We present the results of a search for cool white dwarfs in the United Kingdom InfraRed Telescope ( UKIRT ) Infrared Deep Sky Survey ( UKIDSS ) Large Area Survey ( LAS ) .
The UKIDSS LAS photometry was paired with the Sloan Digital Sky Survey ( SDSS ) to identify cool hydrogen-rich white dwarf candidates by their neutral optical colors and blue near-infrared colors , as well as faint Reduced Proper Motion magnitudes .
Optical spectroscopy was obtained at Gemini Observatory , and showed the majority of the candidates to be newly identified cool degenerates , with a small number of G- to K-type ( sub ) dwarf contaminants .
Our initial search of 280 deg ^ { 2 } of sky resulted in seven new white dwarfs with effective temperature T _ { eff } \approx 6000 K. The current followup of 1400 deg ^ { 2 } of sky has produced thirteen new white dwarfs .
Model fits to the photometry show that seven of the newly identified white dwarfs have 4120 K \leq T _ { eff } \leq 4480 K , and cooling ages between 7.3 Gyr and 8.7 Gyr ; they have 40 kms ^ { -1 } \leq v _ { tan } \leq 85 kms ^ { -1 } and are likely to be thick disk 10–11 Gyr-old objects .
The other half of the sample has 4610 K \leq T _ { eff } \leq 5260 K , cooling ages between 4.3 Gyr and 6.9 Gyr , and 60 kms ^ { -1 } \leq v _ { tan } \leq 100 kms ^ { -1 } .
These are either thin disk remnants with unusually high velocities , or lower-mass remnants of thick disk or halo late-F or G stars .