The Pattern Speeds of NGC 3031, NGC 2366, and DDO 154 as Functions of Radius

TL;DR

This study measures the pattern speeds of three galaxies using the Tremaine-Weinberg method, revealing variations with radius and differences from material speeds, and assessing the method's robustness across data qualities.

Contribution

It applies the Tremaine-Weinberg equations to multiple data sets of three galaxies, demonstrating the method's effectiveness and limitations in deriving radial pattern speed profiles.

Findings

NGC 3031's pattern speed aligns more with material speed.

NGC 2366 and DDO 154 show significant deviations from material speed.

Data resolution significantly impacts pattern speed measurements.

Abstract

The pattern speeds of NGC 3031, NGC 2366, and DDO 154 are measured using a solution of the Tremaine-Weinberg equations derived in a previous paper. Four different data sets of NGC 3031 produce consistent results despite differences in angular resolution, spectral resolution, and sensitivities to structures on different scales. The results for NGC 3031 show that the pattern speed is more similar to the material speed than it is to the speed of a rigidly rotating pattern, and that there are no clear indications of unique corotation or Lindblad resonances. Unlike NGC 3031, the results for NGC 2366 and DDO 154 show clear departures from the material speed. The results for NGC 2366 and DDO 154 also show that the solution method can produce meaningful results that are simple to interpret even if there is not a coherent or well-defined pattern in the data. The angular resolution of a data set has the greatest affect on the results, especially for determining the radial behavior of the pattern speed, and whether there is a single, global pattern speed.