results, including evidence for a significant population of galaxies with intermediate colors (be- tween blue, star forming spiral galaxies and red, ‘dead’ galaxies which are primarily early types), have been presented in Balogh et al. (2011b).