The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is a radio telescope array that will map nearly all of the southern sky in radio continuum and neutral hydrogen line emission over a frequency range of 400 to 800 MHz. The primary goal of HIRAX is to use 21-cm intensity mapping to measure baryon acoustic oscillations (BAOs): these are remnant ripples in the distribution of galaxies that are imprinted by primordial sound waves that existed in the early universe. The characteristic BAO length scale can be used as a “ruler” for charting the expansion history of the universe and for shedding light on the nature of dark energy. HIRAX science goals include the following:
HIRAX will be an interferometer that comprises roughly 1000 six-meter dishes placed in a close-packed, redundant configuration, and will be deployed at the SKA site in the Karoo desert in South Africa. The operating frequency of 400-800 MHz corresponds to a redshift range of 0.8 to 2.5. The dishes will be stationary and will have a 5-10 degree field of view, and the dishes will be periodically repointed in elevation in order to build up coverage of the southern sky. HIRAX is highly complementary to the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and will share much of the back-end technology, including FPGA-based ICE boards and the GPU correlator.