The polar ring galaxy AM1934-563 revisited

TL;DR

This study presents spectroscopic observations of the polar-ring galaxy AM1934-563, revealing detailed rotation curves and a dwarf galaxy companion, and discusses possible formation scenarios including merger and cold gas accretion.

Contribution

It provides new spectroscopic data on AM1934-563, including rotation curves and the discovery of a dwarf galaxy, offering insights into its formation mechanisms.

Findings

Rotation curves extend to 8 kpc for gas and stars.

Identification of a dwarf HII galaxy as part of the group.

Discussion of merger versus cold gas accretion scenarios.

Abstract

We report long-slit spectroscopic observations of the dust-lane polar-ring galaxy AM1934-563 obtained with the Southern African Large Telescope (SALT) during its performance-verification phase. The observations target the spectral region of the Ha, [NII] and [SII] emission-lines, but show also deep NaI stellar absorption lines that we interpret as produced by stars in the galaxy. We derive rotation curves along the major axis of the galaxy that extend out to about 8 kpc from the center for both the gaseous and the stellar components, using the emission and absorption lines. We derive similar rotation curves along the major axis of the polar ring and point out differences between these and the ones of the main galaxy. We identify a small diffuse object visible only in Ha emission and with a low velocity dispersion as a dwarf HII galaxy and argue that it is probably metal-poor. Its velocity indicates that it is a fourth member of the galaxy group in which AM1934-563 belongs. We discuss the observations in the context of the proposal that the object is the result of a major merger and point out some observational discrepancies from this explanation. We argue that an alternative scenario that could better fit the observations may be the slow accretion of cold intergalactic gas, focused by a dense filament of galaxies in which this object is embedded (abridged).