An HI View of Galaxy Conformity: HI-rich Environment around HI-excess Galaxies

TL;DR

This study reveals that HI-rich spiral galaxies tend to have an excess of neutral hydrogen in their surrounding environment, suggesting they accrete gas from extended reservoirs, which impacts galaxy evolution.

Contribution

It demonstrates a statistical connection between galaxy HI content and environmental HI mass, highlighting the role of extended gas reservoirs in galaxy growth.

Findings

HI-rich galaxies have excess environmental HI mass

Environmental HI consists of undetected gas clumps

Galaxies may accrete gas from their surroundings

Abstract

Using data taken as part of the Bluedisk project we study the connection between neutral hydrogen (HI) in the environment of spiral galaxies and that in the galaxies themselves. We measure the total HI mass present in the environment in a statistical way by studying the distribution of noise peaks in the HI data cubes obtained for 40 galaxies observed with WSRT. We find that galaxies whose HI mass fraction is high relative to standard scaling relations have an excess HI mass in the surrounding environment as well. Gas in the environment consists of gas clumps which are individually below the detection limit of our HI data. These clumps may be hosted by small satellite galaxies and\or be the high-density peaks of a more diffuse gas distribution in the inter-galactic medium. We interpret this result as an indication for a picture in which the HI-rich central galaxies accrete gas from an extended gas reservoir present in their environment.