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Carnegie Mellon University MELLON COLLEGE of SCIENCE Carnegie Mellon University MELLON COLLEGE OF SCIENCE THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN THE FIELD OF PHYSICS TITLE: "Galaxy Clusters in the Presence of Substructure." PRESENTED BY: Evan Tucker ACCEPTED BY THE DEPARTMENT OF PHYSICS Matthew Walker 5/20/19 MATTHEW WALKER, CHAIR PROFESSOR DATE Scott Dodelson 5/23/19 SCOTT DODELSON, DEPT HEAD DATE APPROVED BY THE COLLEGE COUNCIL Rebecca Doerge 5/23/19 REBECCA DOERGE, DEAN DATE Galaxy Clusters in the Presence of Substructure by Evan Tucker Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Carnegie Mellon University Department of Physics Pittsburgh, Pennsylvania Advised by Professor Matthew G. Walker May 17, 2019 Abstract My thesis focused on developing an end-to-end program for dynamical analyses of galaxy clusters. The main interest of the thesis is to develop a dynamical mass estimator used for galaxy clusters that has the capability to account for substructure which is currently a limitation on most dynamical mass estimators. Through already established collaborations, I had access to a cutting-edge multi-object spectrograph, the Michigan/Magellan Fiber System (M2FS), on the 6.5m Clay-Magellan Telescope in Chile; therefore, a signifiant portion of my thesis involved the collection, data reduction, and spectral analysis of new galaxy spectra. As part of this collaboration, I became a core member of the M2FS observation team, which sent me to Chile about a half dozen times to aid in the observations with M2FS. The early portions of my thesis project focused on the handling of newly obtained galaxy spectra with M2FS. The first M2FS observations of galaxies within clusters were collected in November 2013 as a pilot program for testing this instruments ca- pabilities at observing unresolved stellar populations. My goal with this portion of the project was to familiarize myself with the M2FS instrument and it's observations as well as to learn how to reduce the collected data. As part of this familiarization, I learned first-hand how to observe with M2FS and aid in the collection of other ob- servations over a variety of scientific interests. While reducing my own observations, I developed a front-end GUI to simplify the data reduction process and help expedite the reduction of future observations. Although, the data reduction pipeline I devel- oped works well at reducing a subset of M2FS observations, I was unable generalize the pipeline fully to handle all M2FS configurations. This is due to variations be- tween configurations such as resolution settings, multi-order spectra, and wavelength coverages. I also helped in the collection of spectra with M2FS over a range of scientific purposes. For projects more related to my own work, I collected spectra for galaxies within the clusters Abell 1689, MACS0429, and CL 1301. MACS0429 was part of my own research project and so I detail in this thesis the targeting, observation, data reduction, and spectral fits. In a first published paper, we report the results of a pilot program to use the Mag- ellan/M2FS spectrograph to survey the galactic populations and internal kinematics of galaxy clusters. For this initial study, we present spectroscopic measurements for 223 quiescent galaxies observed along the line of sight to the galaxy cluster Abell 267 (z 0:23). We develop a Bayesian method for modeling the integrated light from each∼ galaxy as a simple stellar population, with free parameters that spec- ify redshift (vlos=c) and characteristic age, metallicity ([Fe=H]), alpha-abundance ([α=Fe]), and internal velocity dispersion (σint) for individual galaxies. Parameter estimates derived from our 1.5-hour observation of A267 have median random errors 1 of σvlos = 20 km s− , σAge = 1:2 Gyr, σ[Fe=H] = 0:11 dex, σ[α/Fe] = 0:07 dex, and 1 σσint = 20 km s− . In a second paper currently under review, we develop and implement a model to analyze the internal kinematics of galaxy clusters that may contain subpopula- tions of galaxies that do not independently trace the cluster potential. The model allows for substructures within the cluster environment, disentangles cluster mem- bers from contaminating foreground and background galaxies, and includes an over- all cluster rotation term as part of the cluster kinematics. We estimate the cluster velocity dispersion and/or mass while marginalizing over uncertainties in all of the above complexities. We use these results to explore the sensitivity of inferred cluster properties to the treatment of substructure. Compared to a model that assumes no substructure, our substructure model reduces the dynamical mass of A267 by 22% 1 ∼ and shifts the cluster mean velocity by 100 km s− , approximately doubling the offset with respect to the velocity of A267's∼ brightest cluster galaxy. Embedding the spherical Jeans equation within this framework, we infer for A267 a halo of mass 14 M200 = 7:0 1:3 10 M =h and concentration log10 c200 = 0:71 0:38, consistent with the mass-concentration± × relation found in cosmological simulations.