We have cross-correlated the 2dF QSO Redshift Survey ( 2QZ ) white dwarf catalog with the GALEX 2nd Data Release and the Sloan Digital Sky Survey ( SDSS ) data release 5 to obtain ultraviolet photometry ( FUV , NUV ) for approximately 700 objects and optical photometry ( ugriz ) for approximately 800 objects .
We have compared the optical-ultraviolet colors to synthetic white dwarf colors to obtain temperature estimates for approximately 250 of these objects .
These white dwarfs have effective temperatures ranging from 10 000 K ( cooling age of about 1Gyr ) up to about 40 000 K ( cooling age of about 3 Myrs ) , with a few that have even higher temperatures .
We found that to distinguish white dwarfs from other stellar luminosity classes both optical and ultraviolet colors are necessary , in particular for the hotter objects where there is contamination from B and O main-sequence stars .
Using this sample we build a luminosity function for the DA white dwarfs with M _ { V } < 12 mag .