The bimodal initial mass function in the Orion nebula cloud

Due to its youth, proximity and richness the Orion Nebula Cloud (ONC) is an ideal testbed to obtain a comprehensive view on the Initial Mass Function (IMF) down to the planetary mass regime. Using the HAWK-I camera at the VLT, we have obtained an unprecedented deep and wide near-infrared JHK mosaic of the ONC (90% completeness at K ∼ 19.0mag, 22′×28′). Applying the most recent isochrones and accounting for the contamination of background stars and galaxies, we find that ONC’s IMF is bimodal with distinct peaks at about 0.25 and 0.025M separated by a pronounced dip at the hydrogen burning limit (0.08 M ), with a depth of about a factor 2–3 below the log-normal distribution. Apart from ∼920 lowmass stars (M 0.005M , hence about ten times more substellar candidates than known before. The substellar IMF peak at 0.025 M could be caused by BDs and IPMOs which have been ejected from multiple systems during the early star-formation process or from circumstellar disks.