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%.