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The MaNGA project has obtained integral field unit (IFU) data for several thousand nearby galaxies, including barred galaxies. With the two-dimensional spectral and kinematic information provided by IFUs, we can measure the pattern speed of a barred galaxy, which determines the bar dynamics. We apply the non-parametric method proposed by Tremaine & Weinberg to estimate the bar pattern speed for 53 barred galaxies, making this the largest sample studied so far in this way. Our sample is selected from the MaNGA first public data release as part of SDSS Data Release 13 according mainly to the axial ratio and position angle difference between the bar and disc, while kinematic data are from the later SDSS Data Release 14. We have used both the photometric position angle from the photometric image and the kinematic position angle from the stellar velocity map to derive the pattern speed. Combining three independent bar length measurements and the circular velocity from Jeans anisotropic modelling (JAM), we also determine the dimensionless ratio |$\cal {R}$| of the corotation radius to the bar length. We find that the galaxy's position angle is the main uncertainty in determining the bar pattern speed. The kinematic position angle leads to fewer ultrafast bars than the photometric position angle, and this could be due to the method of measuring the kinematic position angle. We study the dependence of |$\cal {R}$| values on galaxy properties such as the dark matter fraction from JAM modelling and the stellar age and metallicity from stellar population synthesis. A positive correlation between the bar length and bar strength is found: the longer the bar, the stronger the bar. However, no other significant correlations are found. This may result from errors in deriving the |$\cal {R}$| values or from the complex formation and slowdown processes of galactic bars. [ABSTRACT FROM AUTHOR]

Due to the non-axisymmetric potential of the central bar, in addition to their characteristic arms and bar, barred spiral galaxies form a variety of structures within the thin gas disk, such as nuclear rings, inner spirals, and dust lanes. These structures in the inner kiloparsec are extremely important in order to explain and understand the rate of black hole feeding. The aim of this work is to investigate the influence of stellar bars in spiral galaxies on the thin self-gravitating gas disk. We focus on the accretion of gas onto the central supermassive black hole and its time-dependent evolution. We conducted multi-scale simulations simultaneously resolving the galactic disk and the accretion disk around the central black hole. In all the simulations we varied the initial gas disk mass. As an additional parameter we chose either the gas temperature for isothermal simulations or the cooling timescale for non-isothermal simulations. Accretion was either driven by a gravitationally unstable or clumpy accretion disk or by energy dissipation in strong shocks. Most of the simulations show a strong dependence of the accretion rate at the outer boundary of the central accretion disk (r < 300 pc) on the gas flow at kiloparsec scales. The final black hole masses reach up to ~109 M⊙ after 1.6 Gyr. Our models show the expected influence of the Eddington limit and a decline in growth rate at the corresponding sub-Eddington limit. [ABSTRACT FROM AUTHOR]

The escape dynamics of the stars in a barred galaxy composed of a spherically symmetric central nucleus, a bar, a flat thin disc and a dark matter halo component is investigated by using a realistic three degrees of freedom (3-d.o.f.) dynamical model. Modern colour-coded diagrams are used for distinguishing between bounded and escaping motion. In addition, the smaller alignment index method is deployed for determining the regular, sticky or chaotic nature of bounded orbits. We reveal the basins of escape corresponding to the escape through the two symmetrical escape channels around the Lagrange points L2 and L3 and also we relate them with the corresponding distribution of the escape times of the orbits. Furthermore, we demonstrate how the stable manifolds, around the index-1 saddle points, accurately define the fractal basin boundaries observed in the colour-coded diagrams. The development scenario of the fundamental vertical Lyapunov periodic orbit is thoroughly explored for obtaining a more complete view of the unfolding of the singular behaviour of the dynamics at the cusp values of the parameters. Finally, we examine how the combination of the most important parameters of the bar (such as the semimajor axis and the angular velocity) influences the observed stellar structures (rings and spirals), which are formed by escaping stars guided by the invariant manifolds near the saddle points. [ABSTRACT FROM AUTHOR]

