Subhabrata Majumdar

Cosmological Constraints from the Red-Sequence Cluster Survey

We present a first cosmological analysis of a refined cluster catalog from the Red-Sequence Cluster Survey (RCS). The input cluster sample is derived from the deepest 72.07 deg2 of the RCS images, which probe to the highest redshift and lowest mass limits. The catalog contains 956 clusters over 0.35 < z < 0.95, limited by cluster richness and richness error. The calibration of the survey images has been extensively cross-checked against publicly available Sloan Digital Sky Survey imaging, and the cluster redshifts and richness that result from this well-calibrated subset of data are robust. We analyze the cluster sample via a general self-calibration technique. We fit simultaneously for the matter density, Ωm, the normalization of the power spectrum, σ8, and four parameters describing the calibration of cluster richness to mass, its evolution with redshift, and scatter in the mass-richness relation. The principal goal of this general analysis is to establish the consistency (or lack thereof) between the fitted parameters (both cosmological and cluster mass observables) and available results on both from independent measures. From an unconstrained analysis, the derived values of Ωm and σ8 are 0.31 and 0.67, respectively. An analysis including Gaussian priors on the slope and zero point of the mass-richness relation gives very similar results: 0.30 and 0.70. Both analyses are in acceptable agreement with the current literature. The derived parameters describing the mass-richness relation in the unconstrained fit are also eminently reasonable and in good agreement with existing follow-up data on both the RCS-1 and other cluster samples. Our results directly demonstrate that future surveys (optical and otherwise), with much larger samples of clusters, can give constraints competitive with other probes of cosmology.

SPECTROSCOPIC CONFIRMATION OF TWO MASSIVE RED-SEQUENCE-SELECTED GALAXY CLUSTERS AT z ∼ 1.2 IN THE SpARCS-NORTH CLUSTER SURVEY

The Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) is a z ′ -passband imaging survey, consisting of deep (z ′ ≃ 24 AB) observations made from both hemispheres using the CFHT 3.6m and CTIO 4m telescopes. The survey was designed with the primary aim of detecting galaxy clusters at z > 1. In tandem with pre-existing 3.6µm observations from the Spitzer Space Telescope SWIRE Legacy Survey, SpARCS detects clusters using an infrared adaptation of the two-filter redsequence cluster technique. The total effective area of the SpARCS cluster survey is 41.9 deg 2 . In this paper, we provide an overview of the 13.6 deg 2 Southern CTIO/MOSAICII observations. The 28.3 deg 2 Northern CFHT/MegaCam observations are summarized in a companion paper by Muzzin et al. (2008a). In this paper, we also report spectroscopic confirmation of SpARCS J003550431224, a very rich galaxy cluster at z = 1.335, discovered in the ELAIS-S1 field. To date, this is the highest spectroscopically confirmed redshift for a galaxy cluster discovered using the red-sequence technique. Based on nine confirmed members, SpARCS J003550-431224 has a preliminary velocity dispersion of 1050 ±230 km s −1 . With its proven capability for efficient cluster detection,SpARCS is a demonstration that we have entered an era of large, homogeneously-selected z > 1 cluster surveys. Subject headings: surveys — cosmology: observations — galaxies: clusters: general — galaxies: highredshift — infrared: galaxies

Secondary anisotropies of the CMB

The Cosmic Microwave Background fluctuations provide a powerful probe of the dark ages of the universe through the imprint of the secondary anisotropies associated with the reionization of the universe and the growth of structure. We review the relation between the secondary anisotropies and the primary anisotropies that are directly generated by quantum fluctuations in the very early universe. The physics of secondary fluctuations is described, with emphasis on the ionization history and the evolution of structure. We discuss the different signatures arising from the secondary effects in terms of their induced temperature fluctuations, polarization and statistics. The secondary anisotropies are being actively pursued at present, and we review the future and current observational status.

Post-Planck Dark Energy Constraints

We constrain plausible dark energy models, parametrized by multiple candidate equation of state, using the recently published Cosmic Microwave Background (CMB) temperature anisotropy data from Planck together with the WMAP-9 low-

Probing the Evolution of the Gas Mass Fraction with the Sunyaev-Zeldovich Effect

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On Cooling Flows and the Sunyaev-Zeldovich Effect

polarization data and data from low redshift surveys. To circumvent the limitations of any particular equation of state towards describing all existing dark energy models, we work with three different equation of state covering a broader class of dark energy models and, hence, provide more robust and generic constraints on the dark energy properties. We show that a clear tension exists between dark energy constraints from CMB and non-CMB observations when one allows for dark energy models having both phantom and non-phantom behavior; while CMB is more favorable to phantom models, the low-z data prefers model with behavior close to a Cosmological Constant. Further, we reconstruct the equation of state of dark energy as a function of redshift using the results from combined CMB and non-CMB data and find that Cosmological Constant lies outside the 1

Energy Deposition Profiles and Entropy in Galaxy Clusters

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Using clusters in Sunyaev-Zel'dovich effect plus x-ray surveys as an ensemble of rulers to constrain cosmology

band for multiple dark energy models allowing phantom behavior. A considerable fine tuning is needed to keep models with strict non-phantom history inside 2

Searching for systematics in SNIa and galaxy cluster data using the cosmic duality relation

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Constraints on structure formation models from the sunyaev- zel'dovich effect

allowed range. This result might motivate one to construct phantom models of dark energy,which is achievable in the presence of higher derivative operators as in string theory. However, disallowing phantom behavior, based only on strong theoretical prior, leads to both CMB and non-CMB datasets agree on the nature of dark energy, with the mean equation of state being very close to the Cosmological Constant. Finally, to illustrate the impact of additional dark energy parameters on other cosmological parameters, we provide the cosmological parameter constraints for different dark energy models.