Radio continuum emission from knots in the DG Tau jet
  Context: HH 158, the jet from the young star DG Tau, is one of the few
sources of its type where jet knots have been detected at optical and X-ray
wavelengths. Aims: To search, using Very Large Array observations of this
source, radio knots and if detected, compare them with the optical and X-ray
knots. To model the emission from the radio knots. Methods: We analyzed archive
data and also obtained new Very Large Array observations of this source, as
well as an optical image, to measure the present position of the knots. We also
modeled the radio emission from the knots in terms of shocks in a jet with
intrinsically time-dependent ejection velocities. Results: We detected radio
knots in the 1996.98 and 2009.62 VLA data. These radio knots are,within error,
coincident with optical knots. We also modeled satisfactorily the observed
radio flux densities as shock features from a jet with intrinsic variability.
All the observed radio, optical, and X-ray knot positions can be intepreted as
four successive knots, ejected with a period of 4.80 years and traveling away
from the source with a velocity of 198 km s$^{-1}$ in the plane of the sky.
Conclusions: The radio and optical knots are spatially correlated and our model
can explain the observed radio flux densities. However, the X-ray knots do not
appear to have optical or radio counterparts and their nature remains poorly
understood.
