Characterizing bars at z~0 in the optical and NIR : implications for the evolution of barred disks with redshift
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Critical insights on galaxy evolution stem from the study of bars. With the advent of high redshift HST surveys that trace bars in the rest-frame optical band out to z [more or less] 1, it becomes increasingly important to provide a reference baseline for bars at z [more or less] 0 in the optical band. We present results on bars at z [more or less] 0 in the optical and near-infrared bands, based on 180 spirals in the OSUBSGS survey. (1) The deprojected bar fraction at z [more or less] 0 is [function]NIR1 [more or less] 60% [plus or minus] 6% in the near-infrared H band, and [function]optical1[more or less]44% [plus or minus] 6% in the optical B-band images. The latter likely miss bars obscured by dust and star formation. (2) The results before and after deprojection are similar, which is encouraging for high redshift studies that forego deprojection. (3) Studies of bars at z [more or less] 0.2 -1.0 (lookback times of 3-8 Gyr) have reported an optical bar fraction of [function]optical2 [more or less] 30% [plus or minus] 6%, after applying cutoffs in absolute magnitude (MV <-19.3), bar size (abar [greater than or equal to] 1.5 kpc), and bar ellipticity (ebar [greater than or equal to] 0.4) in order to ensure a complete sample, adequate spatial resolution, and reliable bar identification out to z [more or less] 1. Applying these exact cutoffs in magnitude, bar size, and bar ellipticity to the OSUBSGS data yields a comparable optical B- and bar fraction at z [more or less] 0 of [function]optical3 [more or less] 34% [plus or minus] 6%. This rules out scenarios where the optical bar fraction in bright disks declines strongly with redshift. (3)We investigate bar strengths at z [more or less] 0 using the maximum bar ellipticity (ebar) as a guide. Most ( [more or less] 70%) bars have moderate to high ellipticity (0.50 [less than or equal to] ebar [less than or equal to] 0.75), and only a small fraction (7%-10%) have 0.25 [less than or equal to] ebar [less than or equal to] 0.40. There is no bimodality in the distribution of ebar. The H-band bar fraction and ebar show no substantial variation across RC3 Hubble types Sa to Scd. (4) RC3 bar types should be used with caution. Many galaxies with RC3 types `AB' turn out to be unbarred and RC3 bar classes `B' and `AB' have a significant overlap in ebar. (5) Most (68% in B and 76% in H) bars have sizes below 5 kpc. Bar and disk sizes correlate, and the ratio (abar/R25) lies primarily in the range 0.1 to 0.5. This suggests that the growth of bars and disks is intimately tied.