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 < À22:0 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 optÀr ) 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 optÀr 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) For galaxies with bluer colors, f optÀr rises significantly (by $30%). A weaker rise (by $15%Y20%) is seen for lower luminosities or lower masses. (4) While hierarchical ÃCDM 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 ¼ 0:2Y1:0 can cause a significant artificial loss of bars, and an artificial reduction in the optical bar fraction over z ¼ 0:2Y1:0.

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 ∼ 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 f NIR1 ∼ 60% ± 6% in the near-infrared H band, and f optical1 ∼ 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 f optical2 ∼ 30% ± 6%, after applying cutoffs in absolute magnitude (M V <-19.3), bar size (a bar ≥ 1.5 kpc), and bar ellipticity (e bar ≥ 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 f optical3 ∼ 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 (e bar ) as a guide. Most (∼ 70%) bars have moderate to high ellipticity (0.50 ≤ e bar ≤ 0.75), and only a small fraction (7%-10%) have 0.25 ≤ e bar ≤ 0.40. There is no bimodality in the distribution of e bar . The H-band bar fraction and e bar 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 e bar . (6) Most (68% in B and 76% in H) bars have sizes below 5 kpc. Bar and disk sizes correlate, and the ratio (a bar /R 25 ) lies primarily in the range 0.1 to 0.5. This suggests that the growth of bars and disks is intimately tied. 2 We assume in this paper a flat cosmology with Ω M = 1 − Ω Λ = 0.3 and H 0 =70 km s −1 Mpc −1 .

We present the survey design, data reduction, and spectral fitting pipeline for the VIRUS-P Exploration of Nearby Galaxies (VENGA). VENGA is an integral field spectroscopic survey, which maps the disks of 30 nearby spiral galaxies. Targets span a wide range in Hubble type, star formation activity, morphology, and inclination. The VENGA data-cubes have 5.6 ′′ FWHM spatial resolution, ∼ 5Å FWHM spectral resolution, sample the 3600Å-6800Å range, and cover large areas typically sampling galaxies out to ∼ 0.7R 25 . These data-cubes can be used to produce 2D maps of the star formation rate, dust extinction, electron density, stellar population parameters, the kinematics and chemical abundances of both stars and ionized gas, and other physical quantities derived from the fitting of the stellar spectrum and the measurement of nebular emission lines. To exemplify our methods and the quality of the data, we present the VENGA data-cube on the face-on Sc galaxy NGC 628 (a.k.a. M 74). The VENGA observations of NGC 628 are described, as well as the construction of the datacube, our spectral fitting method, and the fitting of the stellar and ionized gas velocity fields. We also propose a new method to measure the inclination of nearly face-on systems based on the matching of the stellar and gas rotation curves using asymmetric drift corrections. VENGA will measure relevant physical parameters across different environments within these galaxies, allowing a series of studies on star formation, structure assembly, stellar populations, chemical evolution, galactic feedback, nuclear activity, and the properties of the interstellar medium in massive disk galaxies.

The Coma cluster, Abell 1656, was the target of an HST-ACS Treasury program designed for deep imaging in the F475W and F814W passbands. Although our survey was interrupted by the ACS instrument failure in early 2007, the partially completed survey still covers ∼50% of the core highdensity region in Coma. Observations were performed for 25 fields that extend over a wide range of cluster-centric radii (∼1.75 Mpc or 1 • ) with a total coverage area of 274 arcmin 2 . The majority of the fields are located near the core region of Coma (19/25 pointings) with six additional fields in the south west region of the cluster. In this paper we present reprocessed images and SExtractor source catalogs for our survey fields, including a detailed description of the methodology used for object detection and photometry, the subtraction of bright galaxies to measure faint underlying objects, and the use of simulations to assess the photometric accuracy and completeness of our catalogs. We also use simulations to perform aperture corrections for the SExtractor Kron magnitudes based only on the measured source flux and its half-light radius. We have performed photometry for ∼73,000 unique objects; approximately one-half of our detections are brighter than the 10σ pointsource detection limit at F814W=25.8 mag (AB). The slight majority of objects (60%) are unresolved or only marginally resolved by ACS. We estimate that Coma members are 5%-10% of all source detections, which consist of a large population of unresolved compact sources (primarily globular clusters but also ultra-compact dwarf galaxies) and a wide variety of extended galaxies from a cD galaxy to dwarf low surface brightness galaxies. The red sequence of Coma member galaxies has a color-magnitude relation with a constant slope and dispersion over 9 magnitudes (-21

We present a study of bar and host disk evolution in a dense cluster environment, based on a sample of ∼ 800 bright (M V ≤ −18) galaxies in the Abell 901/2 supercluster at z ∼ 0.165. We use HST ACS F606W imaging from the STAGES survey, and data from Spitzer, XM M − N ewton, and COMBO-17. We identify and characterize bars through ellipse-fitting, and other morphological features through visual classification. We find the following results: (1) To define the optical fraction of barred disk galaxies, we explore three commonly used methods for selecting disk galaxies. We find 625, 485, and 353 disk galaxies, respectively, via visual classification, a single component Sérsic cut (n ≤ 2.5), and a blue-cloud cut. In cluster environments, the latter two methods suffer from serious limitations, and miss 31% and 51%, respectively, of visually-identified disks, particularly the many red, bulge-dominated disk galaxies in clusters.(2) For moderately inclined disks, the three methods of disk selection, however, yield a similar global optical bar fraction (f bar−opt ) of 34% +10% −3% (115/340), 31% +10% −3% (58/189), and 30% +10% −3% (72/241), respectively. (3) We explore f bar−opt as a function of host galaxy properties and find that it rises in brighter galaxies and those which appear to have no significant bulge component. Within a given absolute magnitude bin, f bar−opt is higher in visually-selected disk galaxies that have no bulge as opposed to those with bulges. Conversely, for a given visual morphological class, f bar−opt rises at higher luminosities. Both results are similar to trends found in the field. (4) For bright early-types, as well as faint late-type systems with no evident bulge, the optical bar fraction in the Abell 901/2 clusters is comparable within a factor of 1.1 to 1.4 to that of field galaxies at lower redshifts (z < 0.04). (5) Between the core and the virial radius of the cluster (R ∼ 0.25 to 1.2 Mpc) at intermediate environmental densities (log(Σ 10 )∼ 1.7 to 2.3), the optical bar fraction does not appear to depend strongly on the local environment density tracers (κ, Σ 10 , and ICM density), and varies at most by a factor of ∼ 1.3. Inside the cluster core, we are limited by number statistics, projection effects, and different trends from different indicators, but overall f bar−opt does not show evidence for a variation larger than a factor of 1.5. We discuss the implications of our results for the evolution of bars and disks in dense environments.