Intensity mapping with neutral hydrogen and the Hidden Valley simulations

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This paper introduces the Hidden Valley simulations, a set of trillion-particle N-body simulations in gigaparsec volumes aimed at intensity mapping science.

• We present details of the simulations and their convergence, then specialize to the study of 21-cm fluctuations between redshifts 2 and 6.
• Neutral hydrogen is assigned to halos using three prescriptions, and we investigate the clustering in real and redshift-space at the 2-point level.
• In common with earlier work we find the bias of HI increases from near 2 at z = 2 to 4 at z = 6, becoming more scale dependent at high z.