A new catalogue of polar-ring galaxies selected from the Sloan Digital Sky Survey★

Abstract

Galaxies with polar rings (PRGs) are a unique class of extragalactic objects. Using these, we can investigate a wide range of problems, linked to the formation and evolution of galaxies, and we can study the properties of their dark haloes. The progress that has been made in the study of PRGs has been constrained by the small number of known objects of this type. The Polar Ring Catalogue (PRC) by Whitmore et al. and their photographic atlas of PRGs and related objects includes 157 galaxies. At present, there are only about two dozen kinematically confirmed galaxies in this PRG class, mostly from the PRC.We present a new catalogue of PRGs, supplementing the PRC and significantly increasing the number of known candidate PRGs. The catalogue is based on the results of the original Galaxy Zoo project. Within this project, volunteers performed visual classifications of nearly a million galaxies from the Sloan Digital Sky Survey (SDSS). Based on the preliminary classifications of the Galaxy Zoo, we viewed more than 40 000 images of the SDSS and selected 275 galaxies to include in our catalogue.Our SDSS-based Polar Ring Catalogue (SPRC) contains 70 galaxies that we have classified as 'the best candidates'. Among these, we expect to have a very high proportion of true PRGs, and 115 good PRG candidates. There are 53 galaxies classified as PRG-related objects (mostly galaxies with strongly warped discs, and mergers). In addition, we have identified 37 galaxies that have their presumed polar rings strongly inclined to the line of sight (seen almost face-on). The SPRC objects are, on average, fainter and are located further away than the galaxies from the PRC, although our catalogue does include dozens of new nearby candidate PRGs.The SPRC significantly increases the number of genuine PRG candidates. It might serve as a good basis for both a further detailed study of individual galaxies and a statistical analysis of PRGs as a separate class of objects.We have performed spectroscopic observations of six galaxies from the SPRC at the 6-m Big Telescope Alt-Azimuthal (BTA). The existence of polar rings was confirmed in five galaxies, and one object appeared to be a projection of a pair of galaxies. Adding the data from the literature, we can already classify 10 galaxies from our catalogue as kinematically confirmed PRGs.

Star formation sustained by gas accretion

“…The central object is usually an early-type gas poor galaxy, but the ring itself is gas rich. Some galaxies have giant HI polar disks with very weak stellar counterpart (e.g., Moiseev et al 2011) expected from numerical simulations of minor mergers (e.g., Balcells and Quinn 1990;Immeli et al 2004); however, they also arise in hierarchical galaxy formation scenarios even in the absence of merging. Algorry et al (2014) model a disk galaxy fed by two distinct filamentary structures with opposite spins.…”

Disk heating and bending instability in galaxies with counterrotation

“…In such a picture, disk galaxies can be thought of as multispin systems (Rubin 1994;Conselice 2014). In some cases, rotation occurs in distinct planes or even in perpendicular planes, in configurations that sometimes contain structures that are usually called inner or outer polar rings (Whitmore et al 1987;Moiseev et al 2011;Moiseev 2012). These systems are interesting laboratories for the investigation of the dynamics of truly 3D matter distributions around galaxies (Sackett et al 1994;Combes & Arnaboldi 1996;Khoperskov et al 2014a).…”

Back to the Green Valley: How to Rejuvenate an S0 Galaxy through Minor Mergers

“…This is supported by the high fraction of S0 galaxies hosting both a ring and a bar (e.g., [6]). However, a resonance cannot be invoked for the outer polar rings (e.g., [7][8][9]), as well as for the most asymmetric and off-centre rings (e.g., [10]). …”