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The Galaxy Environment of Quasars in the Clowes-Campusano Large Quasar Group

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The Galaxy Environment of Quasars in the Clowes-Campusano Large Quasar Group The Galaxy Environment of Quasars in the Clowes-Campusano Large Quasar Group Christopher Paul Haines A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy. Centre for Astrophysics Department of Physics, Astronomy and Mathematics University of Central Lancashire June 2001 Declaration The work presented in this thesis was carried out in the Department of Physics, Astromony and Mathematics, University of Central Lancashire. Unless otherwise stated it is the original work of the author. While registered for the degree of Doctor of Philosophy, the author has not been a registered candidate for another award of the University. This thesis has not been submitted in whole, or in part, for any other degree. Christopher Haines June 2001 Abstract Quasars have been used as efficient probes of high-redshift galaxy clustering as they are known to favour overdense environments. Quasars may also trace the large- scale structure of the early universe (0.4 1< z 1< 2) in the form of Large Quasar Groups (LQGs), which have comparable sizes (r.J 100-200hMpc) to the largest structures seen at the present epoch. This thesis describes an ultra-deep, wide-field optical study of a region containing three quasars from the largest known LJQG, the Clowes-Campusano LQG of at least 18 quasars at z 1.3, to examine their galaxy environments and to find indications of any associated large-scale structure in the form of galaxies. The optical data were obtained using the Big Throughput Camera (BTC) on the 4-m Blanco telescope at the Cerro Tololo Interamerican Observatory (CTIO) over two nights in April 1998, resulting in ultra-deep V, I imaging of a 40.6 x 34.9 arcmin 2 field centred at l0L47m30s, +05 0 30'00" containing three quasars from the LQG as well as four quasars at higher redshifts. The final catalogues contain 10 sources and are 50% complete to V 26.35 and I 25.85 in the fully exposed areas. The Cluster Red Sequence method of Gladders & Yee (2000) is used to identify and characterise galaxy clusters in the BTC field. The method is motivated by the observation that the bulk of early-type galaxies in all rich clusters lie along a tight, linear colour-magnitude relation - the cluster red sequence - which evolves with redshift, allowing the cluster redshift to be estimated from the colour of the red sequence. The method is applied to the detection of high-redshift clusters in the BTC field through the selection of galaxies redder than the expected colour of the z = 0.5 red sequence. A 2c excess of these red galaxies is found in the BTC field in comparison to the 27arcmin 2 ETS-DEEP HDF-South field. These galaxies are shown from the EIS-DEEP UBVRIJHK 3 photometry to he early-type galaxies at 0.7 1< z 1.5. This excess, corresponding to 1000 extra red galaxies over the BTC field, along with the 3c excess of Mgti absorbers observed at 1.2 < z < 1.3 (Williger et al., 2000), supports the hypothesis that the Clowes-Campusano LQG traces a large-scale structure in the form of galaxies at z 1.3. Four high-redshift cluster candidates are found, one of which is confirmed by additional K data to be at z = 0.8 + 0.1. Two of the high-redshift clusters are associated with quasars: the z = 1.426 quasar is located on the periphery of a cluster of V - I 3 galaxies; and the z = 1.226 LQC quasar is found within a large-scale structure of 100-150 red galaxies extending over 2-3h'Mpc. Additional K imaging confirms their association with the quasar, with red sequences at V - K 6.9 and I - K 4.3 indicating a population of 15-18 massive ellipticals at z = 1.2 ± 0.1 that are concentrated in two groups on either side of the quasar. The four z ± 1.3 quasars in the BTC field are found in a wide variety of en- vironments, from those indistinguishable from the field, to being associated with rich clusters, but are on average in overdense regions comparable to poor clusters. These results are similar to those of previous studies of quasars at these redshifts, and are consistent with the quasars being hosted by massive ellipticals which trace mass in the same biased manner. It is also notable how the quasars associated with clustering are located on the cluster peripheries rather than in the high-density cluster cores, a result which is initially surprising given that quasars are thought to be hosted by massive elliptical galaxies, but in retrospect can be understood in the framework of both galaxy interaction and galaxy formation quasar triggering mechanisms. Contents 1 Introduction 1 1.1 Overview of the Thesis .......................... 1 1.2 The Standard Cosmological Model ................... 2 1.3 Statistical Descriptors of Clustering ................... 