The hydrogen gas follows fluctuations in the underlying cosmic density field--regions where the 21cm emission is more intense correspond to regions where there is more matter--and so the intensity of the emission can be used to reconstruct the power spectrum of matter fluctuations.
The hydrogen gas follows fluctuations in the underlying cosmic density field--regions where the 21cm emission is more intense correspond to regions where there is more matter --. The intensity of the emission can be used to reconstruct the power spectrum of matter fluctuations.