PI: Jeffrey L. Carlin, University of Virginia, firstname.lastname@example.org
Address: Department of Astronomy, P. O. Box 400325, Charlottesville, VA 22904-4325, USA
CoI: Steven R. Majewski, University of Virginia
CoI: Ricardo R. Munoz, Yale University
Title: Fixing the Extragalactic Reference Frame For the Proper Motion of the Carina Dwarf Spheroidal
Abstract: \vskip -0.1in The orbital shapes of Milky Way dwarf spheroidal (dSph) galaxies provide specific constraints on CDM models of hierarchical structure formation on small scales and for late infalling subhalos. Furthermore, many physical properties of these dSph systems are shaped by tidal impulses, the magnitude of which depends on the orbit of the dSph. Unfortunately, the tangential (i.e., \it proper) motions of distant Milky Way dSphs are extremely difficult to measure, and thus remain poorly constrained (or in most cases unknown). We propose to remedy this for the Carina dSph, for which we have used a large, unique set of photographic plates spanning a 14 year baseline and covering large enough area to allow for a precise proper motion measurement. We have digitized these plates and derived precise (1-2 mas/yr per star) \it relative proper motions for 565 confirmed Carina members, and >1000 more likely members; these lead to a bulk relative proper motion for the system defined to 0.04 mas/yr. Despite this extreme precision, the \it absolute (relative to the ``fixed'' extragalactic background) proper motion of Carina is still poorly constrained, due to the paucity of identified QSOs (only 7) in the field of view to fix the reference frame. With our proposed search for QSOs among the ~2000 objects in our proper-motion catalog, we expect to discover ~50 QSOs, which will improve the accuracy of our proper motion zero point by a factor of 3 in each dimension, and likely more. This will allow for a precise determination of the orbit of the Carina dwarf galaxy, with an expected accuracy 2\times better than the recent proper motion for this object, which disagrees with the proper motion expected from the direction of Carina's tidal tails.
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