The H i–halo mass relation at redshift z ∼ 1 from the Minkowski functionals of 21-cm intensity maps

Abstract

ABSTRACT The mean and the scatter of the H i content of a dark matter halo as a function of the halo mass are useful statistics that can be used to test models of structure and galaxy formation. We investigate the possibility of constraining this H i–halo mass relation (HIHMR) from intensity maps of the redshifted 21-cm line. In particular, we use the geometry and topology of the brightness-temperature isocontours in a single frequency channel as quantified by the Minkowski functionals. First, we generate mock maps from a large N-body simulation considering the impact of thermal noise and foreground removal. We then use the Fisher information formalism to forecast constraints on a parametric model for the HIHMR. We consider a 20 000 deg2 survey (originally proposed for dark energy science) conducted with the Square Kilometre Array Phase 1 (SKA-1) MID observatory operating in single-dish mode. For a channel bandwidth of 2 MHz, we show that an integration time of a few$\, \times \, 10^4$ s per pointing is sufficient to image the smoothed H i distribution at redshift z ≃ 1 and to measure the HIHMR in a nearly optimal way from the Minkowski functionals. Tighter constraints on some of the parameters can be obtained by using also an independent measurement of the mean H i density. Combining the results from different frequency channels provides exquisite constraints on the evolution of the HIHMR, especially in the central frequency range of the data cube.