MAPPING THE ASYMMETRIC THICK DISK. I. A SEARCH FOR TRIAXIALITY

摘要

A significant asymmetry in the distribution of faint blue stars in the inner Galaxy, Quadrant 1 (1 = 20°-45°)compared to Quadrant 4 was first reported by Larsen Humphreys in 1996. Parker et al. greatly expanded thesurvey to determine its spatial extent and shape and the kinematics of the affected stars. This excess in the starcounts was subsequently confirmed by Jurie et al. using Sloan Digital Sky Survey data. Possible explanationsfor the asymmetry include a merger remnant, a triaxial thick disk, and a possible interaction with the bar inthe disk. In this paper, we describe our program of wide field photometry to map the asymmetry to faintermagnitudes and therefore larger distances. To search for the signature of triaxiality, we extended our survey tohigher Galactic longitudes. We find no evidence for an excess of faint blue stars at 1 55° including the faintestmagnitude interval. The asymmetry and star count excess in Quadrant 1 is thus not due to a triaxial thick disk.