Two-dimensional spectroscopy of double-barred galaxies

We describe the results of our spectroscopy for a sample of barred galaxies whose inner regions exhibit an isophotal twist commonly interpreted as a secondary bar. The line-of-sight velocity fields of the ionized gas and stars and the light-of-sight velocity dispersion fields of the stars were constructed from two-dimensional spectroscopy with the 6-m Special Astrophysical Observatory telescope. We detected various types of noncircular motions of ionized gas: radial flows within large-scale bars, counterrotation of the gas and stars at the center of NGC 3945, a polar gaseous disk in NGC 5850, etc. Our analysis of the optical and near-infrared galaxy images (both ground-based and those from the Hubble Space Telescope) revealed circumnuclear minispirals in five objects. The presence of an inner (secondary) bar in the galaxy images is shown to have no effect on the circumnuclear kinematics of the gas and stars. Thus, contrary to popular belief, the secondary bar is not a dynamically decoupled galactic structure. We conclude that the so-called double-barred galaxies are not a separate type of galaxy but are a combination of objects with distinctly different morphologies of their circumnuclear regions.     

Diagnostics of Ionized Gas in Galaxies with the “BPT–Radial Velocity Dispersion” Relation

In order to study the state of gas in galaxies, diagrams of the relation of optical emission line fluxes are used allowing one to separate main ionization sources: young stars in the HII regions, active galactic nuclei, and shock waves. In the intermediate cases, for example, when the contributions of radiation from OB stars and from shock waves mix, identification becomes uncertain, and the issue remains unresolved on what determines the observed state of the diffuse ionized gas (DIG) including the one on large distances fromthe galactic plane. Adding of an extra parameter—the gas velocity dispersion in the line-of-sight—to classical diagnostic diagrams helps to find a solution. In the present paper, we analyze the observed data for several nearby galaxies: for UGC10043 with the galactic wind, for the dwarf galaxies VIIZw403 andMrk 35 with star formation, for the galaxy Arp 212 with a polar ring. The data on the velocity dispersion are obtained at the 6-m SAO RAS telescope with the Fabry-Perot scanning interferometer, the information on the relation of main emission-line fluxes–from the published results of the integral-field spectroscopy (the CALIFA survey and the MPFS spectrograph). A positive correlation between the radial velocity dispersion and the contribution of shock excitation to gas ionization are observed. In particular, in studying Arp 212, our approach allowed us to confirm the assumption on a direct collision of gaseous clouds on the inclined orbits with the main disk of the galaxy.     

Study of the structure and kinematics of the NGC 7465/64/63 triplet galaxies

We analyze new observational data obtained at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with the multimode SCORPIO instrument and the Multi-Pupil Fiber Spectrograph for the group of galaxies NGC 7465/64/63. For one of the group members (NGC 7465), the presence of a polar ring has been suspected. We have constructed the large-scale brightness distributions, the ionized-gas velocity and velocity dispersion fields for all three galaxies as well as the line-of-sight velocity curves based on emission and absorption lines and the stellar velocity field in the central region for NGC 7465. As a result of our analysis of the data obtained, we have discovered an inner stellar disk (r ?? 0.5 kpc) and a warped gaseous disk in NGC 7465, in addition to the main stellar disk. Based on a joint study of our photometric and spectroscopic data, we have established that NGC 7464 is an irregular IrrI-type galaxy whose structural and kinematic peculiarities most likely resulted from its gravitational interaction with NGC 7465. The velocity field of the ionized gas in NGC 7463 turns out to be typical of barred spiral galaxies, and the warp of the outer parts of its disk could arise from a close encounter with one of the galaxies of the environment.     

Warped polar ring in the Arp 212 galaxy

The Fabry-Perot scanning interferometer mounted on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences is used to study the distribution and kinematics of ionized gas in the peculiar galaxy Arp 212 (NGC 7625, IIIZw 102). Two kinematically distinct subsystems—the inner disk and outer emission filaments—are found within the optical radius of the galaxy. The first subsystem, at galactocentric distances r < 3.5 kpc, rotates in the plane of the stellar disk. The inner part of the ionized-gas disk (r<1.5–2 kpc) exactly coincides with the previously known disk consisting of molecular gas. The second subsystem of ionized gas is located at galactocentric distances 2–6 kpc. This subsystem rotates in a plane tilted by a significant angle to the stellar disk. The angle of orbital inclination in the outer disk increases with galactocentric distance and reaches 50° at r ≈ 6 kpc. The ionized fraction of the gaseous disk does not show up beyond this galactocentric distance, but we believe that the HI disk continues to warp and approaches the plane that is polar with respect to the inner disk of the galaxy. Hence Arp 212 can be classified as a galaxy with a polar ring (or a polar disk). The observed kinematics of the ionized and neutral gas can be explained assuming that the distribution of gravitational potential in the galaxy is not spherically symmetric. Most probably, the polar ring have formed via accretion of gas from the dwarf satellite galaxy UGC 12549.     

