Compact groups of galaxies in GAMA -- Probing the densest minor systems at intermediate redshifts

TL;DR

This study constructs large, reliable samples of compact galaxy groups at intermediate redshifts using GAMA and SDSS data, revealing their properties and role in galaxy evolution, especially star formation suppression due to interactions.

Contribution

The paper introduces new, extensive samples of compact galaxy groups at intermediate redshifts, enabling detailed analysis of their properties and environmental effects beyond the local universe.

Findings

Compact groups have a higher fraction of quenched galaxies than loose groups.

Embedded compact groups show the highest compactness and brightest first-ranked galaxies.

No significant evolution of compact group properties with redshift.

Abstract

[Abridged] Over the years, several compact group catalogues have been built using different methods, but most of them are not deep enough to go beyond the very local universe with a high level of redshift completeness. We build statistically reliable samples of compact groups to study the influence of their inner extreme environment at intermediate redshifts. We adopted the GAMA redshift survey as a parent catalogue, complemented with galaxies from the SDSS, to identify compact groups using Hickson-like criteria. We explored the parameter space to perform several identifications: we reduced the maximum galaxy separation in the line-of-sight to 500 km/s and we implemented different magnitude ranges to define membership. For comparison, we used control samples extracted from a catalogue of loose groups to contrast properties with the compact groups. We build five considerably large compact group samples, ranging from more than 400 up to ~2400 systems, and maximum redshifts from 0.2 to 0.4. The overall properties of each sample are in agreement with previous findings. Compact groups tend to have a larger fraction of quenched galaxies than control loose groups, mainly for low stellar mass galaxies in compact groups with small crossing times. In addition, ~45% of compact groups are embedded in loose galaxy systems and display the highest compactness, lowest crossing times and brightest first-ranked galaxies compared to compact groups considered non-embedded or isolated. There is almost no evolution of compact group properties with redshift. Our results confirm previous findings that postulate compact groups as one of the suitable places to study the suppression of the star formation rate in galaxies primarily due to galaxy interactions. These new samples will be valuable to deepen the analysis of these peculiar galaxy systems in a redshift regime poorly explored so far.