Simulated Bars May Be Shorter But Are Not Slower Than Observed: TNG50
  vs. MaNGA
  Galactic bars are prominent dynamical structures within disk galaxies whose
size, formation time, strength, and pattern speed influence the dynamical
evolution of their hosts galaxies. Yet, their formation and evolution in a
cosmological context is not well understood, as cosmological simulation studies
have been limited by the classic trade off between simulation volume and
resolution. Here we analyze barred disk galaxies in the cosmological
magneto-hydrodynamical simulation TNG50 and quantitatively compare the
distributions of bar size and pattern speed to those from MaNGA observations at
$z=0$. TNG50 galaxies are selected to match the stellar mass and size
distributions of observed galaxies, to account for observational selection
effects. We find that the high-resolution of TNG50 yields bars with a wide
range of pattern speeds (including those with $\geq
40~\mathrm{km}\,\mathrm{s}^{-1}$\,$\mathrm{kpc}^{-1}$) and a mean value of
$\sim36~\mathrm{km}\,\mathrm{s}^{-1}\,\mathrm{kpc}$ consistent with
observations within $6\,\mathrm{km}\,\mathrm{s}^{-1}$\,$\mathrm{kpc}^{-1}$, in
contrast with previous lower-resolution cosmological simulations that produced
bars that were too slow. We find, however, that bars in TNG50 are on average
$\sim 35\%$ shorter than observed, although this discrepancy may partly reflect
remaining inconsistencies in the simulation-data comparison. This leads to
higher values of $\mathcal{R} = R_\mathrm{corot}/R_\mathrm{bar}$ in TNG50, but
points to simulated bars being `too short' rather than `too slow'. After
repeating the analysis on the lower-resolution run of the same simulation (with
the same physical model), we qualitatively reproduce the results obtained in
previous studies: this implies that, along with physical model variations,
numerical resolution effects may explain the previously found `slowness' of
simulated bars.
