Direct measurements of bar pattern speeds

TL;DR

This paper discusses the measurement of bar pattern speeds in barred galaxies, focusing on the Tremaine-Weinberg method, its limitations, and efforts to extend its application to different galaxy types.

Contribution

It reviews the uncertainties in current measurement techniques and explores extending the Tremaine-Weinberg method to gaseous components for broader applicability.

Findings

Most bars rotate near their corotation radius.

Direct and indirect methods yield consistent results.

Efforts are underway to reduce measurement biases.

Abstract

The dynamics of a barred galaxy depends on the angular velocity or pattern speed of its bar. Indeed, it is related to the location of corotation where gravitational and centrifugal forces cancel out in the rest frame of the bar. The only direct method for measuring the bar pattern speed is the Tremaine-Weinberg technique. This method is best suited to the analysis of the distribution and kinematics of the stellar component in absence of significant star formation and patchy dust obscuration. Therefore, it has been mostly used for early-type barred galaxies. The main sources of uncertainties on the directly-measured bar pattern speeds are discussed. There are attempts to overcome the selection bias of the current sample of direct measurements by extending the application of the Tremaine-Weinberg method to the gaseous component. Furthermore, there is a variety of indirect methods which are based on the analysis of the gas distribution and kinematics. They have been largely used to measure the bar pattern speed in late-type barred galaxies. Nearly all the bars measured with direct and indirect methods end close to their corotation radius, i.e., they are as rapidly rotating as they can be.