The Suppression of Star Formation and the Effect of Galaxy Environment in Low-Redshift Galaxy Groups

TL;DR

This study uses GALEX data to analyze how galaxy group environments suppress star formation in member galaxies, revealing that both local and global factors contribute to quenching processes over timescales of around 2 billion years.

Contribution

It provides the first direct evidence of specific star formation rate suppression within group galaxies and highlights the combined role of tidal interactions and starvation in quenching.

Findings

Star formation is suppressed in group galaxies compared to the field.

Specific star formation rate is reduced by about 40% in group galaxies.

Galaxy groups contribute significantly to the universe's UV emission.

Abstract

Understanding the interaction between galaxies and their surroundings is central to building a coherent picture of galaxy evolution. Here we use GALEX imaging of a statistically representative sample of 23 galaxy groups at z=0.06 to explore how local and global group environment affect the UV properties and dust-corrected star formation rates of their member galaxies. The data provide star formation rates out to beyond 2R_200 in all groups, down to a completeness limit and limiting galaxy stellar mass of 0.06 M_sun/yr and 10^8 M_sun, respectively. At fixed galaxy stellar mass, we find that the fraction of star-forming group members is suppressed relative to the field out to an average radius of R ~ 1.5 Mpc ~ 2R_200, mirroring results for massive clusters. For the first time we also report a similar suppression of the specific star formation rate within such galaxies, on average by 40% relative to the field, thus directly revealing the impact of the group environment in quenching star formation within infalling galaxies. At fixed galaxy density and stellar mass, this suppression is stronger in more massive groups, implying that both local and global group environment play a role in quenching. The results favor an average quenching timescale of at least ~2 Gyr and strongly suggest that a combination of tidal interactions and starvation is responsible. Despite their past and ongoing quenching, galaxy groups with more than four members still account for at least ~25% of the total UV output in the nearby universe.