Dark gaps are commonly seen in early-to-intermediate-type barred galaxies having inner and outer rings or related features. In this paper, the morphologies of 54 barred and oval ringed galaxies have been examined with the goal of determining what the dark gaps are telling us about the structure and evolution of barred galaxies. The analysis is based mainly on galaxies selected from the Galaxy Zoo 2 data base and the Catalogue of Southern Ringed Galaxies. The dark gaps between inner and outer rings are of interest because of their likely association with the L4 and L5 Lagrangian points that would be present in the gravitational potential of a bar or oval. Since the points are theoretically expected to lie very close to the corotation resonance (CR) of the bar pattern, the gaps provide the possibility of locating corotation in some galaxies simply by measuring the radius rgp of the gap region and setting rCR=rgp.With the additional assumption of generally flat rotation curves, the locations of other resonances can be predicted and compared with observed morphological features. It is shown that this 'gap method' provides remarkably consistent interpretations of the morphology of early-tointermediate-type barred galaxies. The paper also brings attention to cases where the dark gaps lie inside an inner ring, rather than between inner and outer rings. These may have a different origin compared to the inner/outer ring gaps. [ABSTRACT FROM AUTHOR]

For several decades, it has been known that stellar bars in disc galaxies can be triggered by interactions, or by internal processes such as dynamical instabilities. In this work, we explore the differences between these two mechanisms using numerical simulations. We perform two groups of simulations based on isolated galaxies, one group in which a bar develops naturally, and another group in which the bar could not develop in isolation. The rest of the simulations recreate 1:1 coplanar fly-by interactions computed with the impulse approximation. The orbits we use for the interactions represent the fly-bys in groups or clusters of different masses accordingly to the velocity of the encounter. In the analysis, we focus on bars' amplitude, size, pattern speed and their rotation parameter, R = RCR/Rbar. The latter is used to define fast (R < 1.4) and slow rotation (R > 1.4). Compared with equivalent isolated galaxies, we find that bars affected or triggered by interactions: (i) remain in the slow regime for longer, (ii) are more boxy in face-on views and (iii) they host kinematically hotter discs. Within this set of simulations, we do not see strong differences between retrograde or prograde fly-bys. We also show that slow interactions can trigger bar formation. [ABSTRACT FROM AUTHOR]

We present a near-infrared (NIR) imaging study of barred low surface brightness (LSB) galaxies using the TIFR¹ NIR Spectrometer and Imager. LSB galaxies are dark matter dominated, late-type spirals that have low-luminosity stellar discs but large neutral hydrogen (H I) gas discs. Using Sloan Digital Sky Survey images of a very large sample of LSB galaxies derived from the literature, we found that the barred fraction is only 8.3 per cent. We imaged 25 barred LSB galaxies in the J, H, KS wavebands and 29 in the KS band. Most of the bars are much brighter than their stellar discs, which appear to be very diffuse. Our image analysis gives deprojected mean bar sizes of Rb/R25 = 0.40 and ellipticities e ≈ 0.45, which are similar to bars in high surface brightness galaxies. Thus, although bars are rare in LSB galaxies, they appear to be just as strong as bars found in normal galaxies. There is no correlation of Rb/R25 or e with the relative H I or stellar masses of the galaxies. In the (J - KS) colour images most of the bars have no significant colour gradient which indicates that their stellar population is uniformly distributed and confirms that they have low dust content. [ABSTRACT FROM AUTHOR]

In this paper, we use the two-dimensional version of a new analytical gravitational model in order to explore the orbital as well as the escape dynamics of the stars in a barred galaxy composed of a spherically symmetric central nucleus, a bar, a flat disc and a dark matter halo component. A thorough numerical investigation is conducted for distinguishing between bounded and escaping motion. Furthermore, bounded orbits are further classified into nonescaping regular and trapped chaotic using the Smaller ALingment Index method. Our aim is to determine the basins of escape through the two symmetrical escape channels around the Lagrange points L2 and L3 and also to relate them with the corresponding distribution of the escape rates of the orbits.We integrate initial conditions of orbits in several types of planes so as to obtain a more complete view of the overall orbital properties of the dynamical system.We also present evidence that the unstable manifolds which guide the orbits in and out the interior region are directly related with the formation of spiral and ring stellar structures observed in barred galaxies. In particular, we examine how the bar's semimajor axis determines the resulting morphologies. Our numerical simulations indicate that weak barred structures favour the formation of R1 rings or R'1 pseudo-rings, while strong bars on the other hand, give rise to R1R2 and open spiral morphologies. Our results are compared with earlier related work. The escape dynamics and the properties of the manifolds of the full three-dimensional galactic system will be given in an accompanying paper. [ABSTRACT FROM AUTHOR]

