Galaxy Zoo: CANDELS Barred Disks and Bar Fractions

TL;DR

This study reports the discovery of strong barred structures in massive disk galaxies at z ~ 1.5, showing that the bar fraction remains relatively constant from z=0.5 to 2, challenging previous expectations about bar evolution.

Contribution

It provides the first evidence of significant barred disks at high redshift (z ~ 1.5) and shows that the bar fraction does not significantly decline over 0.5<z<2, contrary to prior models.

Findings

Bar fraction at 0.5<z<2 is approximately 10.7%.

Strong barred structures are present in galaxies at z ~ 1.5.

Bar incidence does not significantly evolve over the studied redshift range.

Abstract

The formation of bars in disk galaxies is a tracer of the dynamical maturity of the population. Previous studies have found that the incidence of bars in disks decreases from the local Universe to z ~ 1, and by z > 1 simulations predict that bar features in dynamically mature disks should be extremely rare. Here we report the discovery of strong barred structures in massive disk galaxies at z ~ 1.5 in deep rest-frame optical images from CANDELS. From within a sample of 876 disk galaxies identified by visual classification in Galaxy Zoo, we identify 123 barred galaxies. Selecting a sub-sample within the same region of the evolving galaxy luminosity function (brighter than L*), we find that the bar fraction across the redshift range 0.5< z < 2 (f_bar = 10.7 +6.3 -3.5% after correcting for incompleteness) does not significantly evolve. We discuss the implications of this discovery in the context of existing simulations and our current understanding of the way disk galaxies have evolved over the last 11 billion years.