Only the Lonely: H I Imaging of Void Galaxies

TL;DR

This study presents HI imaging of 15 void galaxies, revealing their gas-rich, dynamic nature, interactions, and ongoing accretion, providing insights into galaxy evolution in underdense cosmic environments.

Contribution

First HI imaging survey of a purely environmentally selected sample of void galaxies, revealing their gas content, interactions, and kinematic features in low-density regions.

Findings

Void galaxies are gas-rich and dynamically active.

Many galaxies show signs of interactions and perturbed HI disks.

Presence of previously unidentified companions and polar HI disks.

Abstract

Void galaxies, residing within the deepest underdensities of the Cosmic Web, present an ideal population for the study of galaxy formation and evolution in an environment undisturbed by the complex processes modifying galaxies in clusters and groups, as well as provide an observational test for theories of cosmological structure formation. We have completed a pilot survey for the HI imaging aspects of a new Void Galaxy Survey (VGS), imaging 15 void galaxies in HI in local (d < 100 Mpc) voids. HI masses range from 3.5 x 10^8 to 3.8 x 10^9 M_sun, with one nondetection with an upper limit of 2.1 x 10^8 M_sun. Our galaxies were selected using a structural and geometric technique to produce a sample that is purely environmentally selected and uniformly represents the void galaxy population. In addition, we use a powerful new backend of the Westerbork Synthesis Radio Telescope that allows us to probe a large volume around each targeted galaxy, simultaneously providing an environmentally constrained sample of fore- and background control sample of galaxies while still resolving individual galaxy kinematics and detecting faint companions in HI. This small sample makes up a surprisingly interesting collection of perturbed and interacting galaxies, all with small stellar disks. Four galaxies have significantly perturbed HI disks, five have previously unidentified companions at distances ranging from 50 to 200 kpc, two are in interacting systems, and one was found to have a polar HI disk. Our initial findings suggest void galaxies are a gas-rich, dynamic population which present evidence of ongoing gas accretion, major and minor interactions, and filamentary alignment despite the surrounding underdense environment.