The low mass end of the neutral gas mass and velocity width functions of
  galaxies in $\Lambda$CDM
  We use the high-resolution Aquarius cosmological dark matter simulations
coupled to the semi-analytic model by Starkenburg et al. (2013) to study the HI
content and velocity width properties of field galaxies at the low mass end in
the context of $\Lambda$CDM. We compare our predictions to the observed ALFALFA
survey HI mass and velocity width functions, and find very good agreement
without fine-tuning, when considering central galaxies. Furthermore, the
properties of the dark matter halos hosting galaxies, characterised by their
peak velocity and circular velocity at 2 radial disk scalelengths overlap
perfectly with the inferred values from observations. This suggests that our
galaxies are placed in the right dark matter halos, and consequently at face
value, we do not find any discrepancy with the predictions from the
$\Lambda$CDM model. Our analysis indicates that previous tensions, apparent
when using abundance matching models, arise because this technique cannot be
straightforwardly applied for objects with masses $M_{vir} < 10^{10}
M_{\odot}$.
