Barred Galaxies in the Illustris-1 and TNG100 Simulations: A Comparison Study

Abstract

Abstract We carry out a comparison study on the bar structure in the Illustris-1 and TNG100 simulations. At z = 0, 8.9% of 1232 disk galaxies with stellar masses in Illustris-1 are barred, while the numbers are 55% of 1269 in TNG100. The bar fraction as a function of stellar mass in TNG100 agrees well with the survey . The median redshifts of bar formation are ∼0.4–0.5 and ∼0.25 in TNG100 and Illustris-1, respectively. Bar fraction generally increases with stellar mass and decreases with gas fraction in both simulations. For galaxies with bars at z = 0, their bar formation time is generally anti-correlated with their gas fraction at high redshift. When the bars were formed, the disk gas fractions were mostly lower than 0.4. The much higher bar fraction in TNG100 probably benefits from the much lower gas fractions in massive disk galaxies since z ∼ 3, which may result from the combination of more effective stellar and AGN feedback. The latter may be the primary factor at z < 2. Meanwhile, in both simulations, barred galaxies have higher star formation rates before bar formation and have stronger AGN feedback, at all times, than unbarred galaxies. The properties of dark matter halos hosting massive disk galaxies are similar between the two simulations and should have a minor effect on the frequencies of different bars. For individual galaxies under similar halo environments across the two simulations, different baryonic physics can lead to striking discrepancies in morphology. The morphologies of individual galaxies are subject to the combined effects of environment and internal baryonic physics and are often not predictable.