Foreground and RFI Mitigation with the Baryon Mapping experiment (BMX)

Understanding the nature of Dark Energy is one of the primary unanswered questions in cosmology, and was identified as one of the Department of Energy’s current five priority science missions. In order to measure the effects of Dark Energy and constrain its equation of state, it is necessary to map the expansion history of the universe over a broad range of redshifts. A number of optical instruments designed to map the Large Scale Structure (LSS) of the universe including DES, DESI, and the Vera Rubin Observatory have begun observing, and are expected to produce critical constraints in this field. Intensity Mapping (IM) is also emerging as a potentially complementary method of mapping the LSS of the universe, by using integrated line emissions as tracers of structure. In particular, 21 -cm IM would use the hyperfine "spin flip" transition of neutral hydrogen, which is present throughout cosmic time and as a significant fraction of the baryonic mass of the universe, as a tracer of LSS. Several radio interferometers are already observing, or under development, to measure 21-cm emissions from different redshift ranges, and planning is underway for second generation Stage II experiments.