Mapping the Asymmetric Thick Disk: A Search for Triaxilaity

Details Mapping the Asymmetric Thick Disk: A Search for Triaxilaity Mapping the Asymmetric Thick Disk: A Search for Triaxilaity

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.1416c&link_type=abstract

American Astronomical Society, AAS Meeting #211, #14.16; Bulletin of the American Astronomical Society, Vol. 39, p.761

Astronomy and Astrophysics

Astronomy

Scientific paper

Parker et al (2003, 2004) reported a significant spatial and kinematic asymmetry in the distribution of thick disk stars in the inner part of the Galaxy. In quadrant I, l ≈ 20 - 55° and 20 to 40° above and below the plane, there is an excess of 25% in the number of probable thick disk stars compared to the complementary fields (l = 340 - 305°) in quadrant IV. The region of this asymmetry covers several hundred square degrees and is therefore a major substructure in the Galaxy due to more than small-scale clumpiness. There is a corresponding kinematic signature; the stars showing the excess have a much slower rate of rotation (ω) with a lag of 80 - 90 km s-1 in the direction of Galactic rotation. Possible explanations for the spatial and kinematic asymmetry include the fossil remnant of a merger, a triaxial thick disk, and gravitational interaction with the stellar bar in the disk.
We have begun a program of photometric and spectroscopic observations to map the size and extent of this asymmetry along our line of sight. Our first results show that the spatial asymmetry in Q1 apparently does not extend to higher longitudes at fainter magnitudes. The star count ratios are 1 from l ≈ 55 to 75°. A triaxial thick disk is thus not a likely explanation for the asymmetry.

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