  We have observed 6 late-L and T dwarfs with the Karl G. Jansky Very Large
Array (VLA) to investigate the presence of highly circularly polarized radio
emission, associated with large-scale auroral currents. Previous surveys
encompassing ~60 L6 or later targets in this spectral range have yielded only
one detection. Our sample includes the previously detected T6.5 dwarf 2MASS
10475385+2124234 as well as 5 new targets selected for the presence of H-alpha
emission or optical/infrared photometric variability, which are possible
manifestations of auroral activity. We detect 2MASS 10475385+2124234, as well
as 4 of the 5 targets in our biased sample, including the strong IR variable
SIMP J01365662+0933473 and bright H-alpha emitter 2MASS 12373919+6526148,
reinforcing the possibility that activity at these disparate wavelengths is
related. The radio emission frequency corresponds to a precise determination of
the lower-bound magnetic field strength near the surface of each dwarf and this
new sample provides robust constraints on dynamo theory in the low mass brown
dwarf regime. Magnetic fields >2.5 kG are confirmed for 5/6 targets. Our
results provide tentative evidence that the dynamo operating in this mass
regime may be inconsistent with predicted values from a recently proposed
model. Further observations at higher radio frequencies are essential for
verifying this assertion.
