A Parameterized Galaxy Catalog Simulator for Testing Cluster Finding, Mass Estimation, and Photometric Redshift Estimation in Optical and Near-infrared Surveys

We present a galaxy catalog simulator that converts N -body simulations with halo and subhalo catalogs into mock, multiband photometric catalogs. The simulator assigns galaxy properties to each subhalo in a way that reproduces the observed cluster galaxy halo occupation distribution, the radial and mass-dependent variation in fractions of blue galaxies, the luminosity functions in the cluster and the field, and the color-magnitude relation in clusters. Moreover, the evolution of these parameters is tuned to match existing observational constraints. Parameterizing an ensemble of cluster galaxy properties enables us to create mock catalogs with variations in those properties, which in turn allows us to quantify the sensitivity of cluster finding to current observational uncertainties in these properties. Field galaxies are sampled from existing multiband photometric surveys of similar depth. We present an application of the catalog simulator to characterize the selection function and contamination of a galaxy cluster finder that utilizes the cluster red sequence together with galaxy clustering on the sky. We estimate systematic uncertainties in the selection to be at the ≤15% level with current observational constraints on cluster galaxy populations and their evolution. We find the contamination in this cluster finder to be ~35% to redshift z ~ 0.6. In addition, we use the mock galaxy catalogs to test the optical mass indicator B gc and a red-sequence redshift estimator. We measure the intrinsic scatter of the B gc -mass relation to be approximately log normal with ##IMG## [http://ej.iop.org/images/0004-637X/747/1/58/apj417488ieqn1.gif] {\sigma _{\log _{10M\sim 0.25 and we demonstrate photometric redshift accuracies for massive clusters at the ~3% level out to z ~ 0.7.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98548/1/0004-637X_747_1_58.pd

Orientation bias of optically selected galaxy clusters and its impact on stacked weak-lensing analyses

Weak-lensing measurements of the averaged shear profiles of galaxy clusters binned by some proxy for cluster mass are commonly converted to cluster mass estimates under the assumption that these cluster stacks have spherical symmetry. In this paper, we test whether this assumption holds for optically selected clusters binned by estimated optical richness. Using mock catalogues created from N-body simulations populated realistically with galaxies, we ran a suite of optical cluster finders and estimated their optical richness. We binned galaxy clusters by true cluster mass and estimated optical richness and measure the ellipticity of these stacks. We find that the processes of optical cluster selection and richness estimation are biased, leading to stacked structures that are elongated along the line of sight. We show that weak-lensing alone cannot measure the size of this orientation bias. Weak-lensing masses of stacked optically selected clusters are overestimated by up to 3–6 per cent when clusters can be uniquely associated with haloes. This effect is large enough to lead to significant biases in the cosmological parameters derived from large surveys like the Dark Energy Survey, if not calibrated via simulations or fitted simultaneously. This bias probably also contributes to the observed discrepancy between the observed and predicted Sunyaev–Zel’dovich signal of optically selected clusters

Early Type Galaxies And Reliable Galaxy Cluster Selection

In an era of precision cosmology, clusters of galaxies are the natural consequences under the hierarchical scenario, within which clusters directly encapsulate the history of structure formation. Thus, determining the mass distribution of clusters as a function of redshift enables fundamental tests of this structure formation process. My projects have initially been motivated by an intellectual inquiry into how we can effectively and accurately analyze data from large cluster surveys, such as the South Pole Telescope (SPT), the Blanco Cosmology Survey (BCS) and the upcoming Dark Energy Survey (DES), which now extends to the galaxy formation and evolution studies. Through this thesis project followed by immediate extension of the thesis, I, therefore, aim to achieve three distinct, but highly inter-related main research goals: (1) creating mock catalogs that represent the universe well enough, (2) employing these mock catalogs to quantitatively characterize optical selection tools and then applying those well understood selection tools to large new surveys, and (3) exploring the underlying physics of galaxy population and property evolution over the cosmic time. Clusters of galaxies are an important laboratory for exploring galaxy formation and evolution. Automatic data analysis tools, such as cluster finding algorithms or mass and photometric redshift estimators, need to be tested prior to their use. We have launched a project to create realistic mock galaxy catalogs that will perform these tests accurately. This thesis project also includes development of tools to characterize clusters of galaxies, such as a red-sequence redshift estimator and an optical richness estimator. We also explore one of the candidates of contamination in cluster finding in sub-mm wavelength. The scientific goals to have been achieved are to build a realistic mock catalog on which several analysis tools are tested to better understand our ability to make accurate measurements; to develop an independent redshift and optical richness estimators with their applications to real clusters and to understand their systematics better to reduce the scatter; and to address a cautionary point in sub-mm cluster finding due to radio galaxies that are associated with clusters. These projects, in conjunction with each other, are demonstrated as crucial elements in constraining cosmological parameters to understand the evolution of the universe