Ultracool dwarfs in Euclid Deep Fields

We also include UCDs identified by Gaia DR2. We selected seven UCD targets with different spectral types from the lists and obtained low-resolution 0.9-2.5um spectra of them using GTC/EMIR and the VLT/X-shooter. We also selected a young, bright L dwarf near EDF Fornax to test the coherence of these two facilities.

We included one extra T dwarf in EDF North with its published J-band spectrum. We retrieved a list of 81 (49, 231) M, eight (29, 115) L, and one (0, 2) T dwarf candidates in EDF North, Fornax, and South, respectively. They are provided to guide future UCD discoveries and characterisations by Euclid.

In total, we collected near-infrared spectra for nine UCDs, including two M types, three L types, and four T types in or close to the three EDFs. The Euclidised spectra show consistency in their spectral classification, which demonstrates that slitless Euclid spectroscopy will recover the spectral types with high fidelity for UCDs, both in the EDFs and in the wide survey. We also demonstrate that Euclid will be able to distinguish different age groups of UCDs.