Ultracool dwarfs in ALHAMBRA and COSMOS

We complement ALHAMBRA and COSMOS photometry with other catalogues in the optical and infrared using VOSA, a VO tool that estimates effective temperatures from the spectral energy distribution fitting to collections of theoretical models. The agreement between the number of UCDs found in the COSMOS field and theoretical estimations together with the low false-negative rate (known UCDs not discovered in our search) validates the methodology proposed in this work, which will be used in the forthcoming wide and deep surveys provided by the Euclid space mission.

Simulations of Euclid number counts for UCDs detectable in different photometric passbands are presented for a wide survey area of 15000deg^2^, and the limitations of applicability of Euclid data to detect UCDs using the methods employed in this paper are discussed.