Multi-Wavelength Facets of Galaxy Clusters

Cluster cosmology, as investigated by the number counts method, is deeply linked to the constituent properties of our Universe and small-scale astrophysical phenomena. In the number counts method, a key challenge is relating observations of cluster galaxy members or the gas component to the total mass of the system. This dissertation aims to address this challenge by developing a better understanding of mass--observables relation, with a subsequent goal of enhancing the interpretation of cluster samples that have emerged from large-scale multi-wavelength surveys. These surveys include the XMM-XXL project, the Local Cluster Substructure Survey (LoCuSS), and eventually the Dark Energy Survey data (DES). The results of this work support the science goal of understanding the content and evolution of the Universe's most massive systems, thereby improving cosmological constraints leading to a better understanding of the constituents of our Universe. In this dissertation, I propose a novel method for cluster mass estimation based on member galaxy kinematics. I demonstrate a percent-level accuracy for the expected conditional log-mass, which implies that this algorithm is one of the most accurate algorithms available in the literature. The accuracy of this algorithm is extensively evaluated on a set of large-scale simulations. Next, all key systematics are identified and calibrated. With this method, we then estimate dynamical masses of a large, optically-selected cluster sample derived from the Sloan Digital Sky Survey (SDSS) and an X-ray-selected cluster sample derived from the XXL Survey. The multi-wavelength scaling behavior of cluster observables is driven by the astrophysical evolution of the baryonic components within the potential well of massive halos. To facilitate the multi-wavelength scaling modeling, I study the stellar and gas content of dark matter halos extracted from the BAHAMAS simulations, a set of large-scale, full-physics hydrodynamical simulations. The results verify the popular log-normal model of the halo population, but deviate from the power-law approximation. With these simulations, I establish a new set of predictions, most importantly an intrinsic anti-correlation between gas mass and stellar content of these systems. This anti-correlation is a key prediction that we continue to strive to confirm through a subset of the LoCuSS cluster sample. I implement a robust hierarchical Bayesian inference algorithm, which models the effects of sample selection and the measurement error covariance, to examine the gas and stellar contents of the underlying dark matter halos. To study the relation between the mass of dark matter halos and the multi-wavelength cluster observables, I apply this model to a subset of the LoCuSS cluster sample. Most importantly, this model enables us to examine the predicted anti-correlation between gas and stellar content of these systems. Finally, the results of this study establish the first empirical evidence for this anti-correlation, which has a profound implication for how the Universe's most massive structures formed and evolved.PHDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/145977/1/aryaf_1.pd

Gravitational Collapse, Chaos in CFT Correlators and the Information Paradox

We consider gravitational collapse of a massless scalar field in asymptotically Anti de Sitter spacetime. Following the AdS/CFT dictionary we further study correlations in the field theory side by way of the Klein-Gordon equation of a probe scalar field in the collapsing background. We present evidence that in a certain regime the probe scalar field behaves chaotically, thus supporting Hawking's argument in the black hole information paradox proposing that although the information can be retrieved in principle, deterministic chaos impairs, in practice, the process of unitary extraction of information from a black hole. We emphasize that quantum chaos will change this picture.Comment: 5 pages, 3 figure

A Model for Multi-property Galaxy Cluster Statistics

The massive dark matter halos that host groups and clusters of galaxies have observable properties that appear to be log-normally distributed about power-law mean scaling relations in halo mass. Coupling this assumption with either quadratic or cubic approximations to the mass function in log space, we derive closed-form expressions for the space density of halos as a function of multiple observables as well as forms for the low-order moments of properties of observable-selected samples. Using a Tinker mass function in a {\Lambda}CDM cosmology, we show that the cubic analytic model reproduces results obtained from direct, numerical convolution at the 10 percent level or better over nearly the full range of observables covered by current observations and for redshifts extending to z = 1.5. The model provides an efficient framework for estimating effects arising from selection and covariance among observable properties in survey samples.Comment: 9 pages, 4 figures, uses on-line mass function calculator http://hmf.icrar.org/. Submitted to MNRA