Barred galaxies have interesting morphological features whose presence and properties set constraints on galactic evolution. Here we examine barlenses, i.e. lens-like components whose extent along the bar major axis is shorter than that of the bar and whose outline is oval or circular. We identify and analyse barlenses in N-body plus SPH simulations, compare them extensively with those from the NIRS0S (Near-IR S0 galaxy Survey) and the S4G samples (Spitzer Survey of Stellar Structure in Galaxies) and find very good agreement. We observe barlenses in our simulations from different viewing angles. This reveals that barlenses are the vertically thick part of the bar seen face-on, i.e. a barlens seen edge-on is a boxy/peanut/X bulge. In morphological studies, and in the absence of kinematics or photometry, a barlens, or part of it, may be mistaken for a classical bulge. Thus the true importance of classical bulges, both in numbers and mass, is smaller than currently assumed, which has implications for galaxy formation studies. Finally, using the shape of the isodensity curves, we propose a rule of thumb for measuring the barlens extent along the bar major axis of moderately inclined galaxies, thus providing an estimate of which part of the bar is thicker. [ABSTRACT FROM AUTHOR]

The observed velocities of the gas in barred galaxies are a combination of the azimuthally averaged circular velocity and non-circular motions, primarily caused by gas streaming along the bar. These non-circular flows must be accounted for before the observed velocities can be used in mass modelling. In this work, we examine the performance of the tilted-ring method and the DISKFIT algorithm for transforming velocity maps of barred spiral galaxies into rotation curves (RCs) using simulated data. We find that the tilted-ring method, which does not account for streaming motions, under-/overestimates the circular motions when the bar is parallel/perpendicular to the projected major axis. DISKFIT, which does include streaming motions, is limited to orientations where the bar is not aligned with either the major or minor axis of the image. Therefore, we propose a method of correcting RCs based on numerical simulations of galaxies. We correct the RC derived from the tilted-ring method based on a numerical simulation of a galaxy with similar properties and projections as the observed galaxy. Using observations of NGC 3319, which has a bar aligned with the major axis, as a test case, we show that the inferred mass models from the uncorrected and corrected RCs are significantly different. These results show the importance of correcting for the non-circular motions and demonstrate that new methods of accounting for these motions are necessary as current methods fail for specific bar alignments. [ABSTRACT FROM AUTHOR]

We present an analysis of the optical line emission from nearby barred galaxies, and in particular look at the radial range occupied by the bar. In many cases, this region is marked by what we term a 'star formation desert', with a marked deficit of H II regions in optical narrow-band H a imaging. Here we present long-slit spectroscopy revealing that such regions do have line emission, but that it is low-level, spatially smooth and almost ubiquitous. The relative strengths of the H a and the spectrally adjacent [N II] lines in the regions are completely discrepant from those associated with star formation regions, and more closely match expectations for 'LINER' regions. We quantify the total line emission from these extended, kpc-scale regions, and determine the spurious contribution it would make to the determined star formation rate of these galaxies if interpreted as normal H a emission. We concur with previous studies that link this 'LINER' emission to old stellar populations, e.g. post-asymptotic giant branch stars, and propose strongly barred early-type spirals as a prime location for further tests of such emission. [ABSTRACT FROM AUTHOR]

