Two distant brown dwarfs in the UKIRT Infrared Deep Sky Survey Deep Extragalactic Survey Data Release 2

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 6 deg² in DXS for their blue <i>J</i> − <i>K</i> 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 (0.77 deg²) 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.