A Comprehensive Investigation of Environmental Influences on Galaxies in Group Environments

TL;DR

This study investigates how group environments influence galaxy evolution, revealing that environmental factors pre-process star formation activity and that galaxy interactions vary with mass, affecting star formation efficiencies.

Contribution

It provides a comprehensive analysis of environmental effects on galaxy star formation, utilizing advanced visualization and a large, mass-complete galaxy sample up to z<0.1.

Findings

Star formation is pre-processed by group membership.

Quiescent galaxy fraction increases with group membership.

Close pairs show mass-dependent star formation enhancements or deficiencies.

Abstract

Environment has long been known to impact the evolution of galaxies, but disentangling its effects from mass evolution requires careful analysis of statistically significant samples. By implementing advanced visualisation methods to test group-finding algorithms, we utilise a mass-complete sample of galaxies to z < 0.1, comprising spectroscopic redshifts from prominent surveys such as the 2dFGRS and GAMA. Our group-finding methods identify 1,413 galaxy groups made up of 8,990 galaxies, corresponding to 36% of galaxies associated with group environments. We also search for close pairs, with separations of $r_{sep}$ < 50 h$^{-1}$ kpc and $v_{sep}$ < 500 km/s, and classify them into major ($M_{sec}/M_{prim} \leq$ 0.25) and minor ($M_{sec}/M_{prim}$ > 0.25) pairs. To examine the impact of environmental factors, we employ bespoke WISE photometry to derive a star-forming main sequence relation that shows star-formation (SF) within galaxies is pre-processed as a function of group membership. Our analysis reveals that SF in galaxies is pre-processed as a function of group membership. We observe an increase in the fraction of quiescent galaxies relative to the field as group membership rises, quantified using the environmental quenching efficiency metric ($\epsilon_{env}$). Within the star-forming population, we detect pre-processing with the relative difference in specific SF rates (${\Delta} sSFR$), showing a net decrease in SF as group membership increases, particularly at larger stellar masses. Our sample of close pairs at low stellar masses shows enhanced SF efficiencies compared to the field, while at larger masses, deficiencies are evident. Our results indicate that the small-scale environments of galaxies influence SF properties, demonstrating that galaxies do not evolve in isolation over cosmic time but are shaped by complex interactions between internal dynamics and external influences.