New Young Brown Dwarfs in the Orion Molecular Cloud 2/3 Region

TL;DR

This study identifies and confirms 40 new low-mass members, including young brown dwarfs, in the Orion Molecular Cloud 2/3 region through photometry and spectroscopy, revealing an age spread among these objects.

Contribution

The paper reports the discovery and spectroscopic confirmation of 40 new low-mass members, including brown dwarfs, in OMC 2/3, and discusses their age distribution and implications.

Findings

Confirmed 19 young brown dwarfs with spectral types M6.5-M9.

Identified 21 low-mass stars with spectral types M4-M6.

Most brown dwarfs are less than 1 Myr old, with some older objects indicating an age spread.

Abstract

Forty new low mass members with spectral types ranging from M4-M9 have been confirmed in the Orion Molecular Cloud 2/3 region. Through deep, I, z', J, H, K 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_solar using the evolutionary models of Baraffe et al. (1998). At least one of these bona fide young brown dwarfs has strong Halpha 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_solar 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.