A slow bar in a dark matter dominated galaxy

TL;DR

This study estimates the slow pattern speed of the bar in the dark matter dominated galaxy UGC 628 using the Tremaine-Weinberg method, revealing a slow bar likely influenced by dark matter dominance.

Contribution

First measurement of a slow bar pattern speed in a dark matter dominated galaxy using high-resolution Halpha data and the Tremaine-Weinberg method.

Findings

Bar pattern speed is among the lowest observed in spiral galaxies.

The bar's corotation radius ratio indicates a slow bar, beyond typical fast bar ranges.

Results suggest dark matter dominance influences bar dynamics.

Abstract

We report on an estimate of the bar pattern speed Omega_p for the low surface brightness spiral galaxy UGC 628. We applied the Tremaine-Weinberg method to high resolution Halpha velocity and integrated emission maps of this dark matter dominated galaxy. Observations were made at the CFHT using the optical Fabry-Perot interferometer, FaNTOmM. The Tremaine-Weinberg method estimates a bar pattern speed of (11.3 +/- 2.0) km/s/kpc for UGC 628, which is among the lowest values found for a spiral galaxy. The corotation radius Rc of the bar and the gaseous disc is Rc = 9.8 (+2.9/-2.0) kpc, implying a ratio R = Rc/Ab of 2.0 (+0.5/-0.3), where Ab is the bar radius. The ratio is well beyond the usual range of values, 1.0< R <1.4, found for fast bars of high surface brightness barred galaxies. It implies that the bar in UGC 628 is slow. As shown through the use of numerical simulations, fast bars survive when the inner mass distribution of galaxies is dominated by the baryons over the dark matter. Our result suggests that the presence of slow bars in galaxies is likely related to the dominance of dark matter over the mass distribution.