Increasing the census of L and T dwarfs in wide binary and multiple systems using Dark Energy Survey DR1 and Gaia DR2 data

We present the discovery of 255 binary and six multiple system candidates with wide (> 5") separation composed by L or T dwarfs companions to stars, plus nine double brown dwarf systems. The sample of brown dwarf candidates was found in the Dark Energy Survey and the possible stellar companions are from Gaia DR2 and DES data. Our search is based in a common distance criterion with no proper motion information. For the Gaia DR2 stars we estimate distances based on their parallaxes and photometry, using the StarHorse code, while for DES stars, the StarHorse distances were purely photometric for the majority of cases, with a fraction having parallax measurement from Gaia DR2. L and T dwarfs distances are based on empirical templates ranging from L0 to T9. We also compute chance alignment probabilities in order to assess the physical nature of each pair. We find 174 possible pairs with Gaia DR2 primaries with chance alignment probabilities < 5%. We also find 85 binary pair candidates with a DES star as a primary, 81 of them with chance alignment probabilities < 5%. Only nine candidate systems composed of two brown dwarfs were identified. The sample of multiple systems is made up of five triple systems and one quadruple system. We determine that the typical wide binary fraction over the L and T spectral types is 2-4%. The significant leap provided by this sample will enable constraints on the formation and evolution of L and T dwarfs.