5 1.4 Structure Formation and Evolution ................... 7 1.5 Large Scale Structure at Low Redshifts ................. 11 1.6 Quasars - A Summary ......................... 14 1.7 The Galaxy Environments of Quasars .................. 18 1.8 Quasar Clustering ............................. 21 1.9 Large Quasar Groups ........................... 25 1.9.1 The Webster LQG at z 0.37 .................. 25 1.9.2 The Crampton et al. LQG at z 1.1 ............... 26 1.9.3 The Clowes-Campusano LQG at z 1.3 ............ 31 1.9.4 Other Large Quasar Groups ................... 32 2 Ultra-deep Imaging of the Clowes-Campusano Large Quasar Group 35 2.1 Introduction ................................ 35 2.2 BTC Observations ............................ 37 2.3 Reduction of the BTC Images ...................... 41 2.3.1 Summary ............................. 41 2.3.2 Initial Reduction Steps ...................... 42 2.3.3 Distortion modelling and removal ................ 46 2.3.4 Photometric Calibration ..................... 54 2.3.5 Producing the Final Images ................... 58 2.3.6 Astrometric Calibration ..................... 58 2.3.7 Production of a False Colour Image ............... 63 2.4 Source Extraction - Producing the Final Catalogue ......... 64 2.4.1 Extraction ............................. 64 2.4.2 Photometry ............................ 65 2.4.3 Background Modelling and Weight Maps ............ 68 2.4.4 Star - Galaxy Separation ..................... 72 2.4.5 Source Parameters Output to the Final Catalogue ....... 76 2.5 Sources in the BTC images ........................ 78 2.5.1 Magnitude Limits ......................... 78 2.5.2 Galaxy Counts .......................... 84 2.6 Summary ................................. 89 3 Analysis of Galaxy Clustering in the I3TC Images 90 3.1 Introduction ................................ 90 3.2 The Cluster Red Sequence Method ................... 91 3.2.1 The Red Sequence in Nearby Clusters .............. 92 3.2.2 Evolution of the Cluster Red Sequence ............. 97 3.2.3 Motivation for using the Cluster Red Sequence Method . 100 3.2.4 Basic Implementation of the Cluster Red Sequence method to Identify Clusters ......................... 103 3.3 Cluster Analysis Methods ........................ 103 3.3.1 Parametric Methods ....................... 104 3.3.2 A non-parametric approach to cluster analysis ......... 104 3.3.3 Estimating the probability density function ........... 105 3.3.4 Cluster Identification and Analysis ............... 108 3.3.5 Estimating the Significance of Substructure .......... 113 3.4 Applying the CRS Method to the BTC Images ............. 115 3.4.1 Definition of the Redshift Slices ................. 115 3.4.2 Estimating the Galaxy Surface Density ............. 116 3.5 Example Clusters from the Redshift Slices ............... 124 3.6 Summary ................................. 128 ii 4 The Identification of Galaxy Clustering Associated with the Clowes-Campusano Large Quasar Group 129 4.1 Introduction ................................ 129 4.2 High Redshift Galaxies in the BTC images ............... 130 4.3 Comparison with the EIS-DEEP HDF-South Field .......... 135 4.4 Clustering of the Red Galaxies ...................... 148 4.5 Spatial Distribution of the Red Galaxies ................ 152 4.6 Galaxy Clustering Around Density Maxima #70 and #71 ...... 158 4.7 The Galaxy Environment of the z = 1.426 Quasar ........... 162 4.8 The Galaxy Environment of the z = 1.230 LQG Quasar ........ 169 4.9 The Galaxy Environment of the z = 1.306 LQG Quasar ........ 169 4.10 The Galaxy Environment of the z = 1.226 LQG Quasar ........ 172 4.11 Comparison with Previous Studies .................... 176 4.12 Consequences for the Evolution of Galaxy Clusters .......... 180 4.13 The Galaxy Environments of z 1.3 Quasars ............. 185 4.14 Evidence for a Large-Scale Structure at z 1.3 ............ 188 4.15 Summary ................................. 189 5 The Galaxy Environment of the z = 1.226 LQG Quasar 191 5.1 Introduction ................................ 191 5.2 Observations ................................ 193 5.3 Results - Galaxy Counts ........................ 197 5.4 Galaxy Colours .............................. 203 5.5 Photometric Redshift Estimation .................... 206 5.5.1 Red Sequence Galaxies ...................... 214 5.5.2 Red Outlier Galaxies ....................... 216 5.6 Spatial Distribution olGalaxies ..................... 217 5.6.1 Red Sequence Galaxies ...................... 217 5.6.2 Clustering across Large-Scales ................... 23 5.6.3 Blue Galaxies ........................... 225 5.7 The Immediate Environment of the Quasar ............... 226 5.8 Discussion and Conclusions ........................ 28 'II 5.8.1 A Possible Cluster Merging Event ................230 5.8.2 Comparison with Other Work ..................231
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