ThePlanckSZ Cluster Catalog: expected X-ray properties

Abstract

Surveys based on the Sunyaev-Zel'dovich (SZ) effect provide a fresh view of the galaxy cluster population, one that is complementary to X-ray surveys. To better understand the relation between these two kinds of survey, we construct an empirical cluster model using scaling relations constrained by current X-ray and SZ data. We apply our model to predict the X-ray properties of the Planck SZ Cluster Catalog (PCC) and compare them to existing X-ray cluster catalogs. We find that Planck should significantly extend the depth of the previous all-sky cluster survey, performed in the early 1990s by the ROSAT satellite, and should be particularly effective at finding hot, massive clusters (T > 6 keV) out to redshift unity. These are rare objects, and our findings suggest that Planck could increase the observational sample at z > 0.6 by an order of magnitude. This would open the way for detailed studies of massive clusters out to these higher redshifts. Specifically, we find that the majority of newly-detected Planck clusters should have X-ray fluxes 10 −13 erg/s/cm 2 < f X [0.5−2 keV] < 10 −12 erg/s/cm 2 , i.e., distributed over the decade in flux just below the ROSAT All Sky Survey limit. This is sufficiently bright for extensive X-ray follow-up campaigns. Once Planck finds these objects, XMM-Newton and Chandra could measure temperatures to 10% for a sample of ∼100 clusters in the range 0.5 < z < 1, a valuable increase in the number of massive clusters studied over this range.

Planck2015 results

“…This is illustrated in Fig. 4 of Chamballu et al (2012) for the MCXC. This allows us to characterize our completeness by checking if the fraction of detected clusters follows the expected probability distribution as a function of their parameters.…”

A comparison of algorithms for the construction of SZ cluster catalogues

“…In that respect, the use of X-ray information from the ROSAT All-Sky Survey (RASS) cluster catalogues (Böhringer et al 2000(Böhringer et al , 2004Piffaretti et al 2011) or from optical catalogues, e.g. in the SDSS area (Koester et al 2007), will be of particular value as they will give us a handle on both flux and size of the clusters detected by Planck and, even more importantly, understand better the completeness in studying those which are missed (Chamballu et al 2012). As already stated, the exact position of each selection curve in Fig.…”

Planck2015 results

“…Details are given in the 2015 SZ catalogue paper, Planck Collaboration XXVII (2016). For the MCXC compilation, we rely on the expectation that at redshifts z < 0.2 any Planck-detected cluster should be found in one of the ROSAT catalogues (Chamballu et al 2012) because at low redshift ROSAT probes to lower masses than Planck 6 . The MCXC catalogue provides a truth table, replacing the input cluster list of the simulations, and we compute completeness as the ratio of objects in the cosmology catalogue to the total number of clusters.…”