VLITE Observations of the Hubble Ultra Deep Field

Abstract

We present 136 hr of 340 MHz observations of the Hubble Ultra Deep Field (HUDF) conducted with the VLA Low-band Ionosphere and Transient Experiment (VLITE), collected commensally with higher-frequency Karl G. Jansky Very Large Array (VLA) observations. Our deepest image combines 20 hr of data, covers 4 square degrees, and achieves an angular resolution of 8.8 arcsec x 3.8 arcsec with an rms sensitivity of 158 microJy per beam at the field center. We catalog 671 radio sources detected above 5 sigma significance. Correcting for incompleteness using injection-recovery simulations with a model radio continuum population, we show that our source counts recover the sub-mJy star-forming galaxy population at abundances consistent with other deep fields at comparable frequencies. The data span 45 observing days across two VLA A-configuration semesters separated by 1.3 years, providing a search for variability on ~1-year timescales at sub-mJy flux densities. We identify eleven variable sources with flux densities of 1-100 mJy and modulation indices of 6-40%, six of which exhibit peaked radio spectra consistent with compact AGN. Their variability amplitudes are consistent with refractive interstellar scintillation (RISS) predicted for this line of sight, though three sources with modulation indices exceeding 30% likely require an intrinsic contribution. One source, subsequently confirmed as a compact symmetric object through VLBA follow-up observations, demonstrates the potential of VLITE for identifying populations of young radio AGN through commensal low-frequency variability searches.