Galaxy evolution in compact groups

II. Witnessing the influence of major structures in their evolution

¹ Departamento de Astronomía, Universidad de La Serena, Avda. Raúl Bitrán 1305, La Serena, Chile
² Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo, Cidade Universitŕia, CEP:05508-900, São Paulo, SP, Brazil
³ Instituto Multidisciplinario de Investigación y Postgrado, Universidad de La Serena, Avda. Raúl Bitrán 1305, La Serena, Chile
⁴ Observatório do Valongo, Universidade Federal do Rio de Janeiro, Ladeira Pedro Antônio 43, Rio de Janeiro, RJ 20080-090, Brazil
⁵ Observatório Nacional, Rua General José Cristino, 77, São Cristóvão, 20921-400 Rio de Janeiro, RJ, Brazil
⁶ Laboratório Nacional de Astrofísica, R. dos Estados Unidos, 154 – Nações, Itajubá, MG 37504-364, Brazil
⁷ CONICET, Instituto de Astronomía Teorica y Experimental (IATE), Laprida 854, Córdoba X5000BGR, Argentina
⁸ Observatorio Astronómico de Córdoba (OAC), Universidad Nacional de Córdoba (UNC), Laprida 854, Córdoba X5000BGR, Argentina
⁹ Universidad de Investigación y Desarrollo, Departamento de Ciencias Básicas y Humanas, Grupo FIELDS, Calle 9 No. 23-55, Bucaramanga, Colombia
¹⁰ Departamento de Tecnologías Industriales, Facultad de Ingeniería, Universidad de Talca, Los Niches km 1, Curicó, Chile
¹¹ Institute of Astrophysics, Facultad de Ciencias Exactas, Universidad Andrés Bello, Sede Concepción, Talcahuano, Chile
¹² Departamento de Física, Universidade Federal de Santa Catarina, Florianópolis, SC 88040-900, Brazil
¹³ NOAO, 950 North Cherry Ave, Tucson, AZ 85719, USA
¹⁴ GMTO Corporation, N. Halstead Street 465, Suite 250, Pasadena, CA 91107, USA

^⋆ Corresponding author; gissel.pardo@userena.cl

Received: 20 June 2024
Accepted: 10 March 2025

Abstract

Compact groups (CGs) of galaxies are an extreme environment for the morphological transformations and the cessation of star formation in galaxies. However, despite initially being conceived as isolated systems, it is now widely recognised that many of them are not as isolated as expected. Our objective is to understand the dynamics of CGs, as well as how the environment surrounding CGs impacts their morphological and physical properties. To achieve this, we selected a sample of 316 CGs in the Stripe 82 region, with a total of 1011 galaxies, and a sample of 2281 field galaxies as a control sample. We find that at least 41% of our sample of CGs are part of major structures, i.e. non-isolated CGs. We find a bimodality in the effective radius (R_e)-Sérsic index (n) plane for all transition galaxies (those with (u − r) > 2.3 and n < 2.5) in CGs. Additionally, transition galaxies in isolated CGs populate more densely the R_e − n plane for n < 1.75. In contrast, transition galaxies in non-isolated CGs show a bimodal distribution in the R_e − n plane, with the n values smoothly increasing towards higher values, and 62% of these galaxies having n > 1.5. This indicates that the majority of these galaxies have already undergone a morphological transformation and primarily contribute to the population of more compact galaxies in the R_e − n plane. We find that galaxies in our sample of CGs have a lower mean specific star formation rate (sSFR) compared to the control sample, with non-isolated CGs showing even lower sSFR values, indicating that dense environments suppress star formation. Additionally, non-isolated CGs have a higher fraction of quenched galaxies relative to isolated CGs and the control sample. Based on our results, we propose an evolutionary scenario where the major structures in which the CGs are embedded accelerate the morphological transformations of their galaxy members, and also facilitates preprocessing. Our findings highlight the importance of considering the larger structures in which CGs may be located, when analysing the properties of their galaxy members, as this can significantly affect the evolution of CGs and their galaxies.