COUGS-DESI: A Catalog of Unusual Galaxies with Polar Structures in the DESI Legacy Imaging Surveys

TL;DR

This paper presents COUGS-DESI, the largest catalog of polar-structure galaxies identified in DESI Legacy Imaging Surveys, enabling extensive statistical analysis of their properties and occurrence in the local universe.

Contribution

The study constructs the most comprehensive and homogeneous catalog of PSGs using advanced classification methods, significantly expanding the known sample size.

Findings

Catalog contains 2,989 PSG candidates, including 342 known objects.

Projection effects are negligible, confirming catalog reliability.

Polar rings are present in about 0.7% of local non-dwarf galaxies.

Abstract

Polar-structure galaxies (PSGs) host photometrically and kinematically decoupled components oriented at large angles to one another. These systems, which include polar rings, polar disks, polar halos, polar bulges, polar dust lanes, and polar tidal structures, provide valuable insights into galaxy formation and evolution, although their rarity has limited statistical studies. We aim to construct the largest and most homogeneous catalog of PSGs to date in order to enable robust statistical studies of their properties and occurrence rates in the local Universe. Using DESI Legacy Imaging Surveys (DR10) data, we identified PSG candidates in the Siena Galaxy Atlas (SGA) through visual inspection, convolutional neural network classification, and cross-matching with previously reported systems. Each galaxy was assigned a PSG subtype and host morphology. We analyzed general properties of PSGs and compared them with those for all galaxies in the SGA. Simple image simulations were used to evaluate projection effects. The resulting Catalog of Unusual Galaxies with polar Structures in the DESI Legacy Imaging Surveys (COUGS-DESI) contains 2,989 PSG candidates, including 342 previously known objects. Projection effects from random galaxy overlaps are negligible. The sample spans a wide range of polar morphologies, with 1,113 polar rings, 75 polar bulges, 216 polar halos, 185 polar dust lanes, and 1,315 polar tidal structures. PSGs constitute 2.2% of local non-dwarf galaxies, with polar rings representing 0.7%. Approximately 1% of S0 galaxies in the SGA host polar rings, whereas spirals constitute the most common morphological type among the PSG hosts in our catalog. COUGS--DESI increases the number of known PSG candidates by an order of magnitude and provides a foundation for detailed studies of the formation and evolution of polar structures.