In this paper, we apply a method identified by Puerari & Dottori to find the corotation radii (CR) in spiral galaxies. We apply our method to 57 galaxies, 17 of which have already have their CR locations determined using other methods. The method we adopted entails taking Fourier transforms along radial cuts in the u, g, r, i, and z wavebands and comparing the phase angles as a function of radius between them. The radius at which the phase angles cross indicates the location of the corotation radius. We then calculated the relative bar pattern speed, R, and classified the bar as 'fast', where R < 1.4, slow, where R ≥ 1.4, or intermediate, where the errors on R are consistent with the bar being 'slow' or 'fast'. For the 17 galaxies that had their CR locations previously measured, we found that our results were consistent with the values of R obtained by the computer simulations of Rautiainen, Salo & Laurikainen. For the larger sample, our results indicate that 34 out of 57 galaxies (≃ 60 per cent) have fast bars. We discuss these results in the context of its implications for dark matter concentrations in disc galaxies. We also discuss these results in the context of different models for spiral structure in disc galaxies. [ABSTRACT FROM AUTHOR]

NGC 1097 is a nearby barred spiral galaxy believed to be interacting with the elliptical galaxy NGC 1097A located to its northwest. It hosts a Seyfert 1 nucleus surrounded by a circumnuclear starburst ring. Two straight dust lanes connected to the ring extend almost continuously out to the bar. The other ends of the dust lanes attach to two main spiral arms. To provide a physical understanding of its structural and kinematical properties, two-dimensional hydrodynamical simulations have been carried out. Numerical calculations reveal that many features of the gas morphology and kinematics can be reproduced provided that the gas flow is governed by a gravitational potential associated with a slowly rotating strong bar. By including the self-gravity of the gas disk in our calculation, we have found the starburst ring to be gravitationally unstable, which is consistent with the observation in Hsieh et al. Our simulations show that the gas inflow rate is 0.17Mʘ yr-1 into the region within the starburst ring even after its formation, leading to the coexistence of both a nuclear ring and a circumnuclear disk. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a new method that derives both velocity components in the equatorial plane of a barred stellar disc from the observed line-of-sight velocity, assuming the geometry of a thin disc. The method can be applied to large departures from circular motion, and does not require multipole decomposition. It is based on assumptions that the bar is close to steady state (i.e. does not evolve fast) and that both morphology and kinematics are symmetrical with respect to the major axis of the bar. We derive the equations used in the method and analyse the effect of observational errors on the inferred velocity fields. We show that this method produces meaningful results via a simple schematic model. We also apply the method on integral-field data of NGC 936, for which we recover both velocity components in the disc. Knowing both velocity components in the disc, i.e. the non-observable transverse velocity in addition to the line-of-sight velocity, puts additional constraints on dynamical models and allows for new ways of determining parameters that are crucial in characterizing galaxies. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the accuracy in the recovery of the stellar dynamics of barred galaxies when using axisymmetric dynamical models. We do this by trying to recover the mass-to-light ratio ( M/ L) and the anisotropy of realistic galaxy simulations using the Jeans Anisotropic Multi-Gaussian Expansion (JAM) modelling method. However, given that the biases we find are mostly due to an application of an axisymmetric modelling algorithm to a non-axisymmetric system and in particular to inaccuracies in the deprojected mass model, our results are relevant for general axisymmetric modelling methods. We run N-body collisionless simulations to build a library with various luminosity distribution, constructed to mimic real individual galaxies, with realistic anisotropy. The final result of our evolved library of simulations contains both barred and unbarred galaxies. The JAM method assumes an axisymmetric mass distribution, and we adopt a spatially constant M/ L and anisotropy distributions. The models are fitted to two-dimensional maps of the second velocity moments of the simulations for various viewing angles [position angle (PA) of the bar and inclination of the galaxy]. We find that the inclination is generally well recovered by the JAM models, for both barred and unbarred simulations. For unbarred simulations the M/ L is also accurately recovered, with negligible median bias and with a maximum one of just Δ( M/ L) < 1.5 per cent when the galaxy is not too close to face on. At very low inclinations () the M/ L can be significantly overestimated (9 per cent in our tests, but errors can be larger for very face-on views). This is in agreement with previous studies. For barred simulations the M/ L is on average (when PA = 45°) essentially unbiased, but we measure an over/underestimation of up to Δ( M/ L) = 15 per cent in our tests. The sign of the M/ L bias depends on the PA of the bar as expected: overestimation occurs when the bar is closer to end-on, due to the increased stellar motion along the line-of-sight, and underestimation otherwise. For unbarred simulations, the JAM models are able to recover the mean value of the anisotropy with bias , within the region constrained by the kinematics. However when a bar is present, or for nearly face-on models, the recovered anisotropy varies wildly, with biases up to Δβ z≈ 0.3. [ABSTRACT FROM AUTHOR]

