Galactic disks and their evolution

We consider the key problems related to measuring the mass of stellar disks and dark halos in galaxies and to explaining the observed properties of disks formed in massive dark halos.Comment: 6 pages, 2 figure

Mining the Local Volume

After recent systematic optical, IR, and HI surveys, the total number of known galaxies within 10 Mpc has increased from 179 to 550. About half this Local Volume (LV) sample is now been imaged with HST, yielding the galaxy distances with an accuracy of about 8%. For the majority of the LV galaxies we currently have H-alpha fluxes that allow us to reconstruct the star formation history of our neighbourhood. For the late-type LV galaxies their HI masses and angular momentum follow the linear relation in the range of 4 orders, which is expected for rotating gaseous disks being near the gravitational instability threshold. The data obtained on the LV galaxies imply important cosmological parameters, in particular, the mean local matter density and HI mass density, as well as SFR density. Surprisingly, the local Hubble flow around the LV groups is very quiet, with 1D rms deviations of 25 km/s,which is a signature of the Universe vacuum-dominated on small scales. The cold infall pattern around nearby groups provides us with a new method to determine the total mass of the groups independent from virial mass estimates.Comment: 10 pages, 6 figures, proceedings Symposium "Galaxies in the Local Volume", Sydney, 8 - 13 July 2007, B. Koribalski and H. Jerjen, ed

Giant Cyclones in Gaseous Discs of Spiral Galaxies

We report detection of giant cyclonic vortices in the gaseous disc of the spiral galaxy NGC 3631 in the reference frame rotating with the spiral pattern. A presence of such structures was predicted by the authors for galaxies, where the radial gradient of the perturbed velocity exceeds that of the rotational velocity. This situation really takes place in NGC 3631.Comment: 13 pages, 4 EPS and 3 PS figure

Gravitational stability and dynamical overheating of stellar disks of galaxies

We use the marginal stability condition for galactic disks and the stellar velocity dispersion data published by different authors to place upper limits on the disk local surface density at two radial scalelengths $R=2h$. Extrapolating these estimates, we constrain the total mass of the disks and compare these estimates to those based on the photometry and color of stellar populations. The comparison reveals that the stellar disks of most of spiral galaxies in our sample cannot be substantially overheated and are therefore unlikely to have experienced a significant merging event in their history. The same conclusion applies to some, but not all of the S0 galaxies we consider. However, a substantial part of the early type galaxies do show the stellar velocity dispersion well in excess of the gravitational stability threshold suggesting a major merger event in the past. We find dynamically overheated disks among both seemingly isolated galaxies and those forming pairs. The ratio of the marginal stability disk mass estimate to the total galaxy mass within four radial scalelengths remains within a range of 0.4---0.8. We see no evidence for a noticeable running of this ratio with either the morphological type or color index.Comment: 25 pages, 5 figures, accepted to Astronomy Letter

New Structures in Galactic Disks: Predictions and Discoveries

Original paper can be found at http://www.astrosociety.org/pubs/cs/222-252.html--Copyright Astronomical Society of the Pacific --Our main goal is to review: 1) some physical mechanisms which form the observed structures in galactic disks; 2) the discovery of new galactic structures predicted earlier. Specifically in the first part of the paper we discuss some questions associated with spiral structure. The second part is devoted to the prediction and discovery of giant vortices in gaseous disks of the grand design spiral galaxies using method of reconstruction of the full three-component velocity field from the observed line-of-sight velocity field. In the third part, we give some arguments in favour of existence of the slow bars in the grand design spiral galaxies

Polygonal Structures in the Gaseous Disk: Numerical Simulations

The results of numerical simulations of a gaseous disk in the potential of a stellar spiral density wave are presented. The conditions under which straightened spiral arm segments (rows) form in the gas component are studied. These features of the spiral structure were identified in a series of works by A.D. Chernin with coauthors. Gas-dynamic simulations have been performed for a wide range of model parameters: the pitch angle of the spiral pattern, the amplitude of the stellar spiral density wave, the disk rotation speed, and the temperature of the gas component. The results of 2D- and 3D-disk simulations are compared. The rows in the numerical simulations are shown to be an essentially nonstationary phenomenon. A statistical analysis of the distribution of geometric parameters for spiral patterns with rows in the observed galaxies and the constructed hydrodynamic models shows good agreement. In particular, the numerical simulations and observations of galaxies give $\simeq 120^\circ$ for the average angles between straight segments.Comment: 22 pages, 10 figure

Tides in colliding galaxies

Long tails and streams of stars are the most noticeable upshots of galaxy collisions. Their origin as gravitational, tidal, disturbances has however been recognized only less than fifty years ago and more than ten years after their first observations. This Review describes how the idea of galactic tides emerged, in particular thanks to the advances in numerical simulations, from the first ones that included tens of particles to the most sophisticated ones with tens of millions of them and state-of-the-art hydrodynamical prescriptions. Theoretical aspects pertaining to the formation of tidal tails are then presented. The third part of the review turns to observations and underlines the need for collecting deep multi-wavelength data to tackle the variety of physical processes exhibited by collisional debris. Tidal tails are not just stellar structures, but turn out to contain all the components usually found in galactic disks, in particular atomic / molecular gas and dust. They host star-forming complexes and are able to form star-clusters or even second-generation dwarf galaxies. The final part of the review discusses what tidal tails can tell us (or not) about the structure and content of present-day galaxies, including their dark components, and explains how tidal tails may be used to probe the past evolution of galaxies and their mass assembly history. On-going deep wide-field surveys disclose many new low-surface brightness structures in the nearby Universe, offering great opportunities for attempting galactic archeology with tidal tails.Comment: 46 pages, 13 figures, Review to be published in "Tidal effects in Astronomy and Astrophysics", Lecture Notes in Physics. Comments are most welcom

Gas motions in the plane of the spiral galaxy NGC 3631

Peer reviewe

Vertical motions in the gaseous disk of the spiral galaxy NGC 3631

Full text of this article is not available in the UHRA.Peer reviewe