We report the first results of our ongoing campaign to discover the first
brown dwarfs (BD) in NGC 2264, a young (3 Myr), populous star forming region
for which our optical studies have revealed a very high density of potential
candidates - 236 in < 1 deg2 - from the substellar limit down to at least
∼ 20 MJup​ for zero reddening. Candidate BD were first selected
using wide field (I,z) band imaging with CFH12K, by reference to current
theoretical isochrones. Subsequently, 79 (33%) of the I,z sample were found
to have near-infrared 2MASS photometry (JHKs​± 0.3 mag. or better),
yielding dereddened magnitudes and allowing further investigation by comparison
with the location of NextGen and DUSTY isochrones in colour-colour and
colour-magnitude diagrams involving various combinations of I,J,H and
Ks​. We discuss the status and potential substellarity of a number of
relatively unreddened (Av​< 5) likely low-mass members in our
sample, but in spite of the depth of our observations in I,z, we are as yet
unable to unambiguously identify substellar candidates using only 2MASS data.
Nevertheless, there are excellent arguments for considering two faint (observed
I∼ 18.4 and 21.2) objects as cluster candidates with masses
respectively at or rather below the hydrogen burning limit. More current
candidates could be proven to be cluster members with masses around 0.1
M⊙​ {\it via} gravity-sensitive spectroscopy, and deeper near-infrared
imaging will surely reveal a hitherto unknown population of young brown dwarfs
in this region, accessible to the next generation of deep near-infrared
surveys.Comment: 10 pages, 12 figures, accepted by A&