CLASH-VLT: Substructure in the galaxy cluster MACS J1206.2-0847 from kinematics of galaxy populations^⋆,⋆⋆

¹ Dipartimento di FisicaUniversità degli Studi di Trieste, via Tiepolo 11, 34143 Trieste, Italy
e-mail: girardi@oats.inaf.it
² INAF/Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34133, Trieste, Italy
³ INAF/Osservatorio Astronomico di Capodimonte, via Moiariello 16 80131 Napoli, Italy
⁴ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁵ Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Ferrara, via Saragat 1, 44122 Ferrara, Italy
⁶ Department of Astronomy, Universidad de Concepcion, Casilla 160-C, Concepcion, Chile
⁷ INAF/IASF-Milano, via Bassini 15, 20133 Milano, Italy
⁸ Korea Institute for Advanced Study, KIAS, 85 Hoegiro, 130-722 Dongdaemun-gu Seoul, Republic of Korea
⁹ Department of Physics and Astronomy, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
¹⁰ INAF/Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹¹ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹² Observatories of the Carnegie Institution of Washington, Pasadena, CA 91 101, USA
¹³ Dipartimento di Fisica, Università degli Studi di Milano, via Celoria 16, 20133 Milan, Italy
¹⁴ Institute of Astronomy and Astrophysics, Academia Sinica, PO Box 23-141, 10617 Taipei, Taiwan
¹⁵ California Institute of Technology, MC 249-17, Pasadena, CA 91125, USA
¹⁶ Fundaciòn Galileo Galilei−INAF, Rambla José Ana Fernández Pérez 7, 38712 Breña Baja, La Palma, Spain
¹⁷ Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
¹⁸ Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
¹⁹ University of Vienna, Department of Astrophysics, Türkenschanzstr. 17, 1180 Wien, Austria
²⁰ INAF/Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
²¹ INFN, Sezione di Bologna, via Ranzani 1, 40127 Bologna, Italy
²² Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
²³ University Observatory Munich, Scheinerstrasse 1, 81679 München, Germany
²⁴ Max-Planck-Institut für extraterrestrische Physik, Posfatch 1312, Giessenbachstr., 85741 Garching, Germany

Received: 30 December 2014
Accepted: 16 March 2015

Abstract

Aims. In the effort to understand the link between the structure of galaxy clusters and their galaxy populations, we focus on MACS J1206.2-0847 at z ~ 0.44 and probe its substructure in the projected phase space through the spectrophotometric properties of a large number of galaxies from the CLASH-VLT survey.

Methods. Our analysis is mainly based on an extensive spectroscopic dataset of 445 member galaxies, mostly acquired with VIMOS at VLT as part of our ESO Large Programme, sampling the cluster out to a radius ~2R₂₀₀ (4 h₇₀^-1 Mpc). We classify 412 galaxies as passive, with strong Hδ absorption (red and blue galaxies), and with emission lines from weak to very strong. A number of tests for substructure detection are applied to analyze the galaxy distribution in the velocity space, in 2D space, and in 3D projected phase-space.

Results. Studied in its entirety, the cluster appears as a large-scale relaxed system with a few secondary, minor overdensities in 2D distribution. We detect no velocity gradients or evidence of deviations in local mean velocities. The main feature is the WNW-ESE elongation. The analysis of galaxy populations per spectral class highlights a more complex scenario. The passive galaxies and red strong Hδ galaxies trace the cluster center and the WNW-ESE elongated structure. The red strong Hδ galaxies also mark a secondary, dense peak ~2 h₇₀^-1 Mpcat ESE. The emission line galaxies cluster in several loose structures, mostly outside R₂₀₀. Two of these structures are also detected through our 3D analysis. The observational scenario agrees with MACS J1206.2-0847 having WNW-ESE as the direction of the main cluster accretion, traced by passive galaxies and red strong Hδ galaxies. The red strong Hδ galaxies, interpreted as poststarburst galaxies, date a likely important event 1−2 Gyr before the epoch of observation. The emission line galaxies trace a secondary, ongoing infall where groups are accreted along several directions.