We describe updates to the redMaPPer algorithm, a photometric red-sequence cluster finder specifically designed for large photometric surveys. The updated algorithm is applied to 150 deg 2 of Science Verification (SV) data from the Dark Energy Survey (DES), and to the Sloan Digital Sky Survey (SDSS) DR8 photometric data set. The DES SV catalog is locally volume limited, and contains 786 clusters with richness λ > 20 (roughly equivalent to M 500c 10 14 h −1 70 M ) and 0.2 < z < 0.9. The DR8 catalog consists of 26311 clusters with 0.08 < z < 0.6, with a sharply increasing richness threshold as a function of redshift for z 0.35. The photometric redshift performance of both catalogs is shown to be excellent, with photometric redshift uncertainties controlled at the σ z /(1 + z) ∼ 0.01 level for z 0.7, rising to ∼ 0.02 at z ∼ 0.9 in DES SV. We make use of Chandra and XMM X-ray and South Pole Telescope Sunyaev-Zeldovich data to show that the centering performance and massrichness scatter are consistent with expectations based on prior runs of redMaPPer on SDSS data. We also show how the redMaPPer photo-z and richness estimates are relatively insensitive to imperfect star/galaxy separation and small-scale star masks.

A B S T R A C TThe observed evolution of the galaxy cluster X-ray integral temperature distribution function between z 0:05 and z 0:32 is used in an attempt to constrain the value of the density parameter, Q 0 , for both open and spatially¯at universes. We estimate the overall uncertainty in the determination of both the observed and predicted galaxy cluster X-ray integral temperature distribution functions at z 0:32 by carrying out Monte Carlo simulations, where we take into careful consideration all the most important sources of possible error. We include the effect of the formation epoch on the relation between virial mass and X-ray temperature, improving on the assumption that clusters form at the observed redshift which leads to an overestimate of Q 0 . We conclude that at present both the observational data and the theoretical modelling carry suf®ciently large associated uncertainties to prevent an unambiguous determination of Q 0 . We ®nd that values of Q 0 around 0.75 are most favoured, with Q 0 < 0:3 excluded with at least 90 per cent con®dence. In particular, the Q 0 1 hypothesis is found to be still viable as far as this data set is concerned. As a by-product, we also use the revised data on the abundance of galaxy clusters at z 0:05 to update the constraint on j 8 given by Viana & Liddle, ®nding slightly lower values than before.

We use Chandra X-ray and Spitzer infrared (IR) observations to explore the active galactic nucleus (AGN) and starburst populations of XMMXCS J2215.9−1738 at z = 1.46, one of the most distant spectroscopically confirmed galaxy clusters known. The high-resolution X-ray imaging reveals that the cluster emission is contaminated by point sources that were not resolved in XMM-Newton observations of the system, and have the effect of hardening the spectrum, leading to the previously reported temperature for this system being overestimated. From a joint spectroscopic analysis of the Chandra and XMM-Newton data, the cluster is found to have temperature T = 4.1 +0.6 −0.9 keV and luminosity L X = (2.9244 erg s −1 , extrapolated to a radius of 2 Mpc. As a result of this revised analysis, the cluster is found to lie on the σ v -T relation, but the cluster remains less luminous than would be expected from self-similar evolution of the local L X -T relation. Two of the newly discovered X-ray AGNs are cluster members, while a third object, which is also a prominent 24 µm source, is found to have properties consistent with it being a high-redshift, highly obscured object in the background. We find a total of eight >5σ 24 µm sources associated with cluster members (four spectroscopically confirmed and four selected using photometric redshifts) and one additional 24 µm source with two possible optical/near-IR counterparts that may be associated with the cluster. Examining the Infrared Array Camera colors of these sources, we find that one object is likely to be an AGN. Assuming that the other 24 µm sources are powered by star formation, their IR luminosities imply star formation rates ∼100 M ⊙ yr −1 . We find that three of these sources are located at projected distances of <250 kpc from the cluster center, suggesting that a large amount of star formation may be taking place in the cluster core, in contrast to clusters at low redshift.