Barred galaxies in the EAGLE cosmological hydrodynamical simulation

We examine the properties of barred disc galaxies in a Lambda CDM cosmological hydrodynamical simulation from the EAGLE project. Our study follows the formation of 269 discs identified at z = 0 in the stellar mass range 10.6 < logM(*)/ M circle dot < 11. These discs show a wide range of bar strengths, from unbarred discs (approximate to 60 per cent) to weak bars (approximate to 20 per cent) and to strongly barred systems (approximate to 20 per cent). Bars in these systems develop after redshift approximate to 1.3, on timescales that depend sensitively on the strength of the pattern. Strong bars develop relatively quickly (in a few Gyr, or roughly similar to 10 disc rotation periods) in systems that are disc dominated, gas poor, and have declining rotation curves. Weak bars develop more slowly in systems where the disc is less gravitationally important, and are still growing at z = 0. Unbarred galaxies are comparatively gas- rich discs whose rotation speeds do not exceed the maximum circular velocity of the haloes they inhabit. Bar lengths compare favourably with observations, ranging from 0.2 to 0.8 times the radius containing 90 per cent of the stars. Bars slow down remarkably quickly as they grow, causing the inner regions of the surrounding dark halo to expand. At z = 0 strong bars in simulated galaxies have corotation radii roughly 10 times the bar length. Such slow bars are inconsistent with the few cases where pattern speeds have been measured or inferred observationally, a discrepancy that, if confirmed, might prove a challenge for disc galaxy formation in Lambda CDM.