Spiral-Vortex Structure in the Gaseous Disks of Galaxies

General ideas, as well as experimental and theoretical efforts concerning the prediction and discovery of new structures in the disks of spiral galaxies – giant anticyclones - are reviewed. A crucial point is the development of a new method to restore the full vector velocity field of the galactic gas from the line-of-sight velocity field. This method can be used to get self-consistent solutions for the following problems: 1) determination of non-circular velocities associated with spiral-vortex structure; 2) determination of fundamental parameters of this structure: pattern speed, corotation radius, location of giant anticyclones; 3) refinement of galactic rotation curves taking into account regular non-circular motion in the spiral density wave, which makes it possible to build more accurate models of the mass distribution in the galaxy; 4) refinement of parameters of the rotating gaseous disk: inclination angle, center of rotation and position angle of the major dynamical axis, systematic velocity. The method is demonstrated using the restoration of the velocity field of the galaxy NGC 157 as an example. Results for this and some other spiral galaxies suggest that giant anticyclones are a universal property of galaxies with grand design structure.     

Kinematics of Gas and Stars in 20 Disc Galaxies

In this paper we present the kinematics of the gas and/or the stars of a sample of 20 disc galaxies. We investigate whether there is any relation between the kinematics of the gas and stars and the classical morphological type of the galaxies in the sample. We deduce that, in most of the late-type spirals we have studied, the stars and the ionized gas are moving with virtually circular velocity, except when the spectroscopic slit crosses a bar region. On the other hand, we found in the central parts of early-type disc galaxies a wider variety of different behaviour of stars and gas. We find many possible factors that complicate the classification of the kinematical properties of the galaxies by their morphological type: the presence of counter-rotations (star vs. stars or star vs. gas), misalignment between the different kinematic components present in the galaxy, the presence of a bar structure and its orientation with respect to the line of nodes of the galaxy, and interactions and mergers or external accretion processes are some of the problems we find in the study of the kinematics of a galaxy.     

Ionized gas rotation curves in nearby dwarf galaxies

We present the results of study of the ionized gas velocity fields in 28 nearby (systemic velocity below 1000 km s^?1) dwarf galaxies. The observations were made at the 6-m BTA telescope of the SAO RAS with the scanning Fabry-Perot interferometer in the Hα emission line. We were able to measure regular circular rotation parameters in 25 galaxies. As a rule, rotation velocities measured in HII are in a good agreement with the data on the HI kinematics at the same radii. Three galaxies reveal position angles of the kinematic axis in the HII velocity fields that strongly (tens of degrees) differ from the measurements in neutral hydrogen at large distances from the center or from the orientation of the major axis of optical isophotes. The planes of the gaseous and stellar disks in these galaxies most likely do not coincide. Namely, in DDO99 the gaseous disk is warped beyond the optical radius, and in UGC3672 and UGC8508 the inclination of orbits of gas clouds varies in the inner regions of galaxies. It is possible that the entire ionized gas in UGC8508 rotates in the plane polar to the stellar disk.     

Observational study of UGC 4892—a candidate for polar-ring galaxies

We present the results of photometric and spectroscopic observations of UGC 4892—a candidate for polar-ring galaxies. We show that the feature in the brightness distribution described by Whitmore et al. (1990) as a possible polar ring is actually a companion galaxy that interacts with the giant main galaxy. The velocity fields of the gas and stellar components can be explained by assuming that the gas lost by the companion galaxy and captured by the main galaxy forms a gaseous stream rotating around the latter in a plane almost perpendicular to its principal plane.     

