Testing Galaxy Formation Simulations with Damped Lyman-${\alpha}$
  Abundance and Metallicity Evolution
  We examine the properties of damped Lyman-$\alpha$ absorbers (DLAs) emerging
from a single set of cosmological initial conditions in two state-of-the-art
cosmological hydrodynamic simulations: {\sc Simba} and {\sc Technicolor Dawn}.
The former includes star formation and black hole feedback treatments that
yield a good match with low-redshift galaxy properties, while the latter uses
multi-frequency radiative transfer to model an inhomogeneous ultraviolet
background (UVB) self-consistently and is calibrated to match the Thomson
scattering optical depth, UVB amplitude, and Ly-$\alpha$ forest mean
transmission at $z>5$. Both simulations are in reasonable agreement with the
measured stellar mass and star formation rate functions at $z\geq 3$, and both
reproduce the observed neutral hydrogen cosmological mass density, $\Omega_{\rm
HI}(z)$. However, the DLA abundance and metallicity distribution are sensitive
to the galactic outflows' feedback and the UVB amplitude. Adopting a strong UVB
and/or slow outflows under-produces the observed DLA abundance, but yields
broad agreement with the observed DLA metallicity distribution. By contrast,
faster outflows eject metals to larger distances, yielding more metal-rich DLAs
whose observational selection may be more sensitive to dust bias. The DLA
metallicity distribution in models adopting an ${\rm H}_2$-regulated star
formation recipe includes a tail extending to $[M/H] \ll -3$, lower than any
DLA observed to date, owing to curtailed star formation in low-metallicity
galaxies. Our results show that DLA observations play an imporant role in
constraining key physical ingredients in galaxy formation models, complementing
traditional ensemble statistics such as the stellar mass and star formation
rate functions.
