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Detailed Sunyaev–Zel’dovich study with AMI of 19 LoCuSS galaxy\ud clusters: masses and temperatures out to the virial radius

By Carmen Rodríguez-Gonzálvez, Timothy W. Shimwell, Matthew L. Davies, Farhan Feroz, Thomas M. O. Franzen, Keith J. B. Grainge, Michael P. Hobson, Natasha Hurley-Walker, Anthony N. Lasenby, Malak Olamaie, Guy Pooley, Richard D. E. Saunders, Anna M. M. Scaife, Michel P. Schammel, Paul F. Scott, David J. Titterington and Elizabeth M. Waldram

Abstract

We present detailed 16-GHz interferometric observations using the Arcminute Microkelvin Imager (AMI) of 19 clusters with L_X > 7 × 10^(37) W (h_(50) = 1) selected from the Local Cluster Substructure Survey (LoCuSS; 0.142 ≤ z ≤ 0.295) and of Abell 1758b, which is in the field of view of Abell 1758a. We detect and resolve Sunyaev–Zel'dovich (SZ) signals towards 17 clusters, with peak surface brightnesses between 5σ and 23σ. We use a fast, Bayesian cluster analysis to obtain cluster parameter estimates in the presence of radio point sources, receiver noise and primordial cosmic microwave background (CMB) anisotropy. We fit isothermal β-models to our data and assume the clusters are virialized (with all the kinetic energy in gas internal energy). Our gas temperature, T_(AMI), is derived from AMI SZ data and not from X-ray spectroscopy. Cluster parameters internal to r_(500) are derived under the assumption of hydrostatic equilibrium. We find the following. (i) Different generalized Navarro–Frenk–White (gNFW) parametrizations yield significantly different parameter degeneracies. (ii) For h_(70) = 1, we find the classical virial radius, r_(200), to be typically 1.6 ± 0.1 Mpc and the total mass M_T(r_(200)) typically to be 2.0–2.5× M_T(r_(500)). (iii) Where we have found M_T(r_(500)) and M_T(r_(200)) X-ray and weak-lensing values in the literature, there is good agreement between weak-lensing and AMI estimates (with M_(T,AMI)/M_(T,WL) = 1.2^(+0.2)_(−0.3) and 1.0 ± 0.1 for r_(500) and r_(200), respectively). In comparison, most Suzaku/Chandra estimates are higher than for AMI (with M_(T,X)/M_(T,AMI) = 1.7 ± 0.2 within r_(500)), particularly for the stronger mergers. (iv) Comparison of T_(AMI) to T_X sheds light on high X-ray masses: even at large radius, T_X can substantially exceed T_(AMI) in mergers. The use of these higher T_X values will give higher X-ray masses. We stress that large-radius T_(AMI) and T_X data are scarce and must be increased. (v) Despite the paucity of data, there is an indication of a relation between merger activity and SZ ellipticity. (vi) At small radius (but away from any cooling flow) the SZ signal (and T_(AMI)) is less sensitive to intracluster medium disturbance than the X-ray signal (and T_X) and, even at high radius, mergers affect n^2-weighted X-ray data more than n-weighted SZ, implying that significant shocking or clumping or both occur in even the outer parts of mergers

Publisher: Royal Astronomical Society
Year: 2012
OAI identifier: oai:authors.library.caltech.edu:34787
Provided by: Caltech Authors

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