Mapping the Asymmetric Thick Disk I. A Search for Triaxiality

Abstract

A significant asymmetry in the distribution of faint blue stars in the inner Galaxy, Quadrant 1 (l = 20 to 45 degrees) compared to Quadrant 4 was first reported by Larsen & Humphreys (1996). Parker et al (2003, 2004) greatly expanded the survey to determine its spatial extent and shape and the kinematics of the affected stars. This excess in the star counts was subsequently confirmed by Juric et al. (2008) using SDSS data. Possible explanations for the asymmetry include a merger remnant, a triaxial Thick Disk, and a possible interaction with the bar in the Disk. In this paper we describe our program of wide field photometry to map the asymmetry to fainter magnitudes and therefore larger distances. To search for the signature of triaxiality, we extended our survey to higher Galactic longitudes. We find no evidence for an excess of faint blue stars at l > 55 degrees including the faintest magnitude interval. The asymmetry and star count excess in Quadrant 1 is thus not due to a triaxial Thick Disk.

36 pages, 8 figures. Accepted by Astronomical Journal

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Cited by in corpus (5)

• The 3D Velocity Structure of the Thick Disk from SPM4 and RAVE DR2
• The Dark Energy Survey: Prospects for Resolved Stellar Populations
• A 10,000 star spectroscopic survey of the thick disk-halo interface : Phase-space sub-structure in the thick disk
• Mapping the Asymmetric Thick Disk: II Distance, Size and Mass of the Hercules Thick Disk Cloud
• Mapping the Asymmetric Thick Disk: III. The Kinematics and Interaction with the Galactic Bar