Angular momentum-related probe of cold gas deficiencies
  Recent studies of neutral atomic hydrogen (HI) in nearby galaxies found that
all field disk galaxies are HI saturated, in that they carry roughly as much HI
as permitted before this gas becomes gravitationally unstable. By taking this
HI saturation for granted, the atomic gas fraction $f_{\rm atm}$ of galactic
disks can be predicted as a function of the stability parameter
$q=j\sigma/(GM)$, where $M$ and $j$ are the baryonic mass and specific angular
momentum of the disk and $\sigma$ is the HI velocity dispersion Obreschkow et
al. 2016. The log-ratio $\Delta f_q$ between this predictor and the observed
atomic fraction can be seen as a physically motivated `HI deficiency'. While
field disk galaxies have $\Delta f_q \approx0$, objects subject to
environmental removal of HI are expected to have $\Delta f_q>0$. Within this
framework, we revisit the HI deficiencies of satellite galaxies in the Virgo
cluster and in clusters of the EAGLE simulation. We find that observed and
simulated cluster galaxies are HI deficient and that $\Delta f_q$ slightly
increases when getting closer to the cluster centres. The $\Delta f_q$ values
are similar to traditional HI deficiency estimators, but $\Delta f_q$ is more
directly comparable between observations and simulations than morphology-based
deficiency estimators. By tracking the simulated HI deficient cluster galaxies
back in time, we confirm that $\Delta f_q\approx0$ until the galaxies first
enter a halo with $M_{\rm halo}>10^{13} {\rm M_{\odot}}$, at which moment they
quickly lose HI by environmental effects. Finally, we use the simulation to
investigate the links between $\Delta f_q$ and quenching of star formation.
