THE PATTERN SPEEDS OF NGC 3031, NGC 2366, AND DDO 154 AS FUNCTIONS OF RADIUS

Abstract

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