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.
We perform a comprehensive estimate of the frequency of galaxy mergers and their impact on star formation over z ∼ 0.24-0.80 (lookback time T b ∼ 3-7 Gyr) using ∼3600 (M 1 × 10 9 M ) galaxies with GEMS Hubble Space Telescope, COMBO-17, and Spitzer data. Our results are as follows. (1) Among ∼790 high-mass (M 2.5 × 10 10 M ) galaxies, the visually based merger fraction over z ∼ 0.24-0.80, ranges from 9% ± 5% to 8% ± 2%. Lower limits on the major merger and minor merger fraction over this interval range from 1.1% to 3.5%, and 3.6% to 7.5%, respectively. This is the first, albeit approximate, empirical estimate of the frequency of minor mergers over the last 7 Gyr. Assuming a visibility timescale of ∼0.5 Gyr, it follows that over T b ∼ 3-7 Gyr, ∼68% of high-mass systems have undergone a merger of mass ratio >1/10, with ∼16%, 45%, and 7% of these corresponding respectively to major, minor, and ambiguous "major or minor" mergers. The average merger rate is ∼ a few ×10 −4 galaxies Gyr −1 Mpc −3 . Among ∼2840 blue-cloud galaxies of mass M 1.0 × 10 9 M , similar results hold. (2) We compare the empirical merger fraction and merger rate for high-mass galaxies to three Λ cold dark matter-based models: halo occupation distribution models, semi-analytic models, and hydrodynamic SPH simulations. We find qualitative agreement between observations and models such that the (major+minor) merger fraction or rate from different models bracket the observations, and show a factor of 5 dispersion. Near-future improvements can now start to rule out certain merger scenarios. (3) Among ∼3698 M 1.0 × 10 9 M galaxies, we find that the mean star formation rate (SFR) of visibly merging systems is only modestly enhanced compared to non-interacting galaxies over z ∼ 0.24-0.80. Visibly merging systems only account for a small fraction (<30%) of the cosmic SFR density over T b ∼ 3-7 Gyr. This complements the results of Wolf et al. over a shorter time interval of T b ∼ 6.2-6.8 Gyr, and suggests that the behavior of the cosmic SFR density over the last 7 Gyr is predominantly shaped by non-interacting galaxies.
We investigate the properties of optically passive spirals and dusty red galaxies in the A901/2 cluster complex at redshift ∼0.17 using rest-frame near-ultraviolet-optical spectral energy distributions, 24-μm infrared data and Hubble Space Telescope morphologies from the STAGES data set. The cluster sample is based on COMBO-17 redshifts with an rms precision of σ cz ≈ 2000 km s −1 . We find that 'dusty red galaxies' and 'optically passive spirals' in A901/2 are largely the same phenomenon, and that they form stars at a substantial rate, which is only four times lower than that in blue spirals at fixed mass. This star formation is more obscured than in blue galaxies and its optical signatures are weak. They appear predominantly in the stellar mass range of log M * /M = [10, 11] where they constitute over half of the star-forming galaxies in the cluster; they are thus a vital ingredient for understanding the overall picture of star formation quenching in clusters. We find that the mean specific star formation rate (SFR) of star-forming galaxies in the cluster is clearly lower than in the field, in contrast to the specific SFR properties of blue galaxies alone, which appear similar in cluster and field. Such a rich red spiral population is best explained if quenching is a slow process and morphological transformation is delayed even more. At log M * /M < 10, such galaxies are rare, suggesting that their quenching is fast and accompanied by morphological change. We note that edge-on
One third of present-day spirals host optically visible strong bars that drive their dynamical evolution. However, the fundamental question of how bars evolve over cosmological times has yet to be resolved, and even the frequency of bars at intermediate redshifts remains controversial. We investigate the frequency of bars out to z ∼ 1 drawing on a sample of 1590 galaxies from the Galaxy Evolution from Morphology and SEDs survey, which provides morphologies from Hubble Space Telescope Advanced Camera for Surveys (ACS) two-band images and accurate redshifts from the COMBO-17 survey. We identify spiral galaxies using three independent techniques based on the Sersic index, concentration parameter, and rest-frame color. We characterize bar and disk features by fitting ellipses to F606W and F850LP images, using the two bands to minimize shifts in the rest-frame bandpass. We exclude highly inclined (i > 60 • ) galaxies to ensure reliable morphological classifications and apply different completeness cuts of M V ≤ −19.3 and −20.6. More than 40% of the bars that we detect have semi major axes a < 0. ′′ 5 and would be easily missed in earlier surveys without the small point spread function of ACS. The bars that we can reliably detect are fairly strong (with ellipticities e ≥ 0.4) and have a in the range ∼1.2-13 kpc. We find that the optical fraction of such strong bars remains at ∼30% ± 6% from the present-day out to look-back times of 2-6 Gyr (z ∼ 0.2-0.7) and 6-8 Gyr (z ∼ 0.7-1.0); it certainly shows no sign of a drastic decline at z > 0.7. Our findings of a large and similar bar fraction at these three epochs favor scenarios in which cold gravitationally unstable disks are already in place by z ∼ 1 and where on average bars have a long lifetime (well in excess of 2 Gyr). The distributions of structural bar properties in the two slices are, however, not statistically identical and therefore allow for the possibility that the bar strengths and sizes may evolve over time.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2025 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.