Browsing by Author "Ho, Shirley"

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    LUMINOUS RED GALAXY POPULATION IN CLUSTERS AT 0.2 ≤ z ≤ 0.6
    (2009) Ho, Shirley; Lin, Yen-Ting; Spergel, David; Hirata, Christopher M.
    We investigate statistical properties of luminous red galaxies (LRGs) in a sample of X-ray-selected galaxy clusters at intermediate redshift (0.2 <= z <= 0.6) of mass range from similar to 1 x 10(14) M(circle dot) to similar to 8 x 10(14) M(circle dot). The LRGs are selected based on carefully designed color criteria, and the cluster membership is assessed via photometric redshifts. As clusters and LRGs are both viewed as promising tracer of the underlying dark matter distribution, understanding the distribution of LRGs within clusters is an important issue. Our main findings include ( 1) the halo occupation distribution ( HOD) of LRGs inside our cluster sample is < N(M)> = k(M/10(14)h(-1)M(circle dot)) a, where a = 0.495 +/- 0.105 and k = 1.455 +/- 0.285 assuming a Poisson distribution for N(M). If we assume the form of < N( M) > = 1 + k(M/10(14)h(-1)M(circle dot)) a, where a = 0.580 +/- 0.130 and k = 0.975 +/- 0.240 assuming a Poisson distribution for N( M). ( 2) The HOD of LRGs [ N( M)] and the satellite distribution of LRGs [N(M)-1] are both consistent with being Poisson. To be more quantitative, we find Var(N)/< N > = 1.43 +/- 0.35 and Var(N-1)/< N-1 > = 1.82 +/- 0.50. ( 3) The radial profile of LRGs within clusters when fitted with a Navarro-Frenk-White profile gives a concentration of 17.5(-4.3)(+7.1) (6.0(-1.9)(+3.2)) including (excluding) brightest LRGs (BLRGs). In essence, the BLRGs are more concentrated toward the center of the clusters than the other LRGs in clusters. We also discuss the implications of these observations on the evolution of massive galaxies in clusters.
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    PHOTOMETRIC SELECTION OF A MASSIVE GALAXY CATALOG WITH z >= 0.55
    (IOP PUBLISHING LTD, 2017) Nunez, Carolina; Spergel, David N.; Ho, Shirley
    We present the development of a photometrically selected massive galaxy catalog, targeting Luminous Red Galaxies (LRGs) and massive blue galaxies at redshifts of z. >= 0.55. Massive galaxy candidates are selected using infrared/optical color-color cuts, with optical data from the. Sloan Digital Sky Survey (SDSS) and infrared data from "unWISE" forced photometry derived from the Wide-field Infrared Survey Explorer (WISE). The selection method is based on previously developed techniques to select LRGs with z > 0.5, and is optimized using receiver operating characteristic curves. The catalog contains 16,191,145 objects, selected over the full SDSS DR10 footprint. The redshift distribution of the resulting catalog is estimated using spectroscopic redshifts from the DEEP2 Galaxy Redshift Survey and photometric redshifts from COSMOS. Restframe U - B colors from DEEP2 are used to estimate LRG selection efficiency. Using DEEP2, the resulting catalog has an. average redshift of z - 0.65, with a. standard deviation of sigma = 2.0, and an. average restframe of. U - B = 1.0, with a. standard deviation of sigma = 0.27. Using COSMOS, the resulting catalog has an. average redshift of z = 0.60, with a standard deviation of sigma = 1.8. We estimate 34% of the catalog to be blue galaxies with z >= 0.55. An estimated 9.6% of selected objects are blue sources with redshift z < 0.55. Stellar contamination is estimated to be 1.8%.