Radial Velocities, Space Motions, and Nearby Young Moving Group Memberships of Eleven Candidate Young Brown Dwarfs

We present new radial velocity (RV) measurements for 11 candidate young very-low-mass stars and brown dwarfs, with spectral types from M7 to L7. Candidate young objects were identified by features indicative of low surface gravity in their optical and/or near-infrared spectra. RV measurements are derived from high-resolution (R = lambda/Delta lambda = 20,000) J-band spectra taken with NIRSPEC at the Keck Observatory. We combine RVs with proper motions and trigonometric distances to calculate three-dimensional space positions and motions and to evaluate membership probabilities for nearby young moving groups (NYMGs). We propose 2MASS J00452143+1634446 (L2 beta, J = 13.06) as an RV standard given the precision and stability of measurements from three different studies. We test the precision and accuracy of our RV measurements as a function of spectral type of the comparison object, finding that RV results are essentially indistinguishable even with differences of +/- 5 spectral subtypes. We also investigate the strengths of gravity-sensitive K I lines at 1.24-1.25 tm and evaluate their consistency with other age indicators. We confirm or reconfirm four brown dwarf members of NYMGs-2MASS J00452143+1634446, WISE J00470038+6803543, 2MASS J011747483403258, and 2MASS J193555952846343-and their previous age estimates. We identify one new brown dwarf member of the Carina-Near moving group, 2M2154-10. The remaining objects do not appear to be members of any known NYMGs, despite their spectral signatures of youth. These results add to the growing number of very-low-mass objects exhibiting signatures of youth that lack likely membership in a known NYMG, thereby compounding the mystery regarding local, low-density star formation.