# The environment of HI-bearing ultra diffuse galaxies in the ALFALFA survey

## TL;DR

This study investigates the environments of HI-bearing ultra diffuse galaxies (HUDs) from the ALFALFA survey, finding they inhabit similar environments as other HI galaxies, suggesting internal processes drive their properties.

## Contribution

It provides the first comprehensive environmental analysis of a large sample of HUDs, showing their distribution is environment-independent, challenging external influence theories.

## Key findings

- HUDs share environments with other HI-selected galaxies
- No environmental preference observed for HUDs
- Internal mechanisms likely drive HUD properties

## Abstract

We explore the environment of 252 HI-bearing Ultra Diffuse Galaxies (HUDs) from the 100% ALFALFA survey catalog in an attempt to constrain their formation mechanism. We select sources from ALFALFA with surface brightnesses, magnitudes, and radii consistent with other samples of Ultra Diffuse Galaxies (UDGs), without restrictions on their isolation or environment, more than doubling the previously reported ALFALFA sample. We quantify the galactic environment of HUDs using several metrics, including n-th nearest neighbour, tidal influence, membership in a group/cluster, and distance from nearest group/cluster or filament. We find that that HUDs inhabit the same environments as other samples of HI-selected galaxies and that they show no environmental preference in any metric. We suggest that these results are consistent with a picture of the extreme properties of HUDs being driven by internal mechanisms and that they are largely unperturbed by environmental impacts. While environmental effects may be necessary to convert HUDs into gas-poor cluster UDGs, these effects are not required for diffuse galaxies to exist in the first place.