Barred Galaxies in the IllustrisTNG Simulation
  Almost two-thirds of disk galaxies in the local universe host bars, which
serve as important drivers of secular evolutionary processes. While
cosmological simulations are powerful tools to study the formation and
evolution of galaxies, they have often struggled to generate reasonable bar
populations. We measure the fraction, size, and strength of bars in 3866 disk
galaxies from the TNG100 run of the advanced cosmological simulation
IllustrisTNG. Consistent with observations, about 55% of disk galaxies with
stellar mass $M_* \approx 10^{10.6}\, M_\odot$ are barred, and the relation
between bar size and total stellar mass is similar to that found in
near-infrared surveys. However, the formation of bars is suppressed in galaxies
with $M_* < 10^{10.6}\, M_\odot$, which may result from the difficulty TNG100
has in resolving short bars with radius <1.4 kpc. In contrast, up to 75% of
massive disk galaxies with $M_* > 10^{10.6}\, M_\odot$ have bars, ~10%-20%
higher than observed. TNG100 overproduces relatively short bars (radius ~1.4-3
kpc) with respect to the mass-bar size relation observed in near-infrared
surveys. Tracing the progenitors of z=0 massive galaxies we find that the bar
fraction increases from 25% to 63% between z=1 and 0. Instead if we select all
disk galaxies during z=0-1 with a constant mass cut of $M_* \geqslant
10^{10.6}\, M_\odot$ we find that the bar fraction is a nearly constant 60%.
