Bars in Disk-dominated and Bulge-dominated Galaxies at z ~ 0: New Insights from ~3600 SDSS Galaxies

Abstract

We present a study of large-scale bars in the local universe, based on a large sample of 3692 galaxies, with 18.5 <= M_g < - 22.0 mag and redshift 0.01 <= z < 0.03, drawn from the Sloan Digitized Sky Survey. Our sample includes many galaxies that are disk-dominated and of late Hubble types. Both color cuts and Sérsic cuts yield a similar sample of ~2000 disk galaxies. We characterize bars and disks by ellipse-fitting r-band images and applying quantitative criteria. After excluding highly inclined (60°) systems, we find the following results. (1) The optical r-band fraction (f_{opt - r}) of barred galaxies, when averaged over the whole sample, is ~48%-52%. (2) When galaxies are separated according to half light radius (r_e), or normalized r_e/R₂₄, which is a measure of the bulge-to-disk (B/D) ratio, a remarkable result is seen: f_{opt - r} rises sharply, from ~40% in galaxies that have small r_e/R₂₄ and visually appear to host prominent bulges, to ~70% for galaxies that have large r_e/R₂₄ and appear disk-dominated. (3) For galaxies with bluer colors, f_{opt - r} rises significantly (by ~30%). A weaker rise (by ~15%-20%) is seen for lower luminosities or lower masses. (4) While hierarchical ΛCDM models of galaxy evolution models fail to produce galaxies without classical bulges, our study finds that ~20% of disk galaxies appear to be ``quasi-bulgeless." (5) We outline how the effect of a decreasing resolution and a rising obscuration of bars by gas and dust over z = 0.2-1.0 can cause a significant artificial loss of bars, and an artificial reduction in the optical bar fraction over z = 0.2-1.0.