Sky surveys and deep fields of ground-based and space telescopes

Selected results obtained in major observational sky surveys (DSS, 2MASS, 2dF, SDSS) and deep field observations (HDF, GOODS, HUDF, etc.) are reviewed. Modern surveys provide information on the characteristics and space distribution of millions of galaxies. Deep fields allow one to study galaxies at the stage of formation and to trace their evolution over billions of years. The wealth of observational data is altering the face of modern astronomy: the formulation of problems and their solutions are changing and all the previous knowledge, from planetary studies in the solar system to the most distant galaxies and quasars, is being revised.Comment: 22 pages, 18 figure

Photometric structure of polar-ring galaxies

The results of B, V, R surface photometry of three polar-ring galaxies (PRGs) -- A0017+2212, UGC1198, UGC4385 -- are presented. The data were acquired at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. It was shown that all three galaxies are peculiar late-type spirals in the state of ongoing interaction or merging. We discuss available photometric properties of the PRGs with spiral hosts and consider the Tully-Fisher relation for different types of PRGs. In agreement with Iodice et al. (2003), we have shown that true PRGs demonstrate ~1/3 larger maximum rotation velocities than spiral galaxies of the same luminosity. Peculiar objects with forming polar structures satisfy, on average, the Tully-Fisher relation for disk galaxies but with large scatter.Comment: 12 pages, A&A accepte

Tidal Tails and Galaxy Evolution

We review recent results on the tidal structures of spiral galaxies. Topics included are general characteristics of tails; kinematics of tidal structures and dark haloes of host galaxies; frequency of tidal distortions at z~1.Comment: 5 pages, "Morphology and Dynamics of Stellar Systems: Star Clusters, Galactic Arms and Rings", Proc. JENAM-2000, in pres

Polar-ring galaxies: the SDSS view on the symbiotic galaxies

Polar-ring galaxies are multi-spin systems, showing star formation in a blue late-type component, perpendicular to a red early-type one, revealing how galaxy formation can sometimes occur in successive steps. We perform two-dimensional decomposition in the $g$, $r$, $i$ bandpasses of 50 polar-ring galaxies (PRGs) from the Sloan Digital Sky Survey. Each object was fit with a S\'ersic host galaxy and a S\'ersic ring. Our general results are: (i) The central (host) galaxies of the PRGs are non-dwarf sub-$L^{\ast}$ galaxies with colors typical for early-type galaxies. (ii) Polar structures in our sample are, on average, fainter and bluer than their host galaxies. (iii) In most galaxies, the stellar mass M$_*$ of the polar component is not negligible in comparison with that of the host. (iv) The distributions of the host galaxies on the size -- luminosity and Kormendy diagrams are shifted by $\sim 1^m$ to fainter magnitudes in comparison with E/S0 galaxies. It means that the PRGs hosts are more similar to quenched disks than to ordinary early-type galaxies. (v) All the PRGs in our sample are detected in mid-infrared by WISE, and we derive from the 22$\mu$m luminosity their star formation rate (SFR). Their SFR/M$_*$ ratio is larger than for the early-type galaxy sample of Atlas$^{\rm 3D}$, showing that the star forming disk brings a significant contribution to the new stars. Globally, PRGs appear frequently on the green valley in the mass-color diagram, revealing the symbiotic character between a red-sequence host and a blue cloud ring.Comment: 8 pages, 11 figures, accepted for publication in MNRA

Spiral galaxies with large optical warps

As a result of our statistical study of 540 edge-on galaxies, we present here the images and preliminary statistical analysis of a sub-sample of 60 galaxies, that were selected to be S-type warped spirals. Computing the average volumic density of galaxies from available redshift surveys, a first analysis suggests that warped galaxies are found in denser environments. Only the clearest and strongest warps have been extracted here, and therefore this sample of 60 objects gather the best candidates for future HI or optical works on galaxy warps.Comment: 7 pages, 6 figures, accepted in Astronomy and Astrophysics Su

