ALBERT

Description: We simultaneously constrain cosmology and galaxy bias using measurements of galaxy abundances, galaxy clustering and galaxy–galaxy lensing taken from the Sloan Digital Sky Survey. We use the conditional luminosity function (which describes the halo occupation statistics as a function of galaxy luminosity) combined with the halo model (which describes the non-linear matter field in terms of its halo building blocks) to describe the galaxy–dark matter connection. We explicitly account for residual redshift-space distortions in the projected galaxy–galaxy correlation functions, and marginalize over uncertainties in the scale dependence of the halo bias and the detailed structure of dark matter haloes. Under the assumption of a spatially flat, vanilla cold dark matter (CDM) cosmology, we focus on constraining the matter density, m , and the normalization of the matter power spectrum, 8 , and we adopt 7-year Wilkinson Microwave Anisotropy Probe ( WMAP 7) priors for the spectral index, n , the Hubble parameter, h , and the baryon density, b . We obtain that m = 0.278 + 0.023 – 0.026 and 8 = 0.763 + 0.064 – 0.049 (95 per cent CL). These results are robust to uncertainties in the radial number density distribution of satellite galaxies, while allowing for non-Poisson satellite occupation distributions results in a slightly lower value for 8 (0.744 + 0.056 – 0.047 ). These constraints are in excellent agreement (at the 1 level) with the cosmic microwave background constraints from WMAP . This demonstrates that the use of a realistic and accurate model for galaxy bias, down to the smallest non-linear scales currently observed in galaxy surveys, leads to results perfectly consistent with the vanilla CDM cosmology.

Description: We use ROSAT All Sky Survey broad-band X-ray images and the optical clusters identified from Sloan Digital Sky Survey Data Release 7 to estimate the X-ray luminosities around ~65 000 candidate clusters with masses 10 13 h – 1 M based on an optical to X-ray ( otx ) code we develop. We obtain a catalogue with X-ray luminosity for each cluster. This catalogue contains 817 clusters (473 at redshift z ≤ 0.12) with signal-to-noise ratio 〉3 in X-ray detection. We find about 65 per cent of these X-ray clusters have their most massive member located near the X-ray flux peak; for the rest 35 per cent, the most massive galaxy is separated from the X-ray peak, with the separation following a distribution expected from a Navarro–Frenk–White profile. We investigate a number of correlations between the optical and X-ray properties of these X-ray clusters, and find that the cluster X-ray luminosity is correlated with the stellar mass (luminosity) of the clusters, as well as with the stellar mass (luminosity) of the central galaxy and the mass of the halo, but the scatter in these correlations is large. Comparing the properties of X-ray clusters of similar halo masses but having different X-ray luminosities, we find that massive haloes with masses 10 14 h – 1 M contain a larger fraction of red satellite galaxies when they are brighter in X-ray. An opposite trend is found in central galaxies in relative low-mass haloes with masses 10 14 h – 1 M where X-ray brighter clusters have smaller fraction of red central galaxies. Clusters with masses 10 14 h – 1 M that are strong X-ray emitters contain many more low-mass satellite galaxies than weak X-ray emitters. These results are also confirmed by checking X-ray clusters of similar X-ray luminosities but having different characteristic stellar masses. A cluster catalogue containing the optical properties of member galaxies and the X-ray luminosity is available at http://gax.shao.ac.cn/data/Group.html .