Description
Thanks to SKAO (Square Killometre Array Observatory) pathfinders, recent technological developments have allowed radio surveys to go deeper than ever before. One such example is the International LOFAR Telescope (ILT). The LOFAR Two-meter Sky Survey (LoTSS) Deep Field first data release provides us with 6” images at 144 MHz with sensitivities down to 20 μJy/beam using just the Dutch stations. This is just the beginning of what the ILT can achieve. Using Very Long Baseline Interferometry (VLBI) techniques, we can incorporate the international stations during the data reduction process, to produce sub-arcsecond resolution images.
Due to the ILT’s extensive field of view, we can produce widefield, high resolution images. These widefield images consist of billions of pixels and contain thousands of sources, each of which is at 0.3” resolution. However, this technique is challenging and very computationally expensive. To date, there are only two fully imaged fields, Lockman Hole and ELAIS-N1, at sub-arcsecond resolution (Sweijen et al. 2022, de Jong et al. 2024).
I will discuss the challenges that are faced when producing these images, including having to correct for differential ionospheric effects across multiple square degrees and starting self-calibration without knowing the source structure. I will present the first sub-arcsecond resolution image at 144 MHz of the Boötes Deep Field. Using this image, I will demonstrate the scientific potential of such widefield high resolution images.
The calibration knowledge gained by producing these images at such low frequencies will be critical or applying VLBI techniques to SKA-Low.
