Angular momentum regulates HI gas content and HI central hole size in
  the discs of spirals
  The neutral atomic hydrogen (HI) content of spiral galaxies has been observed
to vary with environment, with more HI-deficient spirals residing in high
density environments. This can be attributed to environmental effects such as
ram pressure stripping and tidal interactions, which remove HI from the discs
of galaxies. However, some spirals in low-density environments have also been
observed to have relatively low HI mass fractions. The low densities of the
Intergalactic Medium and lack of nearby galaxies in such environments make ram
pressure stripping and tidal interactions unlikely candidates of gas removal.
What then could be making these spirals HI deficient? Obreschkow et al.
introduced a parameter-free model for the neutral atomic gas fraction
($f_{atm}$), in a symmetric equilibrium disc as a function of the global atomic
stability parameter ($q$), which depends on specific angular momentum. In order
to examine if this model accounts for HI-deficient galaxies in low-density
environments, we have used the $M_{HI} ~-$ M$_{R}$ scaling relation to select
six HI-deficient spiral galaxies and observed them with the ATCA. By measuring
their $f_{atm}$ and $q$ values we find that the galaxies owe their observed HI
deficiencies to low specific angular momenta. Additionally, we also find that
the central HI hole sizes of our sample galaxies are related to their $q$
values, following the prediction of Obreschkow et al. This result brings to
light the importance of angular momentum in understanding the physics of the
interstellar medium in the discs of galaxies and consequently their evolution.
