Mock HI-galaxy catalogs and HI mass functions for future large-scale surveys

Abstract

One of the interesting modern astrophysics topics is the discrepancy in HI-galaxy number density between the standard model ΛCDM prediction and observations, e.g., ALFALFA and HIPASS. Since then, the simulation over-predicted the abundance and HI mass (MHI) of small satellite and low-mass galaxies. Both problems still require sensitive instruments for wider and deeper HI surveys to increase the number of low-mass HI-galaxy samples. Current HI-galaxy surveys can only reach down to ∼ 107 Solar mass (M⊙). The sensitivity of upcoming radio surveys such as FAST or ASKAP are expected to reach lower MHI and higher redshift(z) HI-galaxy data. Alternatively, the HI source catalogs from cosmological simulations are used to determine the expected HIMF with the upcoming HI survey specification. This work aims to compare the HIMF in various HI conversion recipes. Various HIMF were determined by using the Multidark(Planck) catalog with the box (MB) and the light-cone (ML) types, and were parameterized by the Schechter function. In comparison to the Schechter function, we discovered that the HIMF from cold gas mass (Mcold) conversion method begins to diverge on MHI ≲ 108.5 M⊙. The HIMF from halo mass (Mhalo) recipe, which was constrained by the optical counterpart galaxy clustering, provided a satisfactory relevant shape of HIMF. The best-fit parameter α of MB and ML are equal to 0.00 ± 0.010 and −0.02 ± 0.0026, respectively. The flatter α values from simulations could indicate that the number density of low-MHI is underestimated.