The Low-Mass Initial Mass Function in the Orion Nebula Cluster Based on HST/NICMOS III Imaging

We present deep HST/NICMOS Camera 3 F110W and F160W imaging of a 26 × 33 arcmin^2 , corresponding to 3.1 pc × 3.8 pc, non-contiguous field towards the Orion Nebula Cluster. The main aim is to determine the ratio of low-mass stars (0.08 - 1 M ) to brown dwarfs (0.03 - 0.08 Msun) for the cluster as a function of radius out to a radial distance 1.5 pc. The ratio found for the cluster within a radius of 1.5 pc is R03 = N(0.08 ∼ ?Msun)/N(0.03 ∼ (0.08Msun) = 2.4 ± 0.2, after correcting for field stars. The ratio for the central 0.3 pc × 0.3 pc region down to 0.03 Msun was previously found to be R03 = 3.3+0.8-0.7, suggesting the low-mass content of the cluster is mass segregated.