Stacking clusters in the ROSAT All-Sky Survey

Max-Planck-Institut für Astrophysik, PO Box 1317, 85741 Garching, Germany

Corresponding author: M.Bartelmann, msb@mpa-garching.mpg.de

Received: 2 October 2002
Accepted: 25 June 2003

Abstract

Ongoing and planned wide-area surveys at optical and infrared wavelengths should detect a few times 10⁵ galaxy clusters, roughly of which are expected to be at redshifts ≳0.8. We investigate what can be learned about the X-ray emission of these clusters from the ROSAT All-Sky Survey. While individual clusters at redshifts ≳0.5 contribute at most a few photons to the survey, a significant measurement of the mean flux of cluster subsamples can be obtained by stacking cluster fields. We show that the mean X-ray luminosity of clusters with mass selected from the Sloan Digital Sky Survey should be measurable out to redshift unity with signal-to-noise ≳10, even if clusters are binned with and . For such bins, a suitably chosen hardness ratio allows the mean temperature of clusters to be determined out to with a relative accuracy of for .