The polar ring galaxy AM1934-563 revisited

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).Comment: 19 pages, 13 figures, submitted to MNRAS. Some figures were bitmapped to reduce the size. Full resolution version is available from http://www.saao.ac.za/~akniazev/pub/AM1934_563.pd

On the nature of the apparent ring galaxy SDSS J075234.33+292049.8

“…In contrast to the situation regarding spiral galaxies, as shown by van Zee et al (1998) as well as by Denicoló, Terlevich & Terlevich (2002), very few PRGs have been studied to determine their metal abundances. A few examples are UGC 5600 (Shalyapina, Moiseev & Yakovleva 2002) where no gradient was found, NGC 7468 (Shalyapina et al 2004) with an inverted gradient where the outer parts are more metal‐rich than the inner parts, and AM1934‐563 (Brosch et al 2007) with a normal gradient for the galaxy but a constant metallicity for the ring.…”

“…The study of PRGs may, therefore, be beneficial also to the investigation of the nature of the DM in galactic haloes. This was demonstrated by the Southern African Large Telescope (SALT) observations of the PRG AM1934−563 (Brosch et al 2007) where the DM halo appears to have collapsed onto the luminous part of the galaxy, not onto the ring.…”

A Pair of Leading Spiral Arms in a Luminous Infrared Galaxy?

“…With the link to interactions and tidal disturbances and a way to probe the DM halo, leading arms are cousins of other intriguing and rare effects in disk galaxies, such as counterrotating disks and (polar) rings (Tremaine & Yu 2000;Vergani et al 2007;Brosch et al 2007). To understand spiral galaxy evolution, and to answer the questions above, more modeling and more and new kinds of observations are needed.…”

African Eyes on the Sky: The Southern African Large Telescope

“…Brosch et al 2007, Väisänen et al 2008, Kniazev et al 2008. Results from these were encouraging considering the throughput shortfall of the spectrograph and the image quality of the whole telescope at the time and much mire is expected with the repaired system.…”