The Tremaine-Weinberg method for pattern speeds using H-alpha emission from ionized gas

TL;DR

This study applies the Tremaine-Weinberg method to H-alpha emission data from ionized gas in nine nearby spiral galaxies, successfully measuring their pattern speeds and identifying multiple pattern speeds in some cases.

Contribution

It demonstrates the use of H-alpha emission with Fabry-Perot interferometry to measure galaxy pattern speeds using the Tremaine-Weinberg method, including detection of inner pattern speeds.

Findings

Linear pattern speeds were measured for all galaxies.

Two galaxies showed distinct inner pattern speeds with higher values.

The method proved effective with H-alpha emission data.

Abstract

The Fabry-Perot interferometer FaNTOmM was used at the 3.6m Canada France Hawaii Telescope and the 1.6m Mont Megantic Telescope to obtain data cubes in H-alpha of 9 nearby spiral galaxies from which maps in integrated intensity, velocity, and velocity dispersion were derived. We then applied the Tremaine-Weinberg method, in which the pattern speed can be deduced from its velocity field, by finding the integrated value of the mean velocity along a slit parallel to the major axis weighted by the intensity and divided by the weighted mean distance of the velocity points from the tangent point measured along the slit. The measured variables can be used either to make separate calculations of the pattern speed and derive a mean, or in a plot of one against the other for all the points on all slits, from which a best fit value can be derived. Linear fits were found for all the galaxies in the sample. For two galaxies a clearly separate inner pattern speed with a higher value, was also identified and measured.