Near term measurements with 21 cm intensity mapping: neutral hydrogen fraction and BAO at z<2

Understand

It is shown that 21 cm intensity mapping could be used in the near term to make cosmologically useful measurements.

• Large scale structure could be detected using existing radio telescopes, or using prototypes for dedicated redshift survey telescopes.
• This would provide a measure of the mean neutral hydrogen density, using redshift space distortions to break the degeneracy with the linear bias.
• We find that with only 200 hours of observing time on the Green Bank Telescope, the neutral hydrogen density could be measured to 25% precision at redshift 0.54<z<1.09.