CLASH-VLT: Galaxy cluster MACS J0329–0211 and its surroundings using galaxies as kinematic tracers

¹ Dipartimento di Fisica dell’Università degli Studi di Trieste – Sezione di Astronomia, Via Tiepolo 11, I-34143 Trieste, Italy
² INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, I-34143 Trieste, Italy
³ Fundación Galileo Galilei – INAF (Telescopio Nazionale Galileo), Rambla José Ana Fernández Perez 7, E-38712 Breña Baja (La Palma), Canary Islands, Spain
⁴ Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, E-38205 La Laguna (Tenerife), Canary Islands, Spain
⁵ Departamento de Astrofísica, Univ. de La Laguna, Av. del Astrofísico Francisco Sánchez s/n, E-38205 La Laguna (Tenerife), Spain
⁶ Dipartimento di Fisica E. R. Caianiello, Università Degli Studi di Salerno, Via Giovanni Paolo II, I-84084 Fisciano, (SA), Italy
⁷ INAF – Osservatorio Astronomico di Capodimonte, Via Moiariello 16, I-80131 Napoli, Italy
⁸ Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via Saragat 1, 44122 Ferrara, Italy
⁹ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
¹⁰ IFPU – Institute for Fundamental Physics of the Universe, Via Beirut 2, 34014 Trieste, Italy
¹¹ Institute of Astrophysics, Facultad de Ciencias Exactas, Universidad Andrés Bello, Sede Concepción, Talcahuano, Chile
¹² Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria 16, 20133 Milano, Italy
¹³ INAF – IASF Milano, Via A. Corti 12, 20133 Milano, Italy
¹⁴ University Observatory, Ludwig-Maximilians University Munich, Scheinerstrasse 1, 81679 Munich, Germany
¹⁵ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 50125 Firenze, Italy

^⋆ Corresponding author; marisa.girardi@inaf.it

Received: 27 June 2024
Accepted: 24 October 2024

Abstract

Context. The study of substructure is an important step in determining how galaxy clusters form.

Aims. We aim to gain new insights into the controversial dynamical status of MACS J0329–0211 (MACS0329), a massive cluster at z = 0.4503 ± 0.0003, through a new analysis using a large sample of member galaxies as kinematic tracers.

Methods. Our analysis is based on extensive spectroscopic data for more than 1700 galaxies obtained with the VIMOS and MUSE spectrographs at the Very Large Telescope (VLT) in combination with B and R_C Suprime-Cam photometry from the Subaru archive. According to our member selection procedure, we defined a sample of 430 MACS0329 galaxies within 6 Mpc, corresponding to approximately three times the virial radius.

Results. We estimated the global velocity dispersion, σ_V841_-36⁺²⁶ km s⁻¹, and present the velocity dispersion profile. We estimated a mass of M₂₀₀ = (9.2 ± 1.5)×10¹⁴ M_⊙ using 227 galaxies within R₂₀₀ = (1.71 ± 0.07) Mpc, for which σ_V,200841_-48⁺⁴⁰ km s⁻¹. The spatial distribution of the red galaxies traces a SE-NW elongated structure without signs of a velocity gradient. This structure likely originates from the main phase of cluster assembly. The distribution of the blue galaxies is less concentrated and more rounded, and it shows signs of substructure, all characteristics indicating a recent infall of groups from the field. We detected two loose clumps of blue galaxies in the south and southwest at a distance of ∼R₂₀₀ from the cluster center. The strong spatial segregation among galaxy populations is not accompanied by a kinematical difference. Thanks to our extensive catalog of spectroscopic redshift, we were able to study galaxy systems that are intervening along the line of sight. We identified two foreground galaxy systems, GrG1 at z ∼ 0.31 and GrG2 at z ∼ 0.38, and one background system, GrG3 at z ∼ 0.47. We point out that the second brightest galaxy projected onto the MACS0329 core is in fact the dominant galaxy of the foreground group GrG2. MACS0329, GrG3, and two other systems detected using DESI DR9 photometric redshifts are close to each other, suggesting the presence of a large-scale structure.

Conclusions. MACS0329 is close to a state of dynamical equilibrium despite being surrounded by a very rich environment. We emphasize that the use of an extensive spectroscopic redshift survey is essential to avoiding misinterpretation of structures projected along the line of sight.