Weak‐Lensing Measurements of 42 SDSS/RASS Galaxy Clusters

Abstract

We present a lensing study of 42 galaxy clusters imaged in Sloan Digital Sky Survey (SDSS) commissioning data. Cluster candidates are selected optically from SDSS imaging data and confirmed for this study by matching to X-ray sources found independently in the ROSAT All-Sky Survey (RASS). Five-color SDSS photometry is used to make accurate (Δz = 0.018) photometric redshift estimates that are used to rescale and combine the lensing measurements. The mean shear from these clusters is detected to 2 h-1 Mpc at the 7 σ level, corresponding to a mass within that radius of (4.2 ± 0.6) × 1014 h-1 M☉. The shear profile is well fitted by a power law with index -0.9 ± 0.3, consistent with that of an isothermal density profile. Clusters are divided by X-ray luminosity into two subsets, with mean LX of (0.14 ± 0.03) × 1044 and (1.0 ± 0.09) × 1044 h-2 ergs s-1. The average lensing signal is converted to a projected mass density based on fits to isothermal density profiles. From this we calculate a mean r500 (the radius at which the mean density falls to 500 times the critical density) and M(<r500). The mass contained within r500 differs substantially between the low- and high-LX bins, with (0.7 ± 0.2) × 1014 and 2.7×1014 h-1 M☉, respectively. This paper demonstrates our ability to measure ensemble cluster masses from SDSS imaging data. The full SDSS data set will include 1000 SDSS/RASS clusters. With this large data set we will measure the M-LX relation with high precision and put direct constraints on the mass density of the universe.