2009MNRAS.395.1631L

We present the discovery of two brown dwarfs in the UK infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Deep Extragalactic Survey (DXS) Data Release 2 (DR2). Both objects were selected photometrically from 6deg² in DXS for their blue J - K colour and the lack of optical counterparts in the Sloan Digital Sky Survey (SDSS) Stripe 82. Additional optical photometry provided by the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) corroborated the possible substellarity of these candidates. Subsequent methane imaging of UDXS J221611.51+003308.1 and UDXS J221903.10+002418.2 has confirmed them as T7±1 and T6±1 dwarfs at photometric distances of 81 (52-118 pc) and 60 (44-87 pc; 2σ confidence level). A similar search in the DR2 of the Ultra-Deep Survey over a smaller area (0.77deg²) and shallower depth did not return any late-T dwarf candidate. The numbers of late-T dwarfs in our study are broadly in line with a declining mass function when considering the current area and depth of the DXS and UDS. These brown dwarfs are the first discovered in the Visible Imaging Multi-Object Spectrograph (VIMOS) 4 field and among the few T dwarfs found in pencil-beam surveys. They are valuable to investigate the scaleheight of T dwarfs.