The HI content of dark matter haloes at z ≈ 0 from ALFALFA

We combine information from the clustering of Hi galaxies in the 100 per cent data release of the Arecibo Legacy Fast ALFA survey, and from the H 1 content of optically selected galaxy groups found in the Sloan Digital Sky Survey to constrain the relation between halo mass AA and its average total H1 mass content. MH 1. We model the abundance and clustering of neutral hydrogen through a halo-model-based approach, parametrizing the MH i(Mh) relation as a power law with an exponential mass cut off, To break the degeneracy between the amplitude and low-mass cut-off of the MHI(Mh) relation, we also include a recent measurement of the cosmic H 1 abundance from the 0(.100 sample, We find that all data sets are consistent with a power-law index a = 0.48 0.08 and a cut-off halo mass loglo Mminl(h 1M(D) = 11.18 We compare these results with predictions from slate-of-the-art magnetohydrodynamical simulations, and find both to be in good qualitative agreement, although the data favours a significantly larger cut-off mass that is consistent with the higher cosmic H 1 abundance found in simulations. Both data and simulations seem to predict a similar value for the Ifibias = 0.87810) and shot-noise power (PsN = 4 21:4 [h-I Mpc13) at redshift z = 0.