A newly identified galaxy group thanks to tidal streams of intragroup light^⋆

¹ Dipartimento di Fisica dell’Università degli Studi di Trieste – Sezione di Astronomia, Via Tiepolo 11, 34143 Trieste, Italy
² INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34143 Trieste, Italy
e-mail: marisa.girardi@inaf.it
³ Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁴ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
⁵ Fundación Galileo Galilei – INAF (Telescopio Nazionale Galileo), Rambla José Ana Fernández Perez 7, 38712 Breña Baja (La Palma), Canary Islands, Spain
⁶ Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38205 La Laguna (Tenerife), Canary Islands, Spain
⁷ Departamento de Astrofísica, Univ. de La Laguna, Av. del Astrofísico Francisco Sánchez s/n, 38205 La Laguna, Tenerife, Spain
⁸ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica di Milano, Via A. Corti 12, I-20133 Milano, Italy
⁹ Dipartimento di Fisica E.R. Caianiello, Università Degli Studi di Salerno, Via Giovanni Paolo II, 84084 Fisciano, SA, Italy
¹⁰ INAF – Osservatorio Astronomico di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy
¹¹ Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via Saragat 1, 44122 Ferrara, Italy

Received: 1 August 2022
Accepted: 24 January 2023

Abstract

Context. In the accretion-driven growth scenario, part of the intracluster light is formed in the group environment.

Aims. We report the serendipitous discovery of a group of galaxies with signs of diffuse light in the foreground of the known galaxy cluster MACS J0329−0211 at z ∼ 0.45.

Methods. Our investigation began with the detection of diffuse light streams around a pair of bright galaxies in the southeastern region of a Suprime-Cam image of the galaxy cluster MACS J0329-0211. Our analysis is based on the extended CLASH-VLT redshift catalog and on new spectroscopic data obtained ad hoc with the Italian Telescopio Nazionale Galileo. We use the density reconstruction method to analyze the redshift distribution of the galaxies in the region around the galaxy pair. We also use available photometric and X-ray data to better characterize the properties of the group.

Results. Thanks to the large amount of redshift data collected in this region, we have been able to discover the existence of a group of galaxies, here called GrG J0330−0218, which is associated with the pair of galaxies. These are the two brightest group galaxies (BGG1 and BGG2). We extracted 41 group members from the redshift catalog and estimate a mean redshift z = 0.1537 and a line-of-sight velocity dispersion σ_v ∼ 370 km s⁻¹. In the phase-space diagram, the distribution of the galaxies of GrG J0330-0218 follows the characteristic trumpet-shaped pattern, which is related to the escape velocity of galaxy clusters, suggesting that the group is a virialized structure. Under this assumption, the mass of the group is M₂₀₀ ∼ 6 × 10¹³ M_⊙. We also measured a mass-to-light ratio of ∼130 M_⊙/L_⊙ and a luminosity fraction of diffuse light of ∼20% within 0.5 R₂₀₀.

Conclusions. We conjecture that galaxy pairs that are surrounded by diffuse light, probably due to tidal interactions, can serve as signposts for groups.