Halo White Dwarfs, Thick Disks and a Sanity Check

The discovery of a population of high proper motion white dwarfs by Oppenheimer et al (2001) has caused a lot of speculation as to the origin of these stars. I show that the age distribution of the white dwarfs offers a kind of sanity check in these discussions. In particular, this population appears to have a similar age distribution to those in the standard, thin disk white dwarf population. This is not what is expected for either the halo or thick disk, which are thought to be old populations. It may indicate a different dynamical origin entirely, or it may be just be the tail of a larger distribution, implying a significantly larger total density in even older white dwarfs.