Faint Blue Objects in the Hubble Deep Field-South Revealed: White Dwarfs, Subdwarfs, and Quasars

We explore the nature of the faint blue objects in the Hubble Deep Field-South. We have derived proper motions for the point sources in the Hubble Deep Field-South using a 3 yr baseline. Combining our proper-motion measurements with spectral energy distribution fitting enabled us to identify four quasars and 42 stars, including three white dwarf candidates. Two of these white dwarf candidates, HDF-S 1444 and 895, are found to display significant proper motion, 21.1 ± 7.9 and 34.9 ± 8.0 mas yr-1, and are consistent with being thick-disk or halo white dwarfs located at ~2 kpc. The other faint blue objects analyzed by Mendez & Minniti do not show any significant proper motion and are inconsistent with being halo white dwarfs; they do not contribute to the Galactic dark matter. The observed population of stars and white dwarfs is consistent with standard Galactic models.