The Next Generation X-ray Galaxy Survey with eROSITA
  eROSITA, launched on 13 July 2019, will be completing the first all-sky
survey in the soft and medium X-ray band in nearly three decades. This 4-year
survey, finishing in late 2023, will present a rich legacy for the entire
astrophysics community and complement upcoming multi-wavelength surveys (with,
e.g. the Large Synoptic Survey Telescope and the Dark Energy Survey). Besides
the major scientific aim to study active galactic nuclei (AGN) and galaxy
clusters, eROSITA will contribute significantly to X-ray studies of normal
(i.e., not AGN) galaxies. Starting from multi-wavelength catalogues, we measure
star formation rates and stellar masses for 60 212 galaxies constrained to
distances of 50-200 Mpc. We chose this distance range to focus on the
relatively unexplored volume outside the local Universe, where galaxies will be
largely spatially unresolved and probe a range of X-ray luminosities that
overlap with the low luminosity and/or highly obscured AGN population. We use
the most recent X-ray scaling relations as well as the on-orbit eROSITA
instrument performance to predict the X-ray emission from XRBs and diffuse hot
gas and to perform both an analytic prediction and an end-to-end simulation
using the mission simulation software, SIXTE. We consider potential
contributions from hidden AGN and comment on the impact of normal galaxies on
the measurement of the faint end of the AGN luminosity function. We predict
that the eROSITA 4-year survey, will detect $\gtrsim$ 15 000 galaxies (3
$\sigma$ significance) at 50-200 Mpc, which is ~100X more normal galaxies than
detected in any X-ray survey to date.
