MULTI-WAVELENGTH STRONG LENSING STUDY of LOW REDSHIFT CLUSTER CORES By
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MULTI-WAVELENGTH STRONG LENSING STUDY OF LOW REDSHIFT CLUSTER CORES by PAUL EDWARD MAY A thesis submitted to The University of Birmingham for the degree of DOCTOR OF PHILOSOPHY Astrophysics and Space Research Group School of Physics & Astronomy The University of Birmingham Sept 2012 Abstract This thesis covers initial work to increase the total number of galaxy clusters with strong lensing features and, therefore, lensing derived masses. These clusters also possess other multi-wavelength measurements that can be, and were, used for comparison. The work included an investigation into what additional information Dressler Shectman analysis of the incomplete redshift cluster member galaxy samples produced as a result of prioritising mask slit placement on potential strong lensing images. With the test blind on areas centred around the BCG, only a qualitative link was found, providing possible assistance with mass model parametisation. From the sample of eight clusters reduced, five had strong lensing features, of which, A 3084 had an unusual and rare lensing configuration. Analysis of A 3084 with relatively shallow survey data revealed a cluster with the largest cluster-scale halo centred on the intra-cluster gas and not the BCG: these two were offset from one another. The BCG had a compact DM halo coincident with it, yielding a high substructure fraction of fsub= 0.73 0.13 which, along with smooth X-ray surface brightness contours, bi-modal cluster ± galaxy redshift histogram and luminosity map, provided evidence that the interpretation of the cluster had suffered a cluster-cluster merger. From the redshift reduction, five new strong lensing models were produced following similar methods to the ones used for A 3084. With the addition of a cluster from Paraficz et al. (2012), this increased the initial sample size from 17 to 23, providing a 35% in- ∼ crease, with all clusters having other multi-wavelength measurements. Following previous SL literature comparisons a fit of M2D (R < 250 kpc) against TX was carried out, but large scatter was observed in this. A possible link was found between the residuals of the fit with that of the clusters’ BCG ellipticity after a cut was made of m12 1 for luminosity ≥ gap to remove potentially disturbed clusters. To my Mother and Father. ACKNOWLEDGEMENTS I would like to gratefully acknowledge the help of my fellow PhD students Tim James and Victoria Hamilton-Morris for their help and company while learning the ropes. I would also like to thank the members of the Extragalactic Research Group at Birmingham and the members of the LoCuSS collaboration for their help over the years, with additional thanks to David Stops for his assistance with computing matters. I would also like to thank my parents, friends and family for their help and support all through the years. Finally thanking my supervisor, Graham Smith for his support and guidance through my PhD whilst I have been at Birmingham. STATEMENT OF ORIGINALITY Both chapters 1 & 2 are based on existing work and literature and are not my own work. Reduction of HST, colour catalogues and J and K band luminosity maps (in chapter 4) were carried out by Victoria Hamilton-Morris and the X-ray reduction and analysis by Alaistair Sanderson. In chapter 3, collaboration with faint lensed object spectrum extraction and inter- pretation was provided by Johan Richard (with A 2537 & A 368 redshifts used in strong lensing model constraints derived from his work) and by Graham Smith. In chapter 5, model selection and interpretation was aided by insights from Johan Richard and Gra- ham Smith. The multiple image positions from Johan Richard for A 2537 were used in my strong lens models. Chapter 4 is based upon a paper that I have under preparation for publication, with the current list of co-authors listed at the beginning of that chapter. The chapter has also benefited from feedback from and discussion with the co-authors (as well as local astronomers). All redshifts (apart from those already mentioned) and Dressler Shectman statistics were reduced and derived by myself. All strong lensing models and their derived values and analysis were also produced by myself. This was my own work, under the supervision of Graham Smith and with aid provided by relevant colleagues in the LoCuSS collaboration and the Extragalactic Research Group based at the University of Birmingham Physics & Astronomy Department. Section 2.2.1 uses equations and information from the book titled ’Gravitational § Lensing: Strong, Weak and Micro’ by Schneider, P., Kochanek, C. and Wambsganss, J. (Meylan et al., 2006). The basic equations and workings in section 2.4 & 2.4.1 were taken from “Data § § Analysis A Bayesian Tutorial” by D. S. Sivia. The basic equations and workings in this section 2.4.2 are based on “Bayesian Logical § Data Analysis for the Physical Sciences” by Phil Gregory (Gregory, 2005). Any non-original work is referenced. This work has not been previously submitted for a degree. CONTENTS 1 Introduction 1 1.1 DarkMatter................................... 