# xGASS: Gas-rich central galaxies in small groups and their connections to cosmic web gas feeding

## TL;DR

This study reveals that low-mass central galaxies in small groups have higher atomic hydrogen content and star formation rates than isolated counterparts, likely due to cosmic web accretion or minor mergers, with no difference at higher masses.

## Contribution

It provides new insights into how environment influences cold gas content and star formation in central galaxies, highlighting the role of cosmic web feeding at low masses.

## Key findings

- Low-mass group centrals have ~0.3 dex higher HI gas fractions than isolated ones.
- Higher gas content correlates with increased star formation and molecular hydrogen in low-mass centrals.
- No significant difference in gas content or star formation at higher stellar masses.

## Abstract

We use deep HI observations obtained as part of the extended GALEX Arecibo SDSS survey (xGASS) to study the cold gas properties of central galaxies across environments. We find that, below stellar masses of 10^10.2 Msun, central galaxies in groups have an average atomic hydrogen gas fraction ~0.3dex higher than those in isolation at the same stellar mass. At these stellar masses, group central galaxies are usually found in small groups of N=2 members. The higher HI content in these low mass group central galaxies is mirrored by their higher average star formation activity and molecular hydrogen content. At larger stellar masses, this difference disappears and central galaxies in groups have similar (or even smaller) gas reservoirs and star formation activity compared to those in isolation. We discuss possible scenarios able to explain our findings and suggest that the higher gas content in low mass group central galaxies is likely due to contributions from the cosmic web or HI-rich minor mergers, which also fuel their enhanced star formation activity.