Radio recombination line forecasts with the Canadian Hydrogen Observatory and Radio-transient Detector (CHORD)

The Canadian Hydrogen Observatory and Radio-transient Detector (CHORD) is a 512-dish radio interferometer telescope under construction at the Dominion Radio Astrophysical Observatory (DRAO) near Penticton, British Columbia. This work estimates the capabilities of CHORD for detecting Radio Recombination Lines (RRLs) in the frequency range of 300-1500 MHz. This work analyzes the Radio Frequency Interference (RFI) present at DRAO and finds that 79 hydrogen Alpha RRL transitions are likely to be detectable. This work derives the theoretical sensitivity of CHORD to diffuse sources and explores the expected signal-to-noise gains by stacking multiple RRLs. We propose site locations to add additional dishes as part of Extension CHORD, and find that adding 32 dishes across two locations can improve angular resolution by 44% while decreasing sensitivity by 25%. Finally, we take published results of the Survey of Ionized Gas in the Galaxy Made with the Arecibo Telescope (SIGGMA), and estimate CHORD's detection capabilities given those results. We find that CHORD should have the sensitivity to match each of SIGGMA's detections using four observing days and can improve upon each SIGGMA detection in both sensitivity and angular resolution after 9 observing days.