± A third paper (in preparation) presents the results of new M2FS spectroscopy for the cluster MACS0429. This cluster is part of the Cluster Lensing and Supernova Survey with Hubble (CLASH) and was the only CLASH cluster observable in the southern sky not covered by the spectroscopic follow-up program CLASH-VLT. We obtained over 700 spectra of 300 unique galaxies along with a couple dozen strongly lensed background galaxies.∼ We fit these spectra using the population synthesis pre- viously model applied to Abell 267 thus obtaining parameter estimates describing the mean redshift, age, metallicity, chemical enrichment and velocity dispersion of each galaxy's stellar population. 2 Acknowledgments I'd like to thank all the graduate students, post-docs and professors that helped me reach this pinnacle. Mario, for helping with observations and data reduction; you've taught me so much about the technical side of observational astronomy and instrumentation. Ed, for sharing in your expertise, life experiences, and helping to pass the time while observing in Chile. My committee, Rachel, Sergey, Hy, and Peter, for listening to my progression, showing patience as I learned, reading this thesis, and guiding my throughout this whole process. And of course, I'd like to thank my wonderful advisor Matt. You provided a nurturing environment that truly helped me grow as a researcher. I cannot thank you enough for your support and guidance. Lastly and most importantly, I'd like to dedicate this entire thesis to my life partner and best friend Alexandra. Without your unwavering dedication and support these past six years, I would have never been able to accomplish as much as I did. Everything that we achieve going forward is directly tied to the support you provided during the hardest years of my life. You are my rock, my protection, my everything. I love you. Contents 1 Introduction 1 1.1 Galaxy Clusters as Cosmological Probes . .3 1.1.1 Current Cosmological Models . .3 1.1.2 The Halo Mass Function . .7 1.2 Mass Estimation Techniques for Galaxy Clusters . .8 1.2.1 Lensing Masses . .9 1.2.2 X-ray Masses . 10 1.2.3 Dynamical Masses . 10 1.2.4 Current Limits on Galaxy Cluster Mass Estimates . 14 1.3 Previous Substructure Analysis Techniques . 15 1.4 Summary of Thesis . 16 2 Multi-object Spectroscopic Observations 18 2.1 The Michigan/Magellan Fiber System . 19 2.2 Observations with M2FS . 19 2.3 Data Reduction . 24 2.4 Observations of Galaxy Clusters with M2FS . 32 3 Magellan/M2FS Spectroscopy of Galaxy Clusters: Stellar Popula- tion Model and Application to Abell 267 35 3.1 Introduction . 35 3.2 Observations and Data Reduction . 37 3.2.1 Target Selection . 37 3.2.2 Observations . 37 3.2.3 Data Reduction . 38 3.2.4 Sky Subtraction . 41 3.3 Integrated Light Population Synthesis Model For Galaxy Spectra . 41 3.3.1 Integrated Light Spectral Library . 42 3.3.2 Spectral Model . 44 3.4 Analysis of Spectra . 46 3.4.1 Likelihood function and free parameters . 47 3.4.2 Parameter Estimation . 47 ii 3.4.3 Tests with Mock Spectra . 51 3.4.4 External Tests . 52 3.5 Results for Abell 267 . 55 3.5.1 Comparison to previous redshift results . 59 3.6 Conclusions . 61 4 Magellan/M2FS Spectroscopy of MACS 0429: Observations and Spectral Fits 63 4.1 Introduction . 63 4.2 Observations . 64 4.2.1 Target Selection . 64 4.2.2 M2FS Spectroscopy . 65 4.3 Spectral Fits . 68 4.3.1 Line Spread Function . 68 4.3.2 M0429 Spectral Fits . 69 4.3.3 Comparison of repeat observations . 72 4.4 Conclusions . 73 5 Galaxy Cluster Mass Estimates in the Presence of Substructure 75 5.1 Introduction . 75 5.2 Galaxy Cluster Mixture Model . 77 5.3 Tests with Mock Observations from Simulations . 80 5.3.1 The MultiDark Simulation . 80 5.3.2 Mock Observations . 80 5.3.3 Model Setup . 81 5.3.4 Results . 84 5.4 Application to A267 . 90 5.4.1 Observational Dataset . 90 5.4.2 Contamination Model . 91 5.4.3 Uniform Velocity Dispersion Profile . 94 5.4.4 Dark Matter Halo Model . 103 5.5 Conclusions . 114 6 Conclusions and Future Outlook 118 A Data Tables 124 iii List of Tables 1.1 Current cosmological parameter estimates for flat-ΛCDM cosmology. These values come from a joint analysis of DES Y1 + Planck + JLA + BAO [51]. In ΛCDM the equation of state of dark energy is fixed at w = 1. Included here is the parameter estimate for w to show that even− when this assumption is not made, the value is still close to 1 .7 − 3.1 Free parameters and priors for Integrated Light Population Synthesis Model .
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