Measuring Radially Varying Pattern Speeds in Spiral Galaxies

University Of New Mexico, Albuquerque NM

Investigators

Abstract

Dr. Rand and graduate student Sharon Meidt will apply a new method to measure how fast the spiral and bar patterns of disk galaxies rotate about the galaxy center. These patterns are found in most disk galaxies, including our own Milky Way. Classical theories of spiral structure posit that an unstable disk of stars develops a set of growing modes, each with a fixed pattern speed. Structures with multiple pattern speeds, interpreted as coupled modes, have been seen in gravitational N-body simulations of galaxy disks; generally, the faster pattern dominates closer to the center. Dr Rand and collaborator Michael Merrifield have developed the 'modified Tremaine-Weinberg' method to test whether observed spiral galaxies also have multiple pattern speeds. This method will be applied to seven nearby spiral galaxies for which the velocity field has been well mapped in CO and neutral hydrogen gas. This method will directly measure of the pattern speed to test theoretical models for the formation of spiral structure, and to determine whether the spirals are winding up over time. The University of New Mexico is both a research university and a Hispanic-serving institution. The work will form the PhD thesis of a woman graduate student.