Bar Strength and the Structure of Galaxies

University Of Alabama Tuscaloosa, Tuscaloosa AL

Investigators

Abstract

AST 0205143 Buta The principal objective of Dr. Ronald Buta's project is to use a new, direct technique for quantifying the strengths of bars in disk galaxies, and to derive the distribution of bar strengths in order to evaluate various scenarios for the origin of bars. The technique involves using near-infrared images to infer the gravitational potentials of galaxies, and then from these potentials estimating the actual torque due to the bar. The maximum value of the ratio of the tangential force to the mean radial force (called the relative bar torque parameter Qb) provides a single number that can characterize the bar strength of a whole galaxy. It is the most promising, direct technique for quantifying bar strength, and should supercede a host of other indirect methods that have been used in the past. Dr. Buta will refine the technique to improve its accuracy. A second objective of this project is to examine correlations between bar strength and other properties of galaxies, such as the shapes of bar dust lanes, chemical abundance gradients, the shapes and orientations of rings, the distribution of star formation, global star formation rates, nuclear activity, and bar ellipticity. These correlations are important because they allow us to understand how bars affect galaxy structure once they have formed. Secular evolution of structure is of critical importance in barred galaxies, and the role of bar strength on that evolution can be evaluated by studying these correlations. Measuring the distribution of bar strengths in galaxies is a critical piece of information that has not yet been used to constrain bar formation models. The origin of bars is a fundamental problem in astronomy. Through their nonaxisymmetric potentials, bars are thought to generate or at least influence the development of a host of phenomena including circumnuclear starbursts, bulge growth, global spiral structure, secondary bars, lenses, noncircular motions, and inner and outer rings. Bars are so pervasive, being found in at least 70% of disk galaxies, that they are clearly important to the structure and evolution of galaxies. Models can predict the distribution of expected Qb values for a given bar-formation scenario. ***