The evolution of barred galaxies in the EAGLE simulations

Abstract

We study the morphologies of 3,964 galaxies and their progenitors with 𝑀 ★ > 10 10 𝑀 in the reference EAGLE hydrodynamical simulation from redshifts 𝑧 = 1 to 𝑧 = 0, concentrating on the redshift evolution of the bar fraction. We apply two convolutional neural networks (CNNs) to classify 35,082 synthetic g-band images across 10 snapshots in redshift. We identify galaxies as either barred or unbarred, while also classifying each sample into one of four morphological types: elliptical (E), lenticular (S0), spiral (Sp), and irregular/miscellaneous (IrrM). We find that the bar fraction is roughly constant between 𝑧 = 0.0 to 𝑧 = 0.5 (32% to 33%), before exhibiting a general decline to 26% out to 𝑧 = 1. The bar fraction is highest in spiral galaxies, from 49% at 𝑧 = 0 to 39% at 𝑧 = 1. The bar fraction in S0s is lower, ranging from 22% to 18%, with similar values for the miscellaneous category. Under 5% of ellipticals were classified as barred. We find that the bar fraction is highest in low mass galaxies (𝑀 ★ ≤ 10 10.5 𝑀 ). Through tracking the evolution of galaxies across each snapshot, we find that some barred galaxies undergo episodes of bar creation, destruction and regeneration, with a mean bar lifetime of 2.24 Gyr. We further find that incidences of bar destruction are more commonly linked to major merging, while minor merging and accretion is linked to both bar creation and destruction.