Shaping physical properties of galaxy subtypes in the VIPERS survey: Environment matters^⋆

¹ Institut de Física d’Altes Energies, The Barcelona Institute of Science and Technology, 08193 Bellaterra, Spain
e-mail: msiudek@ifae.es
² National Centre for Nuclear Research, ul. Pasteura 7, 02-093 Warsaw, Poland
³ Aix Marseille Univ., CNRS, CNES, LAM, Marseille, France
⁴ Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland
⁵ INAF – Osservatorio Astronomico di Brera, via Brera 2820122 Milano, Italy ; via E. Bianchi 46, 23807 Merate, Italy
⁶ Instituto de Astronomía y Ciencias Planetarias de Atacama (INCT), Universidad de Atacama, Copayapu 485, Copiapó, Chile
⁷ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
⁸ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, Via A. Corti 12, 20133 Milano, Italy
⁹ Institute of Physics, Jan Kochanowski University, ul. Swietokrzyska 15, 25-406 Kielce, Poland
¹⁰ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, Via Bassini 15, 20133 Milano, Italy
¹¹ Department of Astronomy & Physics and the Institute for Computational Astrophysics, Saint Mary’s University, 923 Robie Street, Halifax, Nova Scotia B3H 3C3, Canada

Received: 22 March 2022
Accepted: 27 May 2022

Abstract

Aims. This study aims to explore the relation between the physical properties of different galaxy sub-classes, from red passive to blue star-forming, and their environment. Our work is based on the analysis of 31 631 galaxies from the VIMOS Public Extragalactic Redshift Survey (VIPERS), observed at 0.5 <  z <  0.9. The unprecedented volume of VIPERS and the wealth of auxiliary derived data allow us to associate sub-classes of the main galaxy populations with their possibly different evolutionary paths. This is the first time such a study is performed with such statistical precision.

Methods. We use the results of an unsupervised clustering algorithm to distinguish 11 subclasses of VIPERS galaxies, based on the multi-dimensional feature space, defined by rest-frame UV to NIR colours. We investigate the relationship between the properties of these sub-classes of galaxies and their local environment, defined as the galaxy density contrast, δ, derived from the fifth nearest neighbour technique.

Results. We confirm that the galaxy population-density relation is already in place at z ∼ 0.9, with the blue galaxy fraction decreasing with density, compensated by an increase in the red fraction. We demonstrate how the properties of red, green, and blue galaxy subclasses are altered as they assemble into denser regions, and we attempt to interpret this in the context of their evolution. On average, red galaxies in the high-density environment are larger by 28% than those in low-density environments. In particular, we find one group of galaxies, sub-class C3, whose increase of size with time can be explained mainly as the result of mergers; for other red subclasses, mergers would not seem to play the major role (subclass C2) or would play a negligible role (sub-class C1). The properties of the green galaxies (sub-classes C4–6) depend on whether their stellar mass is above or below a transition mass, log(M_star/M_⊙)=10.6. Low-mass green (9.5 ≲ log(M_star/M_⊙)≲10.6) galaxies appear to have grown through secular processes, while in high-mass (10.6 ≲ log(M_star/M_⊙)≲11.5) green galaxies, mass assembly appears to be dominated by mergers. When it comes to blue galaxies, the trend of decreasing fraction with denser environments seen for the group as a whole (sub-classes C7–11) is found to be driven mostly by one (the most numerous) group of galaxies; sub-class C10. These are compact low-mass galaxies with high, specific star formation rates, which are preferentially found in low-density environments. However, the remaining blue galaxies (sub-classes C7–9) are larger and appear in denser environments than galaxies within C10.