Measuring the X-ray luminosities of SDSS DR7 clusters from ROSAT All Sky Survey

Abstract

We use ROSAT All Sky Survey (RASS) broadband X-ray images and the optical clusters identified from SDSS DR7 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 catalog contains 817 clusters (473 at redshift z ≤ 0.12) with S/N > 3 in X-ray detection. We find about 65% of these X-ray clusters have their most massive member located near the X-ray flux peak; for the rest 35%, the most massive galaxy is separated from the X-ray peak, with the separation following a distribution expected from a NFW 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 halos 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 halos 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 catalog containing the optical properties of member galaxies and the X-ray luminosity is available at

Smaller stellar disc scale lengths in rich environments

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“…5 show that galaxy disc scale length depends on group X-ray brightness. However, since the scatter in the X-ray luminosity for a given group is large (of order 0.4 dex in Wang et al 2014), we also look at our trends in disc scale length at fixed bulge mass for the extreme ends of the L x − M halo plane (samples are labelled ex-XRS and ex-XRW in Fig. 1) to ensure that the trends we observe with X-ray brightness are robust.…”

VIMOS Ultra-Deep Survey (VUDS): Witnessing the assembly of a massive cluster atz~ 3.3

“…Errors are determined from those in the velocity dispersion. The halo mass estimated from this calculation is enormous, enough to rival the most massive galaxy clusters observed in the local universe (e.g., Piffaretti et al 2011;Wang et al 2014). However, the number of assumptions, their associated uncertainties, and the formal errors coming from the velocity dispersion calculation are also enormous.…”

Galaxy–Galaxy Weak-lensing Measurements from SDSS. I. Image Processing and Lensing Signals

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