2D spectroscopy of candidate polar-ring galaxies: I. The pair of galaxies UGC 5600/09

Observations of the pair of galaxies VV 330 with the SCORPIO multimode instrument on the 6-m Special Astrophysical Observatory telescope are presented. Large-scale velocity fields of the ionized gas in Hα and brightness distributions in continuum and Hα have been constructed for both galaxies with the help of a scanning Fabry-Perot interferometer. Long-slit spectroscopy is used to study the stellar kinematics. Analysis of the data obtained has revealed a complex structure in each of the pair components. Three kinematic subsystems have been identified in UGC 5600: a stellar disk, an “inner gas ring” turned with respect to the disk through ～80°, and an outer gas disk. The stellar and outer gas disks are noncoplanar. Possible scenarios for the formation of the observed multicomponent kinematic galactic structure are considered, including the case where the large-scale velocity field of the gas is represented by the kinematic model of a disk with a warp. The velocity field in the second galaxy of the pair, UGC 5609, is more regular. A joint analysis of the data on the photometric structure and the velocity field has shown that this is probably a late-type spiral galaxy whose shape is distorted by the gravitational interaction, possibly, with UGC 5600.     

PGC 60020: a polar-ring galaxy

We present an analysis of new observations of a peculiar galaxy PGC60020, obtained with the 6-m BTA telescope of the SAO RAS with a multimode SCORPIO instrument. The observational data includes direct images in the B, V, R _c photometric bands and long-slit spectra in the red range (the H?? line spectral region). Based on the analysis of these data it was found that PGC60020 belongs to the type of classical polar-ring galaxies. Its main body is an S0 galaxy, around the major axis of which a disk of gas, dust and stars is rotating in the plane inclined at an angle of about 60° to the galactic plane. A loop-shaped structure stretches from the southern part of this disk (possibly, a tidal tail) towards the SDSS J 171745.58+404137.1 galaxy.     

Supersonic motions of galaxies in clusters

We study motions of galaxies in galaxy clusters formed in the concordance Λ cold dark matter cosmology. We use high-resolution cosmological simulations that follow the dynamics of dark matter and gas and include various physical processes critical for galaxy formation: gas cooling, heating and star formation. Analysing the motions of galaxies and the properties of intracluster gas in a sample of eight simulated clusters at z = 0, we study the velocity dispersion profiles of the dark matter, gas and galaxies. We measure the mean velocity of galaxy motions and gas sound speed as a function of radius and calculate the average Mach number of galaxy motions. The simulations show that galaxies, on average, move supersonically with the average Mach number of ≈1.4, approximately independent of the cluster-centric radius. The supersonic motions of galaxies may potentially provide an important source of heating for the intracluster gas by driving weak shocks and via dynamical friction, although these heating processes appear to be inefficient in our simulations. We also find that galaxies move slightly faster than the dark matter particles. The magnitude of the velocity bias,   b _v ≈ 1.1  , is, however, smaller than the bias estimated for subhaloes in dissipationless simulations. Interestingly, we find velocity bias in the tangential component of the velocity dispersion, but not in the radial component. Finally, we find significant random bulk motions of gas. The typical gas velocities are of order ≈20–30 per cent of the gas sound speed. These random motions provide about 10 per cent of the total pressure support in our simulated clusters. The non-thermal pressure support, if neglected, will bias measurements of the total mass in the hydrostatic analyses of the X-ray cluster observations.     

The relative orientation of the accretion disk and host galaxy disk in Seyferts

We present the results of the study of the orientation of the accretion disk relative to the host galaxy disk in Seyfert galaxies. We used a sample selected by a mostly isotropic property, the flux at 60 μm, with radio and optical data homogeneously observed and analyzed, to avoid selection effects. We found that the observed i and δ values, galaxy inclination and difference between the position angle of the jet and the galaxy major axis, respectively, are consistent with a random β-distribution, the angle between the jet and the galaxy plane axis. We also found that the previously suggested Zone of Avoidance disappears and was probably due to a selection effect. We suggest several explanations for the misalignment of the accretion disk relative to the galaxy disk.     

Gas motions in the plane of the spiral galaxy NGC 3631

The velocity field of the nearly face-on galaxy NGC 3631, derived from observations in the H α line and H  i radio line, is analysed to study perturbations related to the spiral structure of the galaxy. We confirm our previous conclusion that the line-of-sight velocity field gives evidence of the wave nature of the observed two-armed spiral structure. Fourier analysis of the observed velocity field is used to determine the location of corotation of the spiral structure of this galaxy, and the radius of corotation R _c is found to be about 42 arcsec, or 3.2 kpc. The vector velocity field of the gas in the plane of the disc is restored, and, taking into account that we previously investigated vertical motions, we now have a full three-dimensional gaseous velocity field of the galaxy. We show clear evidence of the existence of two anticyclonic and four cyclonic vortices near corotation in a frame of reference rotating with the spiral pattern. The centres of the anticyclones lie between the observed spiral arms. The cyclones lie close to the observed spirals, but their centres are shifted from the maxima in brightness.     

