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We performed a HST/WFC3-IR imaging survey of the young stellar cluster NGC2024 in three filters probing the 1.4~$\mu$m H$_2$O absorption feature,characteristic of the population of low mass and sub-stellar mass objects downto a few Jupyter masses. We detect 812 point sources, 550 of them in all 3filters with signal to noise greater than 5. Using a distance-independenttwo-color diagram we determine extinction values as high as $A_V\simeq 40$. Wealso find that the change of effective wavelengths in our filters results inhigher $A_V$ values as the reddening increases. Reconstructing a dereddenedcolor-magnitude diagram we derive a luminosity histogram for both the fullsample of candidate cluster members and for an extinction-limited sub-samplecontaining the 50% of sources with $A_V\lesssim 15$. Assuming a standardextinction law like Cardelli et al. (1989) with a nominal $R_V$=3.1 we producea luminosity function in good agreement with the one resulting from aSalpeter-like Initial Mass Function for a 1~Myr isochrone. There is someevidence of an excess of luminous stars in the most embedded region. We positthat the correlation may be due to those sources being younger, and thereforeoverluminous than the more evolved and less extinct cluster's stars. We compareour classification scheme based on the depth of the 1.4$\mu$m photometricfeature with the results from the spectroscopic survey of Levine et al. (2006),and we report a few peculiar sources and morphological features typical of therich phenomenology commonly encountered in young star-forming regions.

A HST Study of the Substellar Population of NGC 2024