The global environment of small galaxy systems

Abstract

ABSTRACT The main goal of this work is to investigate the influence of environment at different scales on the properties of galaxies in systems with a low number of members. To this end, we used a catalogue of small galaxy systems comprising compact and locally isolated pairs, triplets, and groups with four and up to six galaxies. We consider fixed aperture estimators and found that at scales lower than 5 ${\ \rm Mpc}$ pairs are associated to lower density environments than triplets and groups. Moreover, a nearest neighbour approach highlights that triplets prefer denser environments than pairs and slightly less dense environments than groups. When considering the position within the cosmic web we found that pairs and triplets in our sample are associated to void environments while galaxy groups are more likely to reside in void walls. In agreement with these results, the system-galaxy cross-correlation function shows that pairs inhabit environments of lesser density compared to triplets and groups, and on small scales ($\lt\! 3{\ \rm Mpc}$) triplets appear to behave as an intermediate system. Related to the properties of neighbour galaxies of small systems we found that the neighbours of groups present a lower fractions of star-forming, young stellar population, and blue colour galaxies with respect to neighbours of triplet and pair systems. These results suggest that differences in the properties of galaxies in pairs, triplets, and groups are not only related to the existence of an extra galaxy member but also to the large-scale environment inhabited by the systems.