We investigate the dependence of the occurrence of bars in galaxies on galaxy properties and environment. We use a volume-limited sample of 33,391 galaxies brighter than Mr = -19.5 + 5logh at 0.02 ≤ z ≤ 0.05489, drawn from the Sloan Digital Sky Survey Data Release 7. We classify the galaxies into early and late types, and identify bars by visual inspection. Among 10,674 late-type galaxies with axis ratio b/a > 0.60, we find 3240 barred galaxies (fbar = 30.4%) which divide into 2542 strong bars (fSB1 = 23.8%) and 698 weak bars (fSB2 = 6.5%). We find that fSB1 increases as u - r color becomes redder and that it has a maximum value at intermediate velocity dispersion (σ ≃ 150 km s-1). This trend suggests that strong bars are dominantly hosted by intermediate-mass systems. Weak bars prefer bluer galaxies with lower mass and lower concentration. In the case of strong bars, their dependence on the concentration index appears only for massive galaxies with σ > 150 km s-1. We also find that fbar does not directly depend on the large-scale background density when other physical parameters (u - r color or σ) are fixed. We discover that fSB1 decreases as the separation to the nearest neighbor galaxy becomes smaller than 0.1 times the virial radius of the neighbor regardless of neighbor's morphology. These results imply that strong bars are likely to be destroyed during strong tidal interactions and that the mechanism for this phenomenon is gravitational and not hydrodynamical. The fraction of weak bars has no correlation with environmental parameters. We do not find any direct evidence for environmental stimulation of bar formation. [ABSTRACT FROM AUTHOR]

In this paper we present building blocks which can explain the formation and properties both of spirals and of inner and outer rings in barred galaxies. We first briefly summarize the main results of the full theoretical description we have given elsewhere, presenting them in a more physical way, aimed to an understanding without the requirement of extended knowledge of dynamical systems or of orbital structure. We introduce in this manner the notion of manifolds, which can be thought of as tubes guiding the orbits. The dynamics of these manifolds can govern the properties of spirals and of inner and outer rings in barred galaxies. We find that the bar strength affects how unstable the L1 and L2 Lagrangian points are, the motion within the manifold tubes and the time necessary for particles in a manifold to make a complete turn around the galactic centre. We also show that the strength of the bar, or, to be more precise, of the non-axisymmetric forcing at and somewhat beyond the corotation region, determines the resulting morphology. Thus, less strong bars give rise to R1 rings or pseudo-rings, while stronger bars drive and spiral morphologies. We examine the morphology as a function of the main parameters of the bar and present descriptive two-dimensional plots to that avail. We also derive how the manifold morphologies and properties are modified if the L1 and L2 Lagrangian points become stable. Finally, we discuss how dissipation affects the manifold properties and compare the manifolds in gas like and in stellar cases. Comparison with observations as well as clear predictions to be tested by observations will be given in an accompanying paper. [ABSTRACT FROM AUTHOR]

