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

We combine information from the clustering of HI galaxies in the 100% data release of the Arecibo Legacy Fast ALFA survey (ALFALFA), and from the HI content of optically-selected galaxy groups found in the Sloan Digital Sky Survey (SDSS) to constrain the relation between halo mass M<SUB>h</SUB> and its average total HI mass content M<SUB>HI</SUB>. We model the abundance and clustering of neutral hydrogen through a halo-model-based approach, parametrizing the M<SUB>HI</SUB>(M<SUB>h</SUB>) relation as a power law with an exponential mass cutoff. To break the degeneracy between the amplitude and low-mass cutoff of the M<SUB>HI</SUB>(M<SUB>h</SUB>) relation, we also include a recent measurement of the cosmic HI abundance from the α.100 sample. We find that all datasets are consistent with a power-law index α = 0.48 ± 0.08 and a cutoff halo mass log _{10}M_min/(h^{-1}M_☉ )=11.18^{+0.28}_{-0.35}. We compare these results with predictions from state-of-the-art magneto-hydrodynamical simulations, and find both to be in good qualitative agreement, although the data favours a significantly larger cutoff mass that is consistent with the higher cosmic HI abundance found in simulations. Both data and simulations seem to predict a similar value for the HI bias (b_HI=0.878^{+0.022}_{-0.023}) and shot-noise power (P_SN=94^{+20}_{-18} [h^{-1}Mpc]^3) at redshift z = 0.