Characterising bars in low surface brightness galaxies

Abstract

In this paper, we use $\textit{B}$-band, $\textit{I}$-band, and 3.6 $\mu$m azimuthal light profiles of four low surface brightness (LSB) galaxies (UGC 628, F568-1, F568-3, F563-V2) to characterise three bar parameters: length, strength, and corotation radius. We employ three techniques to measure the radius of the bars, including a new method using the azimuthal light profiles. We find comparable bar radii between the $\textit{I}$-band and 3.6 $\mu$m for all four galaxies when using our azimuthal light profile method, and that our bar lengths are comparable to those in high surface brightness galaxies (HSBs). In addition, we find the bar strengths for our galaxies to be smaller than those for HSBs. Finally, we use Fourier transforms of the $\textit{B}$-band, $\textit{I}$-band, and 3.6 $\mu$m images to characterise the bars as either `fast' or `slow' by measuring the corotation radius via phase profiles. When using the $\textit{B}$ and $\textit{I}$-band phase crossings, we find three of our galaxies have faster than expected relative bar pattern speeds for galaxies expected to be embedded in centrally-dense cold dark matter haloes. When using the $\textit{B}$-band and 3.6 $\mu$m phase crossings, we find more ambiguous results, although the relative bar pattern speeds are still faster than expected. Since we find a very slow bar in F563-V2, we are confident that we are able to differentiate between fast and slow bars. Finally, we find no relation between bar strength and relative bar pattern speed when comparing our LSBs to HSBs.Comment: Accepted for publication in MNRAS, 25 pages, 36 figure