Nanojanskylevel

Nanojanskylevel is an informal term used in radio astronomy to describe a sensitivity threshold corresponding to roughly one nanojansky (nJy) of flux density, i.e., 10^-9 Jy. It is not an SI unit but a practical benchmark for comparing the detectability of faint radio sources and the performance of telescopes and surveys.

The term blends nano- with the Jansky unit and the word level. It emerged in discussions around next-generation facilities such as the Square Kilometre Array (SKA) and the ngVLA, and is used to convey the scale of what is considered detectable rather than to specify a fixed measurement.

The nanojanskylevel is frequency- and setup-dependent. In practice, it depends on observing frequency, bandwidth, integration time, and array configuration. Radiometer-equation relations show that sensitivity ΔS scales with system temperature and effective collecting area, as ΔS ≈ 2 k T_sys / (A_eff sqrt(n_p Δν t)). Thus the nanojanskylevel is a target value achievable under a given observing plan.

Applications include planning deep-field surveys for faint extragalactic radio sources, studying diffuse emission, and experiments in 21-cm cosmology targeting the cosmic dawn.

Limitations include source confusion at low frequencies, calibration errors, and long integration times required. As an informal metric, reported nanojanskylevels can vary between instruments and observing strategies. Related concepts include the Jansky unit, the radiometer equation, and system-equivalent flux density used in radio astronomy sensitivity benchmarks.