We present the results of a near-infrared ( NIR ) spectroscopic follow-up survey of 182 M4–L7 low-mass stars and brown dwarfs ( BDs ) from the BANYAN All-Sky Survey ( BASS ) for candidate members of nearby , young moving groups ( YMGs ) .
We confirm signs of low-gravity for 42 new BD discoveries with estimated masses between 8–75 M _ { \mathrm { Jup } } and identify previously unrecognized signs of low gravity for 24 known BDs .
This allows us to refine the fraction of low-gravity dwarfs in the high-probability BASS sample to \sim 82 % .
We use this unique sample of 66 young BDs , supplemented with 22 young BDs from the literature , to construct new empirical NIR absolute magnitude and color sequences for low-gravity BDs .
We show that low-resolution NIR spectroscopy alone can not differentiate between the ages of YMGs younger than \sim 120 Myr , and that the BT-Settl atmosphere models do not reproduce well the dust clouds in field or low-gravity L-type dwarfs .
We obtain a spectroscopic confirmation of low-gravity for 2MASS J14252798–3650229 , which is a new \sim 27 M _ { \mathrm { Jup } } , L4 \gamma bona fide member of AB Doradus .
We identify in this work a total of 19 new low-gravity candidate members of YMGs with estimated masses below 13 M _ { \mathrm { Jup } } , seven of which have kinematically estimated distances within 40 pc .
These objects will be valuable benchmarks for a detailed atmospheric characterization of planetary-mass objects with the next generation of instruments such as the James Webb Space Telescope .
We find 16 strong candidate members of the Tucana-Horologium association with estimated masses between 12.5–14 M _ { \mathrm { Jup } } , a regime where our study was particularly sensitive .
This would indicate that for this association there is at least one isolated object in this mass range for every 17.5 _ { -5.0 } ^ { +6.6 } main-sequence stellar member , a number significantly higher than expected based on standard log-normal initial mass function , however in the absence of radial velocity and parallax measurements for all of them , it is likely that this over-density is caused by a number of young interlopers from other moving groups .
Finally , as a byproduct of this project , we identify 12 new L0–L5 field BDs , seven of which display peculiar spectroscopic properties .