Predictions for the Angular Dependence of Gas Mass Flow Rate and
  Metallicity in the Circumgalactic Medium
  We use cosmological hydrodynamical simulations to examine the physical
properties of the gas in the circumgalactic media (CGM) of star-forming
galaxies as a function of angular orientation. We utilise TNG50 of the
IllustrisTNG project, as well as the EAGLE simulation to show that observable
properties of CGM gas correlate with azimuthal angle, defined as the
galiocentric angle with respect to the central galaxy. Both simulations are in
remarkable agreement in predicting a strong modulation of flow rate direction
with azimuthal angle: inflow is more substantial along the galaxy major axis,
while outflow is strongest along the minor axis. The absolute rates are
noticeably larger for higher (log(M_* / M_sun) ~ 10.5) stellar mass galaxies,
up to an order of magnitude compared to M^dot < 1 M_sun/yr/sr for log(M_* /
M_sun) ~ 9.5 objects. Notwithstanding the different numerical and physical
models, both TNG50 and EAGLE predict that the average metallicity of the CGM is
higher along the minor versus major axes of galaxies. The angular signal is
robust across a wide range of galaxy stellar mass 8.5 < log(M_* / M_sun) < 10.5
at z<1. This azimuthal dependence is particularly clear at larger impact
parameters b > 100 kpc. Our results present a global picture whereby, despite
the numerous mixing processes, there is a clear angular dependence of the CGM
metallicity. We make forecasts for future large survey programs that will be
able to compare against these expectations. Indeed, characterising the
kinematics, spatial distribution and metal content of CGM gas is key to a full
understanding of the exchange of mass, metals, and energy between galaxies and
their surrounding environments.
