AM 1934-563: a giant spiral polar-ring galaxy in a triplet

¹ Astronomical Institute of St. Petersburg State University, 198504 St. Petersburg, Russia e-mail: resh@astro.spbu.ru
² Observatoire de Paris, LERMA, 61 Av. de l'Observatoire, 75014 Paris, France
³ Isaac Newton Institute of Chile, St. Petersburg Branch
⁴ MCT/Laboratório Nacional de Astrofísica, Caixa Postal 21, CEP:37.504-364, Itajubá, MG, Brasil

Received: 26 July 2004
Accepted: 15 September 2005

Abstract

We have observed the emission-line kinematics and photometry of a southern triplet of galaxies. The triplet contains a giant spiral galaxy AM 1934-563 whose optical structure resembles a polar-ring galaxy: a distorted spiral disk, seen almost edge-on, and a faint large-scale (45 kpc in diameter) warped structure, inclined by 60°–70° with respect to the disk major axis. The triplet shows a relatively small velocity dispersion (69 km s^-1) and a large crossing time (0.17 in units of the Hubble time). The disk of AM 1934-563 demonstrates optical colors typical of early-type spirals, a strong radial color gradient, and almost exponential surface brightness distribution with an exponential scale-length value of 3.1 kpc (R passband). The galaxy shows a maximum rotation velocity of about 200 km s^-1 and it lies close to the Tully-Fisher relation for spiral galaxies. The suspected polar ring is faint () and strongly warped. Its total luminosity comprises 10-15% of the total luminosity of AM 1934-563. We model this system using numerical simulations, and study its possible formation mechanisms. We find that the most robust model that reproduces the observed characteristics of the ring and the host galaxy is the tidal transfer of mass from a massive gas-rich donor galaxy to the polar ring. The physical properties of the triplet of galaxies are in agreement with this scenario.