Statistics of galaxy warps in the HDF North and South

We present a statistical study of the presence of galaxy warps in the Hubble deep fields. Among a complete sample of 45 edge-on galaxies above a diameter of 1.''3, we find 5 galaxies to be certainly warped and 6 galaxies as good candidates. In addition, 4 galaxies reveal a characteristic U-warp. Compared to statistical studies of local warps, and taking into account the strong bias against observing the outer parts of galaxies at high redshift, these numbers point towards a very high frequency of warps at z \sim 1: almost all galaxy discs might be warped. Furthermore, the amplitude of warps are stronger than for local warps. This is easily interpreted in terms of higher galaxy interactions and matter accretion in the past. This result supports these two mechanisms as the best candidates for the origin of early warps. The mean observed axis ratio of our sample of edge-on galaxies is significantly larger in the high-z sample than is found for samples of local spiral galaxies. This might be due to disk thickening due to more frequent galaxy interactions.Comment: 9 pages, 7 figures, accepted in A and

The modified dynamics is conducive to galactic warp formation

There is an effect in the modified dynamics (MOND) that is conducive to formation of warps. Because of the nonlinearity of the theory the internal dynamics of a galaxy is affected by a perturber over and above possible tidal effects. For example, a relatively distant and light companion or the mean influence of a parent cluster, with negligible tidal effects, could still produce a significant warp in the outer part of a galactic disk. We present results of numerical calculations for simplified models that show, for instance, that a satellite with the (baryonic) mass and distance of the Magellanic clouds can distort the axisymmetric field of the Milky Way enough to produce a warp of the magnitude (and position) observed. Details of the warp geometry remain to be explained: we use a static configuration that can produce only warps with a straight line of nodes. In more realistic simulations one must reckon with the motion of the perturbing body, which sometimes occurs on time scales not much longer than the response time of the disk.Comment: Latex, 9 pages, 3 embedded figures, to be published in ApJ

Molecular content of polar-ring galaxies

We have searched for CO lines in a sample of 21 new morphologically determined polar-ring galaxies (of which nine are kinematically confirmed), obtained from a wide search in the Galaxy Zoo project by Moiseev and collaborators. Polar-ring galaxies (PRG) are a unique class of objects, tracing special episodes in the galaxy mass assembly: they can be formed through galaxy interaction and merging, but also through accretion from cosmic filaments. Furthermore, they enable the study of dark matter haloes in three dimensions. The polar ring itself is a sub-system rich in gas, where molecular gas is expected, and new stars are formed. Among the sample of 21 PRG, we have detected five CO-rich systems, that can now be followed up with higher spatial resolution. Their average molecular mass is 9.4 10**9 Mo, and their average gas fraction is 27% of their baryonic mass, with a range from 15 to 43%, implying that they just accreted a large amount of gas. The position of the detected objects in the velocity-magnitude diagram is offset from the Tully-Fisher relation of normal spirals, as was already found for PRGs. This work is part of our multi-wavelength project to determine the detailed morphology and dynamics of polar-ring galaxies, test through numerical models their formation scenario, and deduce their dark matter content and 3D-shape.Comment: 7 pages, 4 figures, accepted in Astronomy and Astrophysic

UGC 7388: a galaxy with two tidal loops

We present the results of spectroscopic and morphological studies of the galaxy UGC7388 with the 8.1-m Gemini North telescope. Judging by its observed characteristics, UGC7388 is a giant late-type spiral galaxy seen almost edge-on. The main body of the galaxy is surrounded by two faint (\mu(B) ~ 24 and \mu(B) ~ 25.5) extended (~20-30 kpc) loop-like structures. A large-scale rotation of the brighter loop about the main galaxy has been detected. We discuss the assumption that the tidal disruption of a relatively massive companion is observed in the case of UGC7388. A detailed study and modeling of the observed