Galaxy transmutations: The double ringed galaxy ESO 474-G26

Abstract

Surface photometry and a 21 cm H i line spectrum of the giant double-ringed galaxy ESO 474-G26 are presented. The morphology of this system is unique among the 30 000 galaxies with 155. Two almost orthogonal optical rings with diameters of 60 and 40 kpc surround the central body (assuming km s-1 Mpc-1). The outer one is an equatorial ring, while the inner ring lies in a nearly polar plane. The rings have blue optical colors typical of late-type spirals. Both appear to be rotating around the central galaxy, so that this system can be considered as a kinematically confirmed polar ring galaxy. Its observational characteristics are typical of galaxy merger remnants. Although the central object has a surface brightness distribution typical of elliptical galaxies, it has a higher surface brightness for its effective radius than ordinary ellipticals. Possible origins of this galaxy are discussed and numerical simulations are presented that illustrate the formation of the two rings in the merging process of two spiral galaxies, in which the observed appearance of ESO 474-G26 appears to be a transient stage.