A Two-Hundred-Fifty-Six-Dish Array for 21-Centimetre Intensity Mapping: Thermal Noise and Baryon-Acoustic-Oscillation Significance Computed from the Survey Model

An intensity-mapping array for the redshifted 21-centimetre line of neutral hydrogen is designed from its thermal-noise budget. Two hundred fifty-six 6 m dishes with 50 K system temperature, observing 400 to 800 MHz, survey 15,000 square degrees in four years, spending 119,593 seconds per pointing and reaching a brightness-temperature noise of 0.10 mK per megahertz channel per pointing. Mode counting over the survey volume at the baryon-acoustic scale gives an aggregate detection significance of 51 sigma under the stated signal-to-noise model. The array totals 1,502 tonnes and 881 kW, the correlator dominating the power. All figures are computed from the stated survey model; the design is simulated, not measured.