Using the Tremaine-Weinberg method to measure pattern speeds from H\alpha velocity maps

TL;DR

This paper adapts the Tremaine-Weinberg method to H-alpha velocity maps from Fabry-Perot data cubes to measure spiral galaxy pattern speeds, addressing emission discontinuities and validating results through simulations and corotation comparisons.

Contribution

It introduces a novel application of the Tremaine-Weinberg method to H-alpha data cubes, overcoming emission discontinuity issues and validating pattern speed measurements.

Findings

Pattern speeds are consistent with corotation radii and bar lengths.

Simulations support the credibility of the measured pattern speeds.

Method provides a new way to analyze galaxy dynamics using H-alpha data.

Abstract

The Tremaine-Weinberg method is a well-known model independent technique for measuring density wave pattern speeds in spiral galaxies. Here we show how it can be applied to the data cubes (maps of surface brightness and velocity) obtained in H-alpha emission using a Fabry-Perot spectrometer. One of the main difficulties, the discontinuity of the H-alpha emission, is resolved using the neighbouring stellar continuum delivered by the data cube. We argue from symmetry that the motions not associated with the density wave should cancel. We show that our pattern speeds are reasonable by computing corotation radii, and comparing them to measured bar lengths. Simulations including star forming gas also add credibility to our results. Nevertheless it will be necessary to compare them with results using the spectra of the stellar components to quantify any systematic deviations from valid pattern speed values.