Characterizing Bars at Z ∼ 0 in the Optical and Nir: Implications for the Evolution of Barred Disks with Redshift

Critical insights on galaxy evolution stem from the study of bars. With the advent of high redshiftHST surveys that trace bars in the rest-frame optical band out to z ∼ 1, it becomes increasingly important to provide a reference baseline for bars at z ∼ 0 in the optical band. We present results on bars at z ∼ 0 in the optical and near-infrared bands, based on 180 spirals in the OSUBSGS survey. (1) The deprojected bar fraction at z ∼ 0 is fNIR1 ∼ 60% ± 6% in the near-infrared H band, and foptical1∼ 44% ± 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 ∼ 0.2–1.0 (lookback times of 3–8 Gyr) have reported an optical bar fraction of foptical2∼ 30% ± 6%, after applying cutoffs in absolute magnitude (MV <-19.3), bar size (abar ≥ 1.5 kpc), and bar ellipticity (ebar ≥ 0.4) in order to ensure a complete sample, adequate spatial resolution, and reliable bar identification out to z ∼ 1. Applying these exact cutoffs in magnitude, bar size, and bar ellipticity to the OSUBSGS data yields a comparable optical B-band bar fraction at z ∼ 0 of foptical3∼ 34% ± 6%. This rules out scenarios where the optical bar fraction in bright disks declines strongly with redshift. (4) We investigate bar strengths at z ∼ 0 using the maximum bar ellipticity (ebar) as a guide. Most (∼ 70%) bars have moderate to high ellipticity (0.50 ≤ ebar ≤ 0.75), and only a small fraction (7%–10%) have 0.25 ≤ ebar ≤ 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. (5) 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. (6) 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. Subject headings: galaxies: fundamental parameters — galaxies: structure — galaxies: kinematics and dynamics — galaxies: evolution