The redshift evolution of the baryonic Tully-Fisher relation in Simba
  The baryonic Tully-Fisher relation (BTFR) is an important tool for
constraining galaxy evolution models. As 21-cm HI emission studies have been
largely restricted to low redshifts, the redshift evolution of the BTFR is less
studied. The upcoming LADUMA survey (Looking At the Distant Universe with the
MeerKAT Array) will address this. As preparation for LADUMA, we use the Simba
hydrodynamical galaxy formation simulation from the Simba-hires (25 h$^{-1}$
Mpc)$^{3}$ run to generate rotational velocity measures from galaxy rotation
curves ($V_{\rm flat}$) and HI spectral line profile widths ($W_{\rm 50}$ and
$W_{\rm 20}$) at three different redshifts ($z$ = 0, 0.5, and 1). Using these
measures, together with the dark matter velocity dispersion and halo mass, we
consider the redshift evolution of the BTFR of Simba galaxies. We find that
LADUMA will be successful in detecting weak redshift evolution of the BTFR,
provided that auxiliary data is used to distinguish galaxies with disky
morphologies. $W_{\rm 20}$ spectral line widths give lower scatter and more
pronounced redshift evolution compared to $W_{\rm 50}$. We also compare these
rotational velocity measures to the dark matter velocity dispersion across
redshift and galaxy morphology. We find weak redshift evolution between
rotational velocity and the dark matter halo mass, and provide fits for
estimating a galaxy's dark matter halo mass from HI spectral line widths. This
study with Simba showcases the importance of upcoming, deep SKA pathfinder
surveys such as LADUMA, and provides predictions to compare with redshift
evolution of the BTFR and galaxy dark matter content from HI rotational
velocity measures.