We have modelled 38 barred galaxies by using near-infrared and optical data from the Ohio State University Bright Spiral Galaxy Survey. We constructed the gravitational potentials of the galaxies from H-band photometry, assuming a constant mass-to-light ratio. The halo component we choose corresponds to the so-called universal rotation curve. In each case, we used the response of gaseous and stellar particle disc to rigidly rotating potential to determine the pattern speed. We find that the pattern speed of the bar depends roughly on the morphological type. The average value of corotation resonance radius to bar radius, , increases from 1.15 ± 0.25 in types SB0/a–SBab to 1.44 ± 0.29 in SBb and 1.82 ± 0.63 in SBbc–SBc. Within the error estimates for the pattern speed and bar radius, all galaxies of type SBab or earlier have a fast bar , whereas the bars in later type galaxies include both fast and slow rotators. Of 16 later type galaxies with a nominal value of , there are five cases, where the fast-rotating bar is ruled out by the adopted error estimates. We also study the correlation between the parameter and other galactic properties. The clearest correlation is with the bar size: the slowest bars are also the shortest bars when compared to the galaxy size. A weaker correlation is seen with bar strength in a sense that slow bars tend to be weaker. These correlations leave room for a possibility that the determined pattern speed in many galaxies corresponds to actually that of the spiral, which rotates more slowly than the bar. No clear correlation is seen with either the galaxy luminosity or the colour. [ABSTRACT FROM AUTHOR]

I present the results of multicomponent decomposition of V and R broad-band images of a sample of 17 nearby galaxies, most of them hosting bars and active galactic nuclei (AGN). I usebudda v2.1 to produce the fits, allowing the inclusion of bars and AGN in the models. A comparison with previous results from the literature shows a fairly good agreement. It is found that the axial ratio of bars, as measured from ellipse fits, can be severely underestimated if the galaxy axisymmetric component is relatively luminous. Thus, reliable bar axial ratios can only be determined by taking into account the contributions of bulge and disc to the light distribution in the galaxy image. Through a number of tests, I show that neglecting bars when modelling barred galaxies can result in an overestimation of the bulge-to-total luminosity ratio of a factor of 2. Similar effects result when bright, type 1 AGN are not considered in the models. By artificially redshifting the images, I show that the structural parameters of more distant galaxies can in general be reliably retrieved through image fitting, at least up to the point where the physical spatial resolution is ≈1.5 kpc. This corresponds, for instance, to images of galaxies at with a seeing full width at half-maximum (FWHM) of 1.5 arcsec, typical of the Sloan Digital Sky Survey (SDSS). In addition, such a resolution is also similar to what can be achieved with the Hubble Space Telescope ( HST), and ground-based telescopes with adaptive optics, at . Thus, these results also concern deeper studies such as COSMOS and SINS. This exercise shows that disc parameters are particularly robust, but bulge parameters are prone to errors if its effective radius is small compared to the seeing radius, and might suffer from systematic effects. For instance, the bulge-to-total luminosity ratio is systematically overestimated, on average, by 0.05 (i.e. 5 per cent of the galaxy total luminosity). In this low-resolution regime, the effects of ignoring bars are still present, but AGN light is smeared out. I briefly discuss the consequences of these results to studies of the structural properties of galaxies, in particular on the stellar mass budget in the local Universe. With reasonable assumptions, it is possible to show that the stellar content in bars can be similar to that in classical bulges and elliptical galaxies. Finally, I revisit the cases of NGC 4608 and 5701 and show that the lack of stars in the disc region inside the bar radius is significant. Accordingly, the best-fitting model for the former uses a Freeman type II disc. [ABSTRACT FROM AUTHOR]

We have obtained deep J and Ks images of a sample of nine barred galaxies in order to collect a reliable and homogeneous set of images to which N-body simulations of barred galaxies will be compared. The observations were performed using the new near-infrared camera available at the 2.1-m telescope of the Observatorio Astrofísico Guillermo Haro (OAGH) in Cananea, Sonora, Mexico. We present the results of surface photometry techniques applied to the observed images, as well as to the deprojected images. These results include radial profiles of surface brightness (elliptically averaged), colour, position angle, ellipticity and the b4 Fourier component. In addition, we present isophotal maps, colour maps, surface brightness profiles along the bar major and minor axes, characteristic radial scalelengths and bar length estimates. We discuss how projection effects can influence these measurements and the uncertainties introduced by deprojecting galaxy images. We show that analytical expressions can be used to obtain reliable estimates of deprojected bar lengths, ellipticities and position angles directly from the observed images. These expressions are based on the assumption that the outer parts of the bar are vertically thin, as shown by theoretical work. The usefulness of our data in addressing issues on bar formation and evolution is also discussed. In particular, we present results showing a steep drop in the ellipticity profile, as expected for bar formation processes in which the dark matter halo plays a fundamental role. Furthermore, we show that the location of this drop is a good indicator of the end of the bar in strongly barred galaxies, as predicted by numerical models. [ABSTRACT FROM AUTHOR]