3 1.2 Λ-CDMCosmology............................... 7 1.3 GalaxyClusters................................. 10 1.4 ClusterObservables-Global. 15 1.4.1 Optical.................................. 15 1.4.2 X-ray .................................. 18 1.4.3 Millimetre................................ 20 1.5 ClusterObservables-Structural . 22 1.5.1 Optical.................................. 22 1.5.2 X-ray .................................. 24 1.5.3 Millimetre................................ 25 1.6 Gravitationallensing . 25 1.6.1 Microlensing............................... 26 1.6.2 WeakLensing.............................. 27 1.6.3 A Short History of Gravitational Lensing by Galaxy Clusters.... 28 1.6.4 ClusterLensing ............................. 40 1.7 LoCuSS ..................................... 42 1.8 ThesisOverview................................. 43 2 Theory 46 2.1 LensingTheory ................................. 46 2.2 StrongLensing ................................. 47 2.2.1 LensEquations ............................. 47 2.2.2 Magnification and Distortion . 55 2.2.3 ImageNumbers............................. 56 2.2.4 Critical Curves and Caustics . 57 2.2.5 Image Classification . 57 2.3 MassSheetDegeneracy............................. 59 2.4 BayesianTheory ................................ 60 2.4.1 ModelSelection............................. 61 2.4.2 Markov Chain Monte Carlo . 62 2.4.3 LensTool................................. 66 2.5 DensityProfilesofHalos ............................ 69 2.5.1 NFWMassModel ........................... 69 2.5.2 PIEMDMassModel .......................... 72 3 Optical Spectroscopy 74 3.1 SpectroscopicObservations. 75 3.1.1 ReductionMethod ........................... 75 3.1.2 GMOS.................................. 76 3.1.3 FORS2.................................. 79 3.1.4 Observations .............................. 80 3.2 RedshiftHistograms .............................. 82 3.2.1 ReflexAdditions ............................ 84 3.2.2 Velocity dispersion vs TX−ray ..................... 86 3.3 DresslerShectman ............................... 88 3.3.1 DSStatistics .............................. 89 3.4 DresslerShectmanAnalysis . 91 3.5 Comparative Observations - HST &X-ray .................. 92 3.6 DataSummary ................................. 93 3.7 Analysis&Interpretation . 94 3.7.1 Abell2813................................ 94 3.7.2 Abell2895................................ 95 3.7.3 Abell368 ................................ 95 3.7.4 Abell3084................................101 3.7.5 Abell3088................................105 3.7.6 Abell2537................................107 3.7.7 Abell3364................................107 3.7.8 RXCJ0528................................112 3.8 DynamicalComparisons . .114 3.8.1 EffectsofREFLEXadditions . .116 3.9 ChapterDiscussion ...............................118 3.10ChapterSummary ...............................121 4 Abell 3084 Strong Lensing Analysis 122 4.1 HyperbolicUmbilicCatastrophe. 122 4.2 ObservationsandAnalysis . .124 4.2.1 Hubble Space Telescope imaging ....................124 4.2.2 Ground-based near-infrared imaging . 126 4.2.3 Opticalspectroscopy . .129 4.2.4 Chandra X-rayobservations . .134 4.2.5 Summary ................................140 4.3 Strong-lensModelandResults. 141 4.3.1 ModelFitting ..............................143 4.3.2 TheMassandStructureoftheClusterCore . 149 4.4 SummaryandDiscussion. .153 4.4.1 MainResults ..............................153 4.4.2 PhysicalInterpretation . 155 4.5 Summary ....................................157 5 Strong Lensing Mass vs X-Ray Temperatures 159 5.1 StrongLensingModels .............................160 5.1.1 Abell2813................................160 5.1.2 Abell368 ................................162 5.1.3 Abell2895................................164 5.1.4 Abell2537................................167 5.1.5 Results..................................167 5.2 ExpandedSample................................167 5.3 DataSummary .................................170 5.4 Analysis .....................................170 5.4.1 MassObservables............................172 5.4.2 MassvsTemperature. .173 5.5 Residuals ....................................176 5.5.1 SubstructureFraction . .177 5.5.2 LuminosityGap.............................177 5.5.3 BCGEllipticity .............................178 5.6 ResidualDiscussion...............................180 5.7 ChapterDiscussion ...............................182 5.8 ChapterSummary ...............................183