Modelling gaseous and stellar kinematics in the disc galaxies NGC 772, 3898 and 7782

We present V -band surface photometry and major-axis kinematics of stars and ionized gas of three early-type spiral galaxies, namely NGC 772, 3898 and 7782. For each galaxy we present a self-consistent Jeans model for the stellar kinematics, adopting the light distribution of bulge and disc derived by means of a two-dimensional parametric photometric decomposition. This allows us to investigate the presence of non-circular gas motions, and derive the mass distribution of luminous and dark matter in these objects.
NGC 772 and 7782 have apparently normal kinematics with the ionized gas tracing the gravitational equilibrium circular speed. This is not true in the innermost region (| r |≲8 arcsec) of NGC 3898, where the ionized gas is rotating more slowly than the circular velocity predicted by dynamical modelling. This phenomenon is common in the bulge-dominated galaxies for which dynamical modelling enables us to make the direct comparison between the gas velocity and the circular speed, and it poses questions about the reliability of galaxy mass distributions derived by the direct decomposition of the observed ionized-gas rotation curve into the contributions of luminous and dark matter.     

The hierarchical origin of galaxy morphologies

We report first results from a series of N-body/gasdynamical simulations designed to study the origin of galaxy morphologies in a cold dark matter-dominated universe. The simulations include star formation and feedback and have numerical resolution sufficiently high to allow for a direct investigation of the morphology of simulated galaxies. We find, in agreement with previous theoretical work, that the presence of the main morphological components of galaxies—disks, spheroids, bars—is regulated by the mode of gas accretion and intimately linked to discrete accretion events. In the case we present, disks arise from the smooth deposition of cooled gas at the center of dark halos, spheroids result from the stirring of preexisting disks during mergers, and bars are triggered by tides generated by satellites. This demonstrates that morphology is a transient phenomenon within the lifetime of a galaxy and that the Hubble sequence reflects the varied accretion histories of galaxies in hierarchical formation scenarios. In particular, we demonstrate directly that disk/bulge systems can be built and rebuilt by the smooth accretion of gas onto the remnant of a major merger and that the present-day remnants of late dissipative mergers between disks are spheroidal stellar systems with structure resembling that of field ellipticals. The perplexing variety of galaxy morphologies is thus highly suggestive of—and may actually even demand—a universe where structures have evolved hierarchically.     

Kinematics and stellar disk modeling of lenticular galaxies

We present the results of spectroscopic observations of three S0-Sa galaxies: NGC 338, NGC 3245, and NGC 5440 at the SAO RAS 6-m BTA telescope. The radial distributions of the line-ofsight velocities and radial velocity dispersions of stars and ionized gas were obtained, and rotation curves of galaxies were computed. We construct the numerical dynamic N-body galaxy models with N ?? 10⁶ points. The models include three components: a ??live?? bulge, a collisionless disk, dynamically evolving to the marginally stable state, and a pseudo-isothermal dark halo. The estimates of radial velocities and velocity dispersions of stars obtained from observations are compared with model estimates, projected onto the line of sight. We show that the disks of NGC 5440 and the outer regions of NGC 338 are dynamically overheated. Taking into account the previously obtained observations, we conclude that the dynamic heating of the disk is present in a large number of early-type disk galaxies, and it seems to ensue from the external effects. The estimates of the disk mass and relative mass of the dark halo are given, as well as the disk mass-to-luminosity ratio for seven galaxies, observed at the BTA.     

The phenomenon of the galaxy NGC 6286: A forming polar ring or a superwind?

We present our observations of the pair of interacting galaxies NGC 6285/86 carried out with the 6-m Special Astrophysical Observatory (SAO) telescope using 1D and 2D spectroscopy. The observations of NGC 6286 with a long-slit spectrograph (UAGS) near the Hα line revealed the rotation of the gaseous disk around an axis offset by 5″–7″ from the photometric center and a luminous gas at a distance up to 9 kpc in a direction perpendicular to the galactic plane. Using a multipupil fiber spectrograph (MPFS), we constructed the velocity fields of the stellar and gaseous components in the central region of this galaxy, which proved to be similar. The close radial velocities of the pair and the wide (5′×5′) field of view of the scanning Fabry-Perot interferometer (IFP) allowed us to simultaneously obtain images in the Hα and [N II]λ6583 lines and in the continuum, as well as to construct the radial velocity fields and to map the distribution of the [N II]λ6583/Hα ratio for both galaxies. Based on all these data, we studied the gas kinematics in the galaxies, constructed their rotation curves, and estimated their masses (2 × 10¹¹M_⊙ for NGC 6286 and 1.2 × 10¹⁰M_⊙ for NGC 6285). We found no evidence of gas rotation around the major axis of NGC 6286, which argues against the assumption that this galaxy has a forming polar ring. The IFP observations revealed an emission nebula around this galaxy with a structure characteristic of superwind galaxies. The large [N II]λ6583/Hα ratio, which suggests the collisional excitation of its emission, and the high infrared luminosity are additional arguments for the hypothesis of a superwind in the galaxy NGC 6286. A close encounter between the two galaxies was probably responsible for the starburst and the bipolar outflow of hot gas from the central region of the disk.     

