Abstract
We present further results from the ongoing XMM-Newton validation follow-up of Planck cluster candidates, detailing X-ray observations of eleven candidates detected at a signal-to-noise ratio of 4.5<S/N<5.3 in the same 10-month survey maps used in the construction of the Early SZ sample. The sample was selected in order to test internal SZ quality flags, and the pertinence of these flags is discussed in light of the validation results. Ten of the candidates are found to be bona fide clusters lying below the RASS flux limit. Redshift estimates are available for all confirmed systems via X-ray Fe-line spectroscopy. They lie in the redshift range 0.19<z<0.94, demonstrating Planck's capability to detect clusters up to high z. The X-ray properties of the new clusters appear to be similar to previous new detections by Planck at lower z and higher SZ flux: the majority are X-ray underluminous for their mass, estimated using Y_X as mass proxy, and many have a disturbed morphology. We find tentative indication for Malmquist bias in the Y_SZ-Y_X relation, with a turnover at Y_SZ \sim 4 e-4 arcmin^2. We present additional new optical redshift determinations with ENO and ESO telescopes of candidates previously confirmed with XMM-Newton. The X-ray and optical redshifts for a total of 20 clusters are found to be in excellent agreement. We also show that useful lower limits can be put on cluster redshifts using X-ray data only via the use of the Y_X vs. Y_SZ and X-ray flux F_X vs. Y_SZ relations.
Highlights
The deep potential wells in clusters of galaxies make them unique laboratories in which to study astrophysical processes linked to gas physics, galaxy formation, and feedback.Article published by EDP SciencesA102, page 1 of 14A&A 543, A102 (2012)since clusters trace the highest peaks of the matter density field, the properties of the cluster population and their evolution are a sensitive cosmological probe.The recent advent of increased sensitivity and survey capability has transformed galaxy cluster searches via the SunyaevZeldovich (SZ) effect
The offset between the X-ray position and the Planck position (Fig. 2) is similar to that observed for known clusters in the Early SZ (ESZ) sample (Planck Collaboration 2011b) or for candidates that have previously been confirmed with XMM-Newton (Planck Collaboration 2011c)
Y500 is the spherically integrated Compton parameter measured with Planck, centred on the X-ray peak, interior to the R500 estimated with the X-ray observations.(†) Other possible zFe: 0.02, 0.82; the best estimate, zFe = 0.21 is consistent with the optical photometric redshift. (‡) Other possible zFe: 0.19, 0.82; the best estimate, zFe = 0.59 is consistent with the optical photometric redshift. (∗) Other possible zFe: 0.12, 0.87, 1.20
Summary
J. Davis, P. de Bernardis, G. de Gasperis, G. de Zotti, J.
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