Detection of a large-scale stellar bar in the Milky Way

Abstract

This paper explores the structure of the stellar disk inside the solar circle using AGB star tracers. An algorithm for determining the lowest order harmonic terms of the stellar density distribution about the Galactic center is discussed. Using this algorithm, one sees strong evidence for a stellar bar with semimajor axis of about 5 kpc and position angle of -36 +/- 10 deg as seen from the sun-Galactic center line. The existence of the bar appears robust to uncertainties in the bolometric correction, amplitude of extinction, and the spread in intrinsic luminosity of the AGB stars. The maps also suggest the existence of spiral arms beginning at the ends of the inferred bar. The approach is easily adapted to more extensive surveys and large-scale components with different geometry.