High-redshift Merger-induced Bar-like Galaxies in IllustrisTNG

Abstract: Recent discoveries made with JWST observations include a significant number of barred galaxies at high redshift. Their origin remains unclear and their presence seems difficult to reproduce in cosmological simulations of galaxy formation and evolution. In this Letter I present four examples of high-redshift bars selected from a sample of bar-like galaxies studied previously using IllustrisTNG simulations. All the galaxies formed their bars at redshifts z > 3 via mergers with smaller satellites, although one had its bar formed even earlier, at z > 5. The bars were born long, with lengths on the order of 3 kpc, and grew in time. Three of the four galaxies were later accreted by clusters and underwent multiple interactions with their respective brightest cluster galaxies. Their bar strength was to some extent affected by these interactions but all the galaxies preserved their bar-like shape until the present time. By the end of the evolution, all the galaxies lost their gas and stopped forming stars, they retained essentially no disk component and were no longer rotationally supported. The examples demonstrate that high-z bars do not evolve into present-day barred disk galaxies similar to the Milky Way but rather into S0s or ellipticals typically found in galaxy clusters.