A Space-Based Observational Strategy for Characterizing the First Stars and Galaxies Using the Redshifted 21-cm Global Spectrum

Understand

The redshifted 21-cm monopole is expected to be a powerful probe of the epoch of the first stars and galaxies ($10<z<35$).

• The global 21-cm signal is sensitive to the thermal and ionization state of hydrogen gas and thus provides a tracer of sources of energetic photons -- primarily hot stars and accreting black holes -- which ionize and heat the high redshift intergalactic medium (IGM).
• This paper presents a strategy for observations of the global spectrum with a realizable instrument placed in a low altitude lunar orbit, performing night-time 40-120 MHz spectral observations, while on the farside to avoid terrestrial radio frequency interference, ionospheric corruption, and solar radio emissions.
• The frequency structure, uniformity over large scales, and unpolarized state of the redshifted 21-cm spectrum are distinct from the spectrally featureless, spatially-varying, and polarized emission from the bright foregrounds.