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 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 ($>60^{\circ}$) 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) $f_{\rm opt-r}$ rises for galaxies with bluer colors (by ~30%) and lower masses (by ~15%-20%). (4) While hierarchical $Λ$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= 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)
Here we present statistical and geochemical data on 12 minor and trace elements from pyrite- and marcasite-bearing samples from drillhole cores in the Sarnak (also known as Surnak) gold deposit. The data were obtained by SEM-EDX and single-spot LA-ICP-MS analyses in marcasite and different pyrite zones – core, mantle, and rim.
We present a study of large-scale bars in the local Universe, based on a large sample of ~3692 galaxies, with -18.5 60 degrees) systems, we find the following results. (1) The optical r-band fraction (f_opt-r) of barred galaxies is ~48%-52%. (2) When galaxies are separated according to normalized half light radius (r_e/R_24), 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 and higher central surface brightness. A weaker rise is seen toward lower masses. (4) We find that ~20% of our sample of disk galaxies appear to be ``quasi-bulgeless''. (5) If we restrict our sample to bright galaxies and only consider bars that are strong (ellipticity >=0.4) and large enough (semi-major axis >=1.5 kpc) to be reliably characterized via ellipse-fitting out to z~0.8, we get an optical r-band fraction for strong bars f_opt-s of ~34%. This value is higher only by a modest factor of 1.4, compared to the value of ~24%+-4% reported at z~0.7-1.0. If one assumes that the increasing obscuration by dust and star formation over z~0 to 1.0 causes a further artificial loss of bars, the data even allow for a constant or rising fraction of strong bars with redshift.
The Coma cluster was the target of a 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 2007, the partially completed survey still covers ~50% of the core high-density region in Coma. Observations were performed for 25 fields that extend over a wide range of cluster-centric radii (~1.75 Mpc) 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 half-light radius. We have performed photometry for ~73,000 unique objects; one-half of our detections are brighter than the 10-sigma point-source 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 objects (primarily GCs but also UCDs) and a wide variety of extended galaxies from a cD galaxy to dwarf LSB galaxies. The red sequence of Coma member galaxies has a constant slope and dispersion across 9 magnitudes (-21
In dense clusters, higher densities at early epochs as well as physical processes, such as ram pressure stripping and tidal interactions become important, and can have direct consequences for the evolution of bars and their host disks. To study bars and disks as a function of environment, we are using the STAGES ACS HST survey of the Abell 901/902 supercluster (z~0.165), along with earlier field studies based the SDSS and the Ohio State University Bright Spiral Galaxy Survey (OSUBSGS). We explore the limitations of traditional methods for characterizing the bar fraction, and in particular highlight uncertainties in disk galaxy selection in cluster environments. We present an alternative approach for exploring the proportion of bars, and investigate the properties of bars as a function of host galaxy color, Sersic index, stellar mass, star formation rate (SFR), specific SFR, and morphology.
Abstract 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 Sérsic 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°) systems our results are: (1) the optical ( r -band) fraction of barred galaxies among local disk galaxies is 43% (Figure 1, left panel), 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 (Figure 1, middle panel); (3) preliminary analyzes suggest that the optical bar fraction increases steeply with the galaxy effective radius ( r eff , Figure 1, right panel); (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.
We present a study of bar and host disk evolution in a dense cluster environment, based on a sample of ~800 bright (MV <= -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, XMM-Newton, and COMBO-17. We identify and characterize bars through ellipse-fitting, and other morphological features through visual classification. (1) 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 S'ersic cut (n <= 2.5), and a blue-cloud cut. In cluster environments, the latter two methods miss 31% and 51%, respectively, of visually-identified disks. (2) For moderately inclined disks, the three methods of disk selection yield a similar global optical bar fraction (f_bar-opt) of 34% +10%/-3%, 31% +10%/-3%, and 30% +10%/-3%, respectively. (3) f_bar-opt 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. For a given morphological class, f_bar-opt rises at higher luminosities. (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 (5) Between the core and the virial radius of the cluster at intermediate environmental densities, the optical bar fraction does not appear to depend strongly on the local environment density and varies at most by a factor of ~1.3. We discuss the implications of our results for the evolution of bars and disks in dense environments.
(ABRIDGED) We use high resolution (~0.1") F814W ACS images from the HST ACS Treasury survey of the Coma cluster at z~0.02 to study bars in massive disk galaxies (S0s), and in dwarf galaxies in the Coma core. Our study helps constrain the evolution of bars and disks in dense environments and provides a comparison point for studies in lower density environments and at higher redshifts. (1) We characterize the fraction and properties of bars in a sample of 32 bright (M_V <= -18, M_* > 10^9.5 M_sun) S0 galaxies, which dominate the population of massive disk galaxies in the Coma core. Measuring the S0 bar fraction must be handled carefully, as the results depend on the method used: the bar fraction for bright S0s in the Coma core is 50%+/-11%, 65%+/-11%, and 60%+/-11% for three methods of bar detection: strict ellipse fit criteria, relaxed ellipse fit criteria, and visual classification. (2) We compare the S0 bar fraction across different environments (Coma core, A901/902, Virgo). We find that the bar fraction among bright S0 galaxies does not show a statistically significant variation across environments spanning two orders of magnitude in galaxy number density (n~300-10,000 gal/Mpc^3). We speculate that the S0 bar fraction is not significantly enhanced in rich clusters because S0s in rich clusters are less prone to bar instabilities as they are dynamically hot and gas poor due to ram pressure stripping and accelerated star formation. In addition, high-speed encounters in rich clusters may be less effective than slow, strong encounters in inducing bars. (3) We analyze a sample of 333 faint (M_V > -18) dwarf galaxies in the Coma core. Using unsharp-masking, we find only 13 galaxies with bar and/or spiral structure. The paucity of disk structures in Coma dwarfs suggests that either disks are not common in these galaxies, or that any disks present are too hot to develop instabilities.
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