Systematically Measuring Ultra-Diffuse Galaxies. VIII. Misfits, Miscasts, and Miscreants

TL;DR

This paper re-examines a large sample of ultra-diffuse galaxy candidates, classifies their morphologies, identifies interesting subtypes like mergers and ring galaxies, and discusses catalog contaminants to refine the list of genuine UDGs.

Contribution

It provides a detailed morphological classification and analysis of UDG candidates, highlighting new subtypes and catalog contaminants, improving the reliability of UDG identification.

Findings

Identification of merger sequences among UDGs

Discovery of dwarf ring galaxies possibly caused by polar collisions

Refinement of the UDG catalog by removing contaminants

Abstract

We re-examine the 7,070 candidate ultra-diffuse galaxies (UDGs) in the SMUDGes survey and provide classifications based on their visual morphology. Among the more interesting cases, we identify objects along a low surface brightness galaxy merger sequence (ongoing mergers (8) and post-mergers (7)) and a distinct set of dwarf ring galaxies (29). The ring galaxies are hypothesized to be the result of nearly polar-axis collisions, but the responsible companions are undetected. We also highlight objects in the catalog that appear to be tidally affected (66), thereby cautioning that their cataloged parameters may be unreliable. Finally, we identify contaminants of various types in the catalog, leaving 6,553 as viable undisturbed UDG candidates. We discuss all categories and provide example images of the more interesting ones.