The initial mass function in the Rho Ophiuchi cluster

Approximately 20 sq arcmin in the Rho Ophiuchi cloud were imaged deeply at 2.2 microns. No new sources were found down to a completeness limit of m(k) = 14.5. Either the low-mass sources have radically different infrared spectra than higher mass ones, or the initial mass function levels out or turns over near a few tenths of a solar mass, and the formation of very low mass stars and substellar objects is suppressed. If this later results is true generally, large substellar objects cannot contribute significantly to the 'missing mass'.