Bars in Disk-Dominated and Bulge-Dominated Galaxies at z~0: New Insights from ~3600 SDSS Galaxies
2003
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Abstract: (arXiv)
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 S\'ersic 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 () 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/R_24, 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/R_24 and visually appear to host prominent bulges, to ~70% for galaxies that have large r_e/R_24 and appear disk-dominated. (3)~f_opt-r rises for galaxies with bluer colors, lower masses, or fainter luminosities. (4) While hierarchical CDM 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) After applying the same cutoffs in magnitude (M_V<-19.3 mag), bar size (a_bar >= 1.5 kpc), and bar ellipticity (e_bar >=~0.4) that studies out to z~1 apply to ensure a complete sample, adequate spatial resolution, and reliable bar identification, we obtain an optical r-band bar fraction of 34%. This is comparable to the value reported at z~0.2-1.0, implying that the optical bar fraction does not decline dramatically by an order of magnitude in bright galaxies out to z~1. (abridged)Note:
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- accepted for publication in ApJ, 50 pages, 20 figures
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