Bar formation in submaximal discs: a challenge for \Lambda CDM

Bar formation in cosmological simulations of galaxy formation remains challenging. It was previously shown that the fraction of barred galaxies at low stellar masses ($M_*<10^{10.5} M_\odot$) in TNG50 is too low compared to observations. Here, we highlight another tension, also observed at higher stellar masses, namely that barred galaxies in TNG50 appear to be maximal discs, in the sense that the majority of the gravitational acceleration is accounted for by baryons at the peak radius of the baryonic rotation curve, while observations account for a substantial fraction of barred submaximal discs. In this letter, we compare the barred fraction of submaximal discs in the local Universe from the SPARC catalogue with that in the TNG50 simulation. We show that, although SPARC tends to select against barred galaxies, the fraction of barred submaximal discs in this dataset is significantly larger than in TNG50. This result adds to the list of challenges related to predicting the right statistics and properties of barred galaxies in $\Lambda$CDM simulations of galaxy formation.