  The determination of the lower-end of the initial mass function (IMF)
provides strong constraints on star formation theories. We report here on a
search for isolated planetary-mass objects in the 3 Myr-old star-forming region
IC 348. Deep, narrowband CH4off and CH4on images were obtained with CFHT/WIRCam
over 0.11 sq.deg. in the central part of IC 348 to identify young T-dwarfs from
their 1.6 um methane absorption bands. We report three faint T-dwarf candidates
with CH4on-CH4off colours > 0.4 mag. Extinction was estimated for each
candidate and lies in the range Av ~ 5-12 mag. Comparisons with T-dwarf
spectral models, and colour/colour and colour/magnitude diagrams, reject two of
the three candidates because of their extreme z' - J blueness. The one
remaining object is not thought to be a foreground field dwarf because of a
number density argument and also its strong extinction Av - 12 mag, or thought
to be a background field T-dwarf which would be expected to be much fainter.
Models and diagrams give this object a preliminary T6 spectral type. With a few
Jupiter masses, the young T-dwarf candidate reported here is potentially
amongst the youngest, lowest mass objects detected in a star-forming region so
far. Its frequency is consistent with the extrapolation of current lognormal
IMF estimates down to the planetary mass domain.
