Feasibility of Self-Calibration for ngVLA Dynamic Range Requirements

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. We recognize the broader nature of the problem - requiring a certain dynamic range, DR, at a targeted science noise level σ_science presupposes the presence of bright emission in the field at a corresponding level of detected interferometric flux of \sim DR \times σ_science, by definition. With the problem posed broadly in this way, one can derive a general limit without recourse to background source counts and the attendant Poisson fluctuations of their occurrence, and which depends only on the number of antennas in the array and the science noise level of the observation, independent of the observing band, primary beam size and antenna SEFDs. This memo formally explores these ideas as the main strategy to achieve the ngVLA image dynamic range requirements.