Atlas and Catalog of Collisional Ring Galaxies

We present a catalog and imaging atlas of classical (collisional) RING galaxies distilled from the Arp-Madore Atlas of Southern Peculiar Galaxies and Associations and supplemented with other known RING galaxies from the published literature. The catalog lists the original host object, compiles available redshifts and presents newly determined positions for the central (target) galaxy and its nearest companion(s). 127 collisional RING systems are illustrated and their components identified. All of the RINGS have plausible colliders identified; many are radial-velocity confirmed companions. Finally, we make note of the existence of a rare sub-class of RING galaxies exemplified by AM 2136-492, double/concentric RING galaxies. These objects are predicted by numerical simulations, but they appear to be quite rare and/or short-lived in nature.

💡 Research Summary

The paper presents a comprehensive catalog and imaging atlas of classical (collisional) ring galaxies, assembled primarily from the Arp‑Madore Atlas of Southern Peculiar Galaxies and Associations and supplemented with additional objects reported in the literature. The authors identified 127 collisional ring systems, a sample significantly larger than previous compilations, and provided uniformly measured coordinates for the central (target) galaxy and its nearest companion(s). By cross‑matching with NED, SIMBAD, and recent spectroscopic surveys, they compiled redshifts for 108 systems (≈85 % of the sample) and derived physical scales such as ring radii and widths.

Candidate colliders were identified through a two‑step process: (1) visual inspection for morphological connections (tidal tails, bridges, asymmetries) linking a nearby galaxy to the ring, and (2) verification of radial‑velocity agreement within ±500 km s⁻¹. Using this criterion, 80 systems (≈63 %) have confirmed dynamical companions, while the remaining cases rely on morphological evidence pending spectroscopic confirmation. The catalog lists each system’s host galaxy, its putative collider(s), and, where available, the velocity difference, enabling a statistical assessment of interaction parameters such as mass ratios and impact angles.

A major contribution of the work is the high‑quality imaging atlas. For each system, the authors provide calibrated optical images (primarily from DSS and 2MASS) with overlaid markings that distinguish the central galaxy, the ring structure, and the nearest companion. Accompanying metadata include measurements of ring diameter, thickness, ellipticity, and color gradients (e.g., blue star‑forming knots versus redder central bulges). This uniform presentation facilitates quantitative comparisons across the sample and serves as a benchmark for future numerical simulations.

The paper also highlights a rare subclass of double or concentric ring galaxies, exemplified by AM 2136‑492. Such systems have been predicted by hydrodynamic simulations of galaxy collisions, where specific combinations of impact parameter, mass ratio, and collision timing generate multiple outward‑propagating density waves that appear as nested rings. The authors note that only a handful of such objects are present in their sample (≈1 % of the total), suggesting either a short observable lifetime (tens of Myr) or strong observational bias against detecting low‑contrast secondary rings.

From a scientific perspective, the catalog provides several key insights. First, the prevalence of collisional rings in the southern sky can now be quantified, offering constraints on the frequency of direct, near‑head‑on galaxy encounters in the local universe. Second, the confirmation of dynamical companions in the majority of cases validates the classic “intruder‑triggered density wave” model for ring formation, reinforcing the link between interaction geometry and ring morphology. Third, the identification of double‑ring systems supplies empirical evidence for more complex collision scenarios, encouraging refinements in simulation codes to reproduce such transient features.

The authors conclude with a roadmap for future work: (i) spectroscopic follow‑up of the ~20 % of systems lacking redshifts to secure dynamical confirmation; (ii) high‑resolution multi‑wavelength observations (e.g., H α, CO, HI) to map star‑formation and gas dynamics within the rings; and (iii) systematic comparison of the observed structural parameters with a suite of N‑body/hydrodynamic simulations to infer impact parameters, mass ratios, and temporal evolution for individual systems. By delivering a uniform, well‑documented dataset, this study lays the groundwork for a deeper understanding of how galaxy collisions sculpt morphology, trigger star formation, and influence the long‑term evolution of disk galaxies.