VLA cm-wave survey of young stellar objects in the Oph A cluster:
  constraining extreme UV- and X-ray-driven disk photo-evaporation -- A
  pathfinder for Square Kilometre Array studies
  Observations of young stellar objects (YSOs) in centimeter bands can probe
the continuum emission from growing dust grains, ionized winds, and
magnetospheric activity, which are intimately connected to the evolution of
protoplanetary disks and the formation of planets. We have carried out
sensitive continuum observations toward the Ophiuchus A star-forming region
using the Karl G. Jansky Very Large Array (VLA) at 10 GHz over a field-of-view
of 6$'$ with a spatial resolution of $\theta_{maj}$ $\times$ $\theta_{min}$
$\sim$ 0.4$''$ $\times$ 0.2$''$. We achieved a 5 $\mu$Jy beam$^{-1}$
root-mean-square noise level at the center of our mosaic field of view. Among
the eighteen sources we detected, sixteen are YSOs (three Class 0, five Class
I, six Class II, and two Class III) and two are extragalactic candidates. We
find that thermal dust emission generally contributes less that 30% of the
emission at 10 GHz. The radio emission is dominated by other types of emission
such as gyro-synchrotron radiation from active magnetospheres, free-free
emission from thermal jets, free-free emission from the outflowing
photo-evaporated disk material, and/or synchrotron emission from accelerated
cosmic-rays in jet or protostellar surface shocks. These different types of
emission could not be clearly disentangled. Our non-detections towards Class
II/III disks suggest that extreme UV-driven photoevaporation is insufficient to
explain the disk dispersal, assuming that the contribution of UV
photoevaporating stellar winds to radio flux does not evolve with time. The
sensitivity of our data cannot exclude photoevaporation due to X-ray photons as
an efficient mechanism for disk dispersal. Deeper surveys with the Square
Kilometre Array will be able to provide strong constraints on disk
photoevaporation.
