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تسجيل مستخدم جديدConstraints on Bars in the Local Universe from 5000 SDSS Galaxies
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We present the first study of bars in the local Universe, based on the Sloan Digitized Sky Survey (SDSS). The large sample of ~5000 local galaxies provides the largest study to date of local bars and minimizes the effect of cosmic variance. The sample galaxies have M_g<=-18.5 mag and cover the redshift range 0.01<=z<0.04. We use a color cut in the color-magnitude diagram and the Sersic index n to identify disk galaxies. We characterize bars and disks using r-band images and the method of iterative ellipse fits and quantitative criteria developed in Jogee at al. (2004, ApJL, 615, L105). After excluding highly inclined (i>60 degrees) systems our results are: (1) the optical (r-band) fraction of barred galaxies among local disk galaxies is 43%, which confirms the ubiquity of local bars, in agreement with other optical studies based on smaller samples (e.g.Eskridge et al. 2000, AJ, 119, 536, Marinova & Jogee 2006, astro-ph/0608039); (2) the optical bar fraction rises for bluer galaxies, suggesting a relation between bars and star formation; (3) preliminary analyzes suggest that the optical bar fraction increases steeply with the galaxy effective radius; (4) the optical bar fraction at z~0 is ~35% for bright disks (M_g<=-19.3 mag) and strong (bar ellipticity >0.4), large-scale (bar semi-major axis >1.5 kpc) bars, which is comparable to the value of 30+/-6% reported earlier (Jogee et al. 2004) for similar disks and bars at z~0.2-1.0.
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