Planck Early Results VIII: The all-sky Early Sunyaev-Zeldovich cluster sample

TL;DR

This paper presents the first all-sky sample of galaxy clusters detected via the Sunyaev-Zeldovich effect by the Planck satellite, including known and new clusters with high reliability and a wide range of masses and redshifts.

Contribution

It provides the first all-sky SZ-selected galaxy cluster sample with extensive validation, including new cluster candidates and confirmation through follow-up observations.

Findings

189 high-confidence SZ cluster candidates identified

80% of known ESZ clusters have measured SZ signals

12 new clusters confirmed, mostly with disturbed morphologies

Abstract

We present the first all-sky sample of galaxy clusters detected blindly by the Planck satellite through the Sunyaev-Zeldovich (SZ) effect from its six highest frequencies. This early SZ (ESZ) sample is comprised of 189 candidates, which have a high signal-to-noise ratio ranging from 6 to 29. Its high reliability (purity above 95%) is further ensured by an extensive validation process based on Planck internal quality assessments and by external cross-identification and follow-up observations. Planck provides the first measured SZ signal for about 80% of the 169 previously-known ESZ clusters. Planck furthermore releases 30 new cluster candidates, amongst which 20 meet the ESZ signal-to-noise selection criterion. At the submission date, twelve of the 20 ESZ candidates were confirmed as new clusters, with eleven confirmed using XMM-Newton snapshot observations, most of them with disturbed morphologies and low luminosities. The ESZ clusters are mostly at moderate redshifts (86% with z below 0.3) and span more than a decade in mass, up to the rarest and most massive clusters with masses above 10^15 Msol.