Effects of data incompleteness on the results of Fourier analysis of line-of-sight velocity fields in spiral-galaxy disks

Our main goal is to investigate the effects of data incompleteness on the results of Fourier analysis of line-of-sight velocity fields in the disks of spiral galaxies. We have carried out a number of numerical experiments, first with an artificially created simple velocity field and then with the velocity fields of two real galaxies, which qualitatively differ in data filling: NGC 157 and NGC 3631 with good and bad data filling, respectively. The field of purely circular velocities is chosen as the simplest artificial velocity field, because the circular velocities of spiral galaxies are much high than the residual (noncircular) velocities. Superimposing a “mask” simulating blank spots (holes) in the map of observational data on this artificial field has no effect on the results of Fourier analysis of this simplest field. A similar result is obtained for real galaxies with good data filling of the observed velocity fields. Superimposing arbitrarily shaped masks on the observed velocity field of NGC 157 in such a way that the field was filled by a mere 50% (at each radius) could not change appreciably the radial variations of large-scale Fourier harmonics. The situation qualitatively changes in attempting to fill the holes in the observed velocity field of NGC 3631 in some way. When missing velocities are artificially introduced by using the simplest model of purely circular gas rotation, the amplitudes and phases of the principal Fourier harmonics are distorted. In particular, a substantial distortion of the third harmonic also causes an increase in the error when determining the corotation radius from data of the filled field. When the filling of the velocity field is increased by degrading the spatial resolution, the amplitudes of most harmonics decrease throughout the entire disk region; as a result, their radial variations are smoothed out and the behavior of harmonic phases in the range of moderately high initial amplitudes can be distorted. An abnormal enhancement of the highest Fourier harmonics in the regions of low filling of the initial field is also possible. At the same time, despite the above distortions, the corotation radius determined from the smoothed fields matches that for the initial velocity fields.     

Variation of bar strength with central velocity dispersion in spiral galaxies

We investigate the variation of bar strength with central velocity dispersion in a sample of barred spiral galaxies. The bar strength is characterized by Q _g , the maximal tangential perturbation associated with the bar, normalized by the mean axisymmetric force. It is derived from the galaxy potentials which are obtained using near-infrared images of the galaxies. However, Q _g is sensitive to bulge mass. Hence we also estimated bar strengths from the relative Fourier intensity amplitude (A ₂) of bars in near-infrared images. The central velocity dispersions were obtained from integral field spectroscopy observations of the velocity fields in the centers of these galaxies; it was normalized by the rotation curve amplitude obtained from HI line width for each galaxy. We found a correlation between bar strengths (both Q _g and A ₂) and the normalized central velocity dispersions in our sample. This suggests that bars weaken as their central components become kinematically hotter. This may have important implications for the secular evolution of barred galaxies.     

Compact groups in theory and practice – II. Comparing the observed and predicted nature of galaxies in compact groups

We examine the properties of galaxies in compact groups (CGs) identified in a mock galaxy catalogue based upon the Millennium Run simulation. The overall properties of groups identified in projection are in general agreement with the best available observational constraints. However, only ∼30 per cent of these simulated groups are found to be truly compact in three dimensions, suggesting that interlopers strongly affect our observed understanding of the properties of galaxies in CGs. These simulations predict that genuine CG galaxies are an extremely homogeneous population, confined nearly exclusively to the red sequence: they are best described as 'red and dead' ellipticals. When interlopers are included, the population becomes much more heterogeneous, due to bluer, star-forming, gas-rich, late-type galaxies incorrectly identified as CG members. These models suggest that selection of members by redshift, such that the line-of-sight velocity dispersion of the group is less than 1000 km s⁻¹, significantly reduces contamination to the 30 per cent level. Selection of members by galaxy colour, a technique used frequently for galaxy clusters, is also predicted to dramatically reduce contamination rates for CG studies.