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

TL;DR

This study used VLA radio observations of young stellar objects in Oph A to investigate disk dispersal mechanisms, finding limited evidence for UV-driven photoevaporation but leaving room for X-ray effects, and setting the stage for future SKA studies.

Contribution

First sensitive 10 GHz radio survey of YSOs in Oph A, analyzing emission mechanisms and constraining disk photoevaporation processes with implications for future SKA research.

Findings

Thermal dust emission contributes less than 30% at 10 GHz.

Non-detections of Class II/III disks suggest UV photoevaporation is insufficient.

X-ray photoevaporation remains a plausible disk dispersal mechanism.

Abstract

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.