We study the orbital structure of a self-consistent N-body equilibrium configuration of a barred galaxy constructed from cosmological initial conditions. The value of its spin parameter λ is near the observed value of our Galaxy . We classify the orbits in regular and chaotic using a combination of two different methods and find 60 per cent of them to be chaotic. We examine the phase space using projections of the 4D surfaces of section for test particles as well as for real N-body particles. The real particles are not uniformly distributed in the whole phase space but they avoid orbits that do not support the bar. We use frequency analysis for the regular orbits as well as for the chaotic ones to classify certain types of orbits of our self-consistent system. We find the main resonant orbits and their statistical weight in supporting the shape of the bar, and we emphasize the role of weakly chaotic orbits in supporting the boxiness at the end of the bar. [ABSTRACT FROM AUTHOR]

Despite the increasing number of studies of barred galaxies at intermediate and high redshifts, double-barred (S2B) systems have only been identified in the nearby universe thus far. In this feasibility study, we demonstrate that the detection and analysis of S2Bs is possible at intermediate redshifts with the exquisite resolution of the Hubble Space Telescope Advanced Camera for Surveys ( HST/ACS). We identify barred galaxies in the HST/ACS data of the Great Observatories Origins Deep Survey (GOODS) using a novel method. The radial profile of the Gini coefficient – a model-independent structure parameter – is able to detect bars in early-type galaxies that are large enough that they might host an inner bar of sufficient angular size. Using this method and subsequent examination with unsharp masks and ellipse fits, we identified the two most distant S2Bs currently known (at redshifts and 0.148). We investigate the underlying stellar populations of these two galaxies through a detailed colour analysis, in order to demonstrate the analysis that could be performed on a future sample of intermediate-redshift S2Bs. We also identify two S2Bs and five S2B candidates in the HST/ACS data of the Cosmic Evolution Survey (COSMOS). Our detections of distant S2Bs show that deep surveys like GOODS and COSMOS have the potential to push the limit for S2B detection and analysis out by a factor of 10 in redshift and look-back time compared to the previously known S2Bs. This in turn would provide new insight into the formation of these objects. [ABSTRACT FROM AUTHOR]

I present a study of the sizes (semimajor axes) of bars in disc galaxies, combining a detailed R-band study of 65 S0–Sb galaxies with the B-band measurements of 70 Sb–Sd galaxies from Martin (1995) . As has been noted before with smaller samples, bars in early-type (S0–Sb) galaxies are clearly larger than bars in late-type (Sc–Sd) galaxies; this is true both for relative sizes (bar length as fraction of isophotal radius R25 or exponential disc scalelength h) and absolute sizes (kpc). S0–Sab bars extend to and . Late-type bars extend to only and 0.2–1.5 h; their mean sizes are and . Sb galaxies resemble earlier-type galaxies in terms of bar size relative to h; their smaller R25-relative sizes may be a side effect of higher star formation, which increases R25 but not h. Sbc galaxies form a transition between the early- and late-type regimes. For S0–Sbc galaxies, bar size correlates well with disc size (both R25 and h); these correlations are stronger than the known correlation with . All correlations appear to be weaker or absent for late-type galaxies; in particular, there seems to be no correlation between bar size and either h or for Sc–Sd galaxies. Because bar size scales with disc size and galaxy magnitude for most Hubble types, studies of bar evolution with redshift should select samples with similar distributions of disc size or magnitude (extrapolated to present-day values); otherwise, bar frequencies and sizes could be mis-estimated. Because early-type galaxies tend to have larger bars, resolution-limited studies will preferentially find bars in early-type galaxies (assuming no significant differential evolution in bar sizes). I show that the bars detected in Hubble Space Telescope ( HST) near-infrared(IR) images at by Sheth et al. have absolute sizes consistent with those in bright, nearby S0–Sb galaxies. I also compare the sizes of real bars with those produced in simulations and discuss some possible implications for scenarios of secular evolution along the Hubble sequence. Simulations often produce bars as large as (or larger than) those seen in S0–Sb galaxies, but rarely any as small as those in Sc–Sd galaxies. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the dynamical effects of an interaction between an initially barred galaxy and a small spherical companion using an N-body/smoothed-particle-hydrodynamics algorithm. In the models described here the small companion passes through the disc of the larger galaxy nearly perpendicular to its plane. The impact positions and times are varied with respect to the phase of the bar and the dynamical evolution of the disc. The interactions produce expanding ring structures, offset bars, spokes and other asymmetries in the stars and gas. These characteristic signatures of the interaction are present in the disc for about 1 Gyr. We find that in some cases it is possible to destroy the bar while keeping the disc structure. In general, the central impacts cause larger damage to the bar and the disc than the peripheral ones. The interaction tends to accelerate the transition from a strongly-barred galaxy to a weakly- or non-barred galaxy. The final disc morphology is determined more by the impact position relative to the bar rather than the impact time. [ABSTRACT FROM AUTHOR]

