Auroral radio emission from late L and T dwarfs: A new constraint on dynamo theory in the substellar regime

TL;DR

This study detects auroral radio emissions from late L and T dwarfs, providing new constraints on magnetic dynamo theories in substellar objects by measuring magnetic field strengths and comparing them with theoretical predictions.

Contribution

It presents the first robust detections of radio emissions from a biased sample of late L and T dwarfs, offering empirical constraints on dynamo models in the substellar regime.

Findings

Magnetic fields >2.5 kG confirmed in 5 out of 6 targets

Radio detections correlate with H-alpha emission and infrared variability

Results challenge existing dynamo models for low-mass brown dwarfs

Abstract

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.