Mapping the kinetic Sunyaev-Zel’dovich effect toward MACS J0717.5+3745 with NIKA

¹ Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Boulevard de l’Observatoire, CS 34229, 06304 Nice Cedex 4, France
e-mail: remi.adam@oca.eu
² Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble Alpes, CNRS/IN2P3, 53 avenue des Martyrs, 38026 Grenoble, France
³ Laboratoire AIM, CEA/IRFU, CNRS/INSU, Université Paris Diderot, CEA-Saclay, 91191 Gif-Sur-Yvette, France
⁴ Astronomy Instrumentation Group, University of Cardiff, CF10 3 AT Cardiff, UK
⁵ Institut d’Astrophysique Spatiale (IAS), CNRS and Université Paris Sud, 91405 Orsay, France
⁶ Institut Néel, CNRS and Université Grenoble Alpes, 25 rue des Martyrs, BP 166, 38000 Grenoble, France
⁷ Institut de Radio Astronomie Millimétrique (IRAM), 18012 Granada, Spain
⁸ Dipartimento di Fisica, Università degli Studi di Roma “Tor Vergata”, via della Ricerca Scientifica, 1, 00133 Roma, Italy
⁹ Institut de Radio Astronomie Millimétrique (IRAM), 38406 Grenoble, France
¹⁰ Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 5, 00185 Roma, Italy
¹¹ Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), CNRS and Université Grenoble Alpes, 38058 Grenoble Cedex 9, France
¹² Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
¹³ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
¹⁴ School of Earth and Space Exploration and Department of Physics, Arizona State University, Tempe, AZ 85287, USA
¹⁵ European Organization for Astronomical Research in the Southern hemisphere, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
¹⁶ Université de Toulouse, UPS-OMP, Institut de Recherche en Astrophysique et Planétologie (IRAP), 31028 Toulouse Cedex 4, France
¹⁷ CNRS, IRAP, 9 avenue colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
¹⁸ Center for Detectors, School of Physics and Astronomy, Rochester Institute of Technology, Rochester, NY 14623, USA
¹⁹ Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA

Received: 24 June 2016
Accepted: 3 December 2016

Abstract

Measurement of the gas velocity distribution in galaxy clusters provides insight into the physics of mergers, through which large scale structures form in the Universe. Velocity estimates within the intracluster medium (ICM) can be obtained via the Sunyaev-Zel’dovich (SZ) effect, but its observation is challenging both in term of sensitivity requirement and control of systematic effects, including the removal of contaminants. In this paper we report resolved observations, at 150 and 260 GHz, of the SZ effect toward the triple merger MACS J0717.5+3745 (z = 0.55), using data obtained with the NIKA camera at the IRAM 30 m telescope. Assuming that theSZ signal is the sum of a thermal (tSZ) and a kinetic (kSZ) component and by combining the two NIKA bands, we extract for the first time a resolved map of the kSZ signal in a cluster. The kSZ signal is dominated by a dipolar structure that peaks at −5.1 and + 3.4σ, corresponding to two subclusters moving respectively away and toward us and coincident with the cold dense X-ray core and a hot region undergoing a major merging event. We model the gas electron density and line-of-sight velocity of MACS J0717.5+3745 as four subclusters. Combining NIKA data with X-ray observations from XMM-Newton and Chandra, we fit this model to constrain the gas line-of-sight velocity of each component, and we also derive, for the first time, a velocity map from kSZ data (i.e. that is model-dependent). Our results are consistent with previous constraints on the merger velocities, and thanks to the high angular resolution of our data, we are able to resolve the structure of the gas velocity. Finally, we investigate possible contamination and systematic effects with a special care given to radio and submillimeter galaxies. Among the sources that we detect with NIKA, we find one which is likely to be a high redshift lensed submillimeter galaxy.