Understanding the role of morphology and environment in the dynamical evolution of isolated galaxy triplets^⋆

¹ Instituto de Física, Pontificia Universidad Católica de Valparaíso, Casilla 4059 Valparaíso, Chile
e-mail: paulo.vasquez.b@mail.pucv.cl
² Universidad de Granada (UGR), Departamento de Física Teórica y del Cosmos, Campus Fuente Nueva, Edificio Mecenas, 18071 Granada, Spain
³ Instituto Universitario Carlos I de Física Teórica y Computacional, Universidad de Granada, 18071 Granada, Spain
⁴ Facultad de Ingeniería, Departamento de Ciencias Básicas, Universidad Ean, Cl. 71 #9–84, Localidad de Chapinero, Bogotá, Cundinamarca, Colombia
⁵ Département de Physique, de Génie Physique et d’Optique, Université Laval, and Centre de Recherche en Astrophysique du Québec (CRAQ), Québec, QC G1V 0A6, Canada
⁶ Instituto de Astrofísica de Andalucía – CSIC, Glorieta de la Astronomía s.n., 18008 Granada, Spain

Received: 26 October 2022
Accepted: 16 November 2022

Abstract

Context. The environments where galaxies reside affects their evolutionary histories. Galaxy triplets (systems composed of three physically bound galaxies) are one of simplest groups of galaxies, and are therefore excellent laboratories to study evolutionary mechanisms where effects of the environment are minimal.

Aims. We present a statistical study of the dynamical properties of isolated galaxy triplets as a function of their local and large-scale environments. To explore the connection of the dynamical evolution on the systems with the evolution of the galaxies composing the triplets, we consider observational properties such as morphology and star formation rate (SFR).

Methods. We used the SDSS-based catalogue of Isolated Triplets (SIT), which contains 315 triplets. We classified each triplet according to galaxy morphologies and defined a parameter Q_trip to quantify the total local tidal strengths in the systems. To quantify the dynamical stage of the system we used the parameters of harmonic radius R_H, velocity dispersion σ_vr, crossing time H₀t_c, and virial mass M_vir.

Results. Triplets composed of three early-type galaxies present the smallest R_H, indicating that they are in general more compact than triplets with one or more late-type galaxies. Among triplets with low values of R_H and H₀t_c, SIT triplets with Q_trip < −2 are relaxed systems that are more dynamically evolved, while triplets with Q_trip > −2 show compact configurations due to interactions within the system, such as ongoing mergers.

Conclusions. We found that there is no dominant galaxy in triplets in terms of properties of stellar populations such as global colour and SFR. Moreover, the global SFR in isolated triplets composed of two or more early-type galaxies increases with the stellar mass ratio of the galaxies with respect to the central galaxy, therefore the system is globally ‘rejuvenated’.