The Bright SHARC survey: The selection function and its impact on the Cluster X-Ray Luminosity Function

We present the results of a comprehensive set of simulations designed to qu antify the selection function of the Bright SHARC survey for distant cluste rs. The statistical significance of the simulations relied on the creation of many thousands of artificial clusters with redshifts and luminosities in the range 0.25 < z < 0.95 and 0.5 < L-X < 10 x 10(44) ergs s(-1) (0.5-2.0 keV). We created one standard and 19 varied distribution functions, each of which assumed a different set of cluster; cosmological and operational par ameters. The parameters we varied included the values of Omega (0), Omega ( Lambda), beta, core radius (r(c)), and ellipticity (e). We also investigate d how nonstandard surface brightness profiles (i.e., the Navarro, Frenk, & White, or NFW, model); cooling flows; and the ROSAT pointing target, influe nce the selection function in the Bright SHARC survey. For our standard set we adopted the parameters used during the derivation of the Bright SHARC C luster X-Ray Luminosity Function (CXLF), i.e., Omega (0) = 1, Omega (Lambda ) = 0 and an isothermal beta model with beta = 0.67, r(c) = 250 kpc, and e = 0.15. We found that certain parameters have a dramatic effect, on our abi lity to detect clusters, e.g., the presence of a NFW profile or a strong co oling flow profile, or the value of r(c) and beta. Other parameters had ver y little effect, e.g., the type of ROSAT target and the cluster ellipticity . At distant redshift (z > 0.8), elliptical clusters are significantly easi er to detect than spherical ones in the Bright SHARC survey. We show also t hat all the tested parameters have only a small influence on the computed l uminosity of the dusters (" recovered luminosity" in the text) except the p resence of a strong cooling flow. We conclude that the CXLF presented by Ni chol et al. in 1999 is robust (under the assumption of standard parameters) , but stress the importance of cluster follow-up, by Chandra and XMM, in or der to better constrain the morphology of the distant clusters found in the Bright SHARC and other surveys.