The possiblity of detection of Ultracool Dwarfs with the UKIRT Infrared Deep Sky Survey

We present predictions for the numbers of ultra--cool dwarfs in the Galactic disk population that could be detected by the WFCAM/UKIDSS Large Area Survey and Ultra Deep Survey. Simulated samples of objects are created with masses and ages drawn from different mass functions and birthrates. Each object is then given absolute magnitudes in different passbands based on empirically derived bolometric correction vs. effective temperature relationships (or model predictions for Y dwarfs). These are then combined with simulated space positions, velocities and photometric errors to yield observables such as apparent magnitudes and proper motions. Such observables are then passed through the survey selection mechanism to yield histograms in colour. This technique also produces predictions for the proper motion histograms for ultra--cool dwarfs and estimated numbers for the as yet undetected Y dwarfs. Finally it is shown that these techniques could be used to constrain the ultra low--mass mass function and birthrate of the Galactic disk population