The Catalog of Southern Ringed Galaxies

Abstract

The Catalog of Southern Ringed Galaxies (CSRG) is a comprehensive compilation of diameters, axis ratios, relative bar position angles, and morphologies of inner and outer rings, pseudorings, and lenses in 3692 galaxies south of declination - 17^deg^. The purpose of the catalog is to evaluate the idea that these ring phenomena are related to orbital resonances with a bar or oval in galaxy potentials. The catalog is based on visual inspection of most of the 606 fields of the Science Research Council (SRC) IIIa-J southern sky survey, with the ESO-B, ESO-R, and Palomar Sky surveys used as auxiliaries when needed for overexposed core regions. The catalog is most complete for SRC fields 1-303 (mostly south of declination -42^deg^). In addition to ringed galaxies, a list of 859 mostly nonringed galaxies intended for comparison with other catalogs is provided. Detailed analysis of 5403 duplicate estimates of ring diameters (D) and 1606 duplicate estimates of bar/ring position angles (θ) indicates that the CSRG has very good internal precision and homogeneity in these parameters. For an "average" ring or lens of angular diameter 0.6' and apparent axis ratio 0.8, the internal errors are σ(D) = 0.026' and σ(θ) = 6.3^deg^. Based on a comparison with two other major sources of ring-diameter measurements, the external mean error in CSRG diameters is ~3.2 times the internal error at a given diameter. Comparison of the type classifications with those in other catalogs indicates good agreement on interpretations of features, including family and variety. Improved model distributions of apparent axis ratios and bar/ring position angles are computed which allow for the errors in the observed parameters and the fact that most of the observed rings have small angular diameters. These model distributions use Gaussian intrinsic distributions of shapes and angles, and contain the fundamental assumption that the spin axes are randomly oriented to the line of sight. Comparison with observed distributions is accomplished using the x^2^ test. The results are consistent with my previous 1986 analysis, but are much stronger because the samples are larger and better defined and the analysis is more thorough. The full CSRG confirms the noncircular average intrinsic shapes of galaxy rings, pseudorings, and lenses. The typical outer feature has an intrinsic axis ratio of 0.87 +/- 0.14, while the typical inner feature has an intrinsic axis ratio of 0.84 +/- 0.10. Weak dependences on family (i.e., apparent bar strength) are found, with SB features being more elongated than SA features. Similar results, but with smaller best-fitting dispersions, are found from an identical analysis of the completely independent set of ring axis ratio measurements from the Southern Galaxy Catalogue of Corwin, de Vaucouleurs, & de Vaucouleurs (1985). The distribution of bar/ring position angles shows once again that outer features have two preferred intrinsic alignment angles with respect to bars (parallel and perpendicular), while inner features have one preferred intrinsic alignment angle (parallel). Most outer features in SB galaxies are aligned perpendicular to the bar, while most outer features in SAB galaxies are aligned parallel to the bar. The perpendicular and parallel varieties of outer features are readily distinguished morphologically in many galaxies as the R'_1_ and R'_2_ subclasses, respectively. These findings again link the observed ring features to specific orbital resonances with a bar or oval. Outer features are very likely tracers of the location of the outer Lindblad resonance, while inner features are very likely tracers of the location of an ultraharmonic resonance near and inside corotation. These firm identifications allow the possibility for indirect measurement of the bar pattern speed in many galaxies. Other findings from the CSRG that are not based on statistics are the identification of intrinsic bar/ring misalignment; bars which underfill inner rings; dimpling of R'_1_ pseudorings; pointy, rectangular, or hexagonal inner or outer ring shapes: a peculiar polar-ring-related system; and other extreme examples of spiral structure and ring morphology.