Approaches to High Dynamic Range Imaging - Application to the ngVLA

Abstract: The ngVLA is a new interferometric radio astronomy facility with transformative capabilities, being developed by the National Radio Astronomy Observatory. It combines two orders of magnitude in frequency coverage, over 1.2 - 116 GHz, with unprecedented sensitivity, spatial resolution and spatial frequency coverage, opening up new discovery space, impacting nearly every area of astrophysics. The high sensitivity that enables the path breaking science goals, which in turn lead to stringent instrument requirements, also open up new approaches to meeting them, previously only possible in limited contexts. Chief among the requirements are the image dynamic range specifications of 45 dB and 35 dB at 8 GHz and 27 GHz in single pointing and mosaiced observations. As the baseline calibration strategy to meet these requirements, we leverage the high ngVLA sensitivity through routine use of self-calibration on short time scales to counter atmospheric delay fluctuations and pointing self-calibration to correct for pointing errors. A key benefit of leveraging self-calibration techniques, where possible, is the a reduction in system complexity of a range of subsystems, which in turn improves system reliability. Self-calibration also promises the possibility of attaining thermal noise limited dynamic range performance in some cases. This presentation provides the bases for these approaches, illustrating them to make the case for their application to the ngVLA in parallel.