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

TL;DR

This paper reports the discovery and confirmation of two distant T-type brown dwarfs in the UKIDSS Deep Extragalactic Survey, providing insights into the population and distribution of such objects.

Contribution

First identification of T7 and T6 brown dwarfs in the UKIDSS DXS data, confirming their substellar nature through methane imaging and analyzing their implications for the brown dwarf population.

Findings

Confirmed two T7±1 and T6±1 brown dwarfs at ~60-80 pc

No late-T dwarfs found in a smaller, shallower survey area

Results align with a declining brown dwarf mass function

Abstract

We present the discovery of two brown dwarfs in the UKIRT Infrared Deep Sky Survey (UKIDSS) Deep Extragalactic Survey (DXS) Data Release 2. Both objects were selected photometrically from six square degrees 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 (CFHT-LS) 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$\pm$1 and T6$\pm$1 dwarfs at photometric distances of 81 (52-118 pc) and 60 (44-87 pc; 2 sigma confidence level). A similar search in the second data release of the Ultra Deep Survey over a smaller area (0.77 square degree) and shallower depth didn't 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 VIMOS 4 field and among the few T dwarfs found in pencil-beam surveys. They are valuable to investigate the scale height of T dwarfs.