A constant bar fraction out to redshift z ∼ 1 in the advanced camera for surveys field of the Tadpole galaxy

Abstract

Barlike structures were investigated in a sample of 186 disk galaxies larger than 0″.5 that are in the I-band image of the Tadpole galaxy taken with the Hubble Space Telescope Advanced Camera for Surveys. We found 22 clear cases of barred galaxies, 21 galaxies with small bars that appear primarily as isophotal twists in a contour plot, and 11 cases of peculiar bars in clump-cluster galaxies, which are face-on versions of chain galaxies. The latter bars are probably young, as the galaxies contain only weak interclump emission. Four of the clearly barred galaxies at z ∼ 0.8-1.2 have grand-design spirals. The bar fraction was determined as a function of galaxy inclination and compared with the analogous distribution in the local universe. The bar fraction was also determined as a function of galaxy angular size. These distributions suggest that inclination and resolution effects obscure nearly half of the bars in our sample. The bar fraction was also determined as a function of redshift. We found a nearly constant bar fraction of 0.23 ± 0.03 from z ∼ 0 to z = 1.1. When corrected for inclination and size effects, this fraction is comparable to the bar fraction in the local universe, ∼0.4, which we tabulated for all bar and Hubble types in the Third Reference Catalogue of Bright Galaxies. The average major axis of a barred galaxy in our sample is ∼10 kpc after correcting for redshift with a Λ-dominated cold dark matter cosmology. The average exponential scale length is ∼2 kpc. These are half the sizes of local barred galaxies and not likely to be influenced much by cosmological dimming, because the high-z galaxies are intrinsically brighter. We conclude that galaxy bars were present in normal abundance at least ∼8 Gyr ago (z ∼ 1); the bars in clump-cluster galaxies may have formed from gaseous disk instabilities and star formation rather than stellar disk instabilities, and bar dissolution cannot be common during a Hubble time unless the bar formation rate is comparable to the dissolution rate. If galaxy interactions trigger bar formation more than bar destruction, then the higher interaction rate in the past suggests relatively few bars actually dissolved in a Hubble time.