A Catalog of 531 White Dwarf Candidates in the Local Galactic Halo from Gaia Data Release 2

Abstract

We present a catalog of 531 white dwarf candidates that have large apparent transverse motions relative to the Sun ($v_{T} > 200$ km s$^{-1}$), thus making them likely members of the local Galactic halo population. The candidates were selected from the Gaia Data Release 2, and are located in a great circle with $20^\circ$ width running across both Galactic poles and Galactic center and anti-center, a zone that spans 17.3% of the sky. The selection used a combination of kinematic and photometric properties, derived primarily from Gaia proper motions, $G$ magnitudes, and $G_{{\rm BP}}\,-\,G_{{\rm RP}}$ color, and including parallax whenever available. Additional validation of the white dwarf candidates is made using PanSTARRS photometric ($gri$) data. Our final catalog includes not only stars having full kinematic and luminosity estimates from reliable Gaia parallax, but also stars with presently unreliable or no available Gaia parallax measurements. We argue that our method to select local halo objects with and without reliable parallax data leads us to rounding up all possible halo white dwarfs in the Gaia catalog (in that particular section of that sky) with recorded proper motions $> 40$ mas yr$^{-1}$, and that pass our $v_{T} > 200$ km s$^{-1}$ threshold requirement. We expect this catalog will be useful for the study of the white dwarf population of the local Galactic halo.