Constraining the nature of DG Tau A's thermal and non-thermal radio emission

DG Tau A, a class-II YSO known to drive a radio/optical, bipolar jet, is associated with both thermal, and non-thermal, radio emission. To investigate the nature of this emission, we present JVLA 6 and 10 GHz observations with resolutions of 3.1" and 1.9" respectively. Image noise levels range between 1.7 and 2.7 uJy/beam, making these the most sensitive radio observations of this target to date. No polarization is detected towards DG Tau A, or its associated radio knots, A, C and D with 3-sigma upper limits on the degree of linear polarization of <1.3, <50.8, <18.2 and <51.5% respectively. Over 3.81 yr, no proper motions are observed towards the non-thermal radio knot C, previously thought to be a bowshock. Its quasi-static nature, spatially resolved variability and offset from the central jet axis supports a scenario whereby it is instead a stationary shock driven into the surrounding medium by the jet. Towards the internal working surface, knot A, we derive an absolute velocity of 258+/-23 km/s, after correcting for inclination, using our measured proper motion and those of other works. A spatially-resolved flux density increase of the red-shifted jet of DG Tau A is also seen, indicating that the receding jet has probably undergone a variable mass loss event, the first time such an event has been observed in the counter-jet. For this ejection we measure a diameter of 101+/-34 au and, if optically thin, this indicates an ionised mass loss rate of (3.7+/-1.0) x 10^-8 solar masses per year during the event. Since we do not see a contemporaneous ejection in the approaching jet, we conclude it to be an asymmetric process. Finally, using radiative transfer modelling towards a power-law defined jet model, we find that the extent of the radio emission can only be explained with the presence of shocks, and therefore reionisation, in the flow.