New young brown dwarfs in the Orion Molecular Cloud 2/3 region

Forty new low-mass members with spectral types ranging from M4 to M9 have been confirmed in the Orion Molecular Cloud (OMC) 2/3 region. Through deep, I-, z'-, J-, H-, and K-band photometry of a 20' x 20' field in OMC 2/3, we selected brown dwarf candidates for follow-up spectroscopy. Low-resolution far-red and near-infrared spectra were obtained for the candidates, and 19 young brown dwarfs in the OMC 2/3 region are confirmed. They exhibit spectral types of M6.5-M9, corresponding to approximate masses of 0.075-0.015 M-circle dot using the evolutionary models of Baraffe et al. At least one of these bona fide young brown dwarfs has strong H alpha emission, indicating that it is actively accreting. In addition, we confirm 21 new low-mass members with spectral types of M4-M6, corresponding to approximate masses of 0.35-0.10 M-circle dot in OMC 2/3. By comparing pre-main-sequence tracks to the positions of the members in the H-R diagram, we find that most of the brown dwarfs are less than 1 Myr, but find a number of low-mass stars with inferred ages greater than 3 Myr. The discrepancy in the stellar and substellar ages is due to our selection of only low-luminosity sources; however, the presence of such objects implies the presence of an age spread in the OMC 2/3 region. We discuss possible reasons for this apparent age spread.