The ultracool-field dwarf luminosity-function and space de nsity from the Canada-France Brown Dwarf Survey ?

Context. Thanks to recent and ongoing large scale surveys, hundreds of brown dwarfs have been discovered in the last decade. The Canada-France Brown Dwarf Survey is a wide-field survey for c ool brown dwarfs conducted with the MegaCam camera on the Canada-France-Hawaii Telescope telescope. Aims. Our objectives are to find ultracool brown dwarfs and to const rain the field brown-dwarf luminosity function and the mass function from a large and homogeneous sample of L and T dwarfs. Methods. We identify candidates in CFHT/MegaCam i 0 and z 0 images and follow them up with pointed near infrared (NIR) imaging on several telescopes. Halfway through our survey we found� 50 T dwarfs and� 170 L or ultra cool M dwarfs drawn from a larger sample of 1400 candidates with typical ultracool dwarfs i 0 − z 0 colours, found in 780 square degrees. Results. We have currently completed the NIR follow-up on a large part of the survey for all candidates from mid-L dwarfs down to the latest T dwarfs known with utracool dwarfs’ colours. T his allows us to draw on a complete and well defined sample of 10 2 ultracool dwarfs to investigate the luminosity function an d space density of field dwarfs. Conclusions. We found the density of late L5 to T0 dwarfs to be 2: 0 +0: 8 −0: 7 �10