Polar disk galaxy found in wall between voids

TL;DR

A unique polar disk galaxy was discovered in a cosmological wall between voids, showing signs of recent cold gas accretion and providing insights into galaxy formation in underdense environments.

Contribution

This is the first serendipitous discovery of an isolated polar disk galaxy in a void wall with detailed HI observations supporting cold flow accretion theories.

Findings

HI mass comparable to stellar mass in the galaxy

Evidence of a warp in the outer HI disk

Gas accretion from voids inferred from galaxy orientation

Abstract

We have found an isolated polar disk galaxy in what appears to be a cosmological wall situated between two voids. This void galaxy is unique as its polar disk was discovered serendipitously in an HI survey of SDSS void galaxies, with no optical counterpart to the HI polar disk. Yet the HI mass in the disk is comparable to the stellar mass in the galaxy. This suggests slow accretion of the HI material at a relatively recent time. There is also a hint of a warp in the outer parts of the HI disk. The central, stellar disk appears relatively blue, with faint near UV emission, and is oriented (roughly) parallel to the surrounding wall, implying gas accretion from out of the voids. The considerable gas mass and apparent lack of stars in the polar disk, coupled with the general underdensity of the environment, supports recent theories of cold flow accretion as an alternate formation mechanism for polar disk galaxies.