It is assumed that the two-fold disc-wide symmetry of spirals is caused by density waves, but also the potential of a bar component may have a significant influence on structural properties. The strength of the bar component appears to be anti-correlated with the degree of symmetry of star-forming regions in the spiral arms (Rozas et al., 1998). We present new results of R and Hα surface photometry of a sample of bright barred spirals. A photometric decompositon of the galaxy components is carried out in order to make a more accurate measurement of the strength of the bar and its interrelation to gas and stars in the disc. [ABSTRACT FROM AUTHOR]

ABSTRACT We have studied the formation of complex central structures in barred galaxies – nested bars, nuclear spirals and circumnuclear rings – by making N -body simulations, which include the gas component as inelastically colliding particles. Our models suggest that many of the observed features in both the stellar and gas components can be explained by the dynamical effect of two or more modes in the stellar disc. Especially, many morphological features in our simulations correspond to analytically studied orbit loops in double-barred potentials. Interestingly, a fast-rotating secondary bar forms in a purely stellar disc in our simulations, which disagrees with some previous studies where the presence of a dissipative component was needed. [ABSTRACT FROM AUTHOR]

Abstract Boxy edge-on profiles can be accounted for not only in models of barred galaxies, but also in models of normal (non-barred) galaxies. Thus the presence of a bar is not a sine qua non condition for the appearance of this feature, as often assumed. We show that a ‘boxy’ or a ‘peanut’ structure in the central parts of a model is due to the presence of vertical resonances at which stable families of periodic orbits bifurcate from the planar x1 family. The orbits of these families reach in their projections on the equatorial plane a maximum distance from the centre, beyond which they increase their mean radii by increasing only their deviations from the equatorial plane. The resulting orbital profiles are ‘stair-type’ and constitute the backbone for the observed boxy structures in edge-on views of N-body models and, we believe, in edge-on views of disc galaxies. Since the existence of vertical resonances is independent of barred or spiral perturbations in the disc, ‘boxy’ profiles may appear also in almost axisymmetric cases. [ABSTRACT FROM AUTHOR]

Cloud collision has been proposed as a way to link the small-scale star formation process with the observed global relation between the surface star formation rate and gas surface density. We suggest that this model can be improved further by allowing the productivity of such collisions to depend on the relative velocity of the two clouds. Our adjustment implements a simple step function that results in the most successful collisions being at the observed velocities for triggered star formation. By applying this to a high-resolution simulation of a barred galaxy, we successfully reproduce the observational result that the star formation efficiency (SFE) in the bar is lower than that in the spiral arms. This is not possible when we use an efficiency dependent on the internal turbulence properties of the clouds. Our results suggest that high-velocity collisions driven by the gravitational pull of the clouds are responsible for the low bar SFE. [ABSTRACT FROM PUBLISHER]