Barred galaxies in the EAGLE cosmological hydrodynamical simulation

TL;DR

This study investigates the formation and properties of barred disc galaxies in the EAGLE cosmological simulation, revealing how bar strength, growth, and dynamics relate to galaxy characteristics and potential challenges for LCDM models.

Contribution

It provides a detailed analysis of bar formation, evolution, and dynamics in simulated galaxies, highlighting discrepancies with observational pattern speeds.

Findings

Strong bars develop quickly in disc-dominated, gas-poor galaxies.

Bars slow down rapidly as they grow, affecting dark halo structure.

Unbarred, gas-rich discs lack significant bars and have different rotation properties.

Abstract

We examine the properties of barred disc galaxies in a LCDM 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 < log Mstr /M < 11. These discs show a wide range of bar strengths, from unbarred discs to weak bars to strongly barred systems (= 20%). Bars in these systems develop after redshift = 1.3, on timescales that depend sen- sitively on the strength of the pattern. Strong bars develop relatively quickly (in a few Gyr, = 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 gravitation- ally 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 halos they inhabit. Bar lengths compare favourably with observations, ranging from 0.2 to 0.8 times the radius containing 90% 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 have corota- tion radii roughly ten 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 LCDM.