ActiveRemediation: The Search for Lead Pipes in Flint, Michigan

We detail our ongoing work in Flint, Michigan to detect pipes made of lead and other hazardous metals. After elevated levels of lead were detected in residents' drinking water, followed by an increase in blood lead levels in area children, the state and federal governments directed over $125 million to replace water service lines, the pipes connecting each home to the water system. In the absence of accurate records, and with the high cost of determining buried pipe materials, we put forth a number of predictive and procedural tools to aid in the search and removal of lead infrastructure. Alongside these statistical and machine learning approaches, we describe our interactions with government officials in recommending homes for both inspection and replacement, with a focus on the statistical model that adapts to incoming information. Finally, in light of discussions about increased spending on infrastructure development by the federal government, we explore how our approach generalizes beyond Flint to other municipalities nationwide.Comment: 10 pages, 10 figures, To appear in KDD 2018, For associated promotional video, see https://www.youtube.com/watch?v=YbIn_axYu9

A Dirty Holographic Superconductor

We study the effects of disorder on a holographic superconductor by introducing a random chemical potential on the boundary. We consider various realizations of disorder and find that the critical temperature for superconductivity is enhanced. We also present evidence for a precise form of renormalization in this system. Namely, when the random chemical potential is characterized by a Fourier spectrum of the form $k^{-2\alpha}$ we find that the spectra of the condensate and the charge density are again power-laws, whose exponents are accurately and universally governed by linear functions of $\alpha$.Comment: 5 pages, 8 figures. v3: discussion improved, references added, typos corrected, results unchange

Galaxy Cluster Mass Estimation from Stacked Spectroscopic Analysis

We use simulated galaxy surveys to study: i) how galaxy membership in redMaPPer clusters maps to the underlying halo population, and ii) the accuracy of a mean dynamical cluster mass, $M_\sigma(\lambda)$, derived from stacked pairwise spectroscopy of clusters with richness $\lambda$. Using $\sim\! 130,000$ galaxy pairs patterned after the SDSS redMaPPer cluster sample study of Rozo et al. (2015 RMIV), we show that the pairwise velocity PDF of central--satellite pairs with $m_i < 19$ in the simulation matches the form seen in RMIV. Through joint membership matching, we deconstruct the main Gaussian velocity component into its halo contributions, finding that the top-ranked halo contributes $\sim 60\%$ of the stacked signal. The halo mass scale inferred by applying the virial scaling of Evrard et al. (2008) to the velocity normalization matches, to within a few percent, the log-mean halo mass derived through galaxy membership matching. We apply this approach, along with mis-centering and galaxy velocity bias corrections, to estimate the log-mean matched halo mass at $z=0.2$ of SDSS redMaPPer clusters. Employing the velocity bias constraints of Guo et al. (2015), we find $\langle \ln(M_{200c})|\lambda \rangle = \ln(M_{30}) + \alpha_m \ln(\lambda/30)$ with $M_{30} = 1.56 \pm 0.35 \times 10^{14} M_\odot$ and $\alpha_m = 1.31 \pm 0.06_{stat} \pm 0.13_{sys}$. Systematic uncertainty in the velocity bias of satellite galaxies overwhelmingly dominates the error budget.Comment: 14 pages, 7 figure

Holographic p-wave Superconductor with Disorder

We implement the effects of disorder on a holographic p-wave superconductor by introducing a random chemical potential which defines the local energy of the charge carriers. Since there are various possibilities for the orientation of the vector order parameter, we explore the behaviour of the condensate in the parallel and perpendicular directions to the introduced disorder. We clarify the nature of various branches representing competing solutions and construct the disordered phase diagram. We find that moderate disorder enhances superconductivity as determined by the value of the condensate. Though we mostly focus on uncorrelated noise, we also consider a disorder characterized by its spectral properties and study in detail its influence on the spectral properties of the condensate and charge density. We find fairly universal responses of the resulting power spectra characterized by linear functions of the disorder power spectrum.Fil: Arean, Daniel. Instituto Max Planck de Física; AlemaniaFil: Pando Zayas, Leopoldo. University of Michigan; Estados UnidosFil: Salazar, Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Scardicchio, Antonello. The Abdus Salam. International Centre for Theoretical Physics; Italia. Columbia University; Estados Unidos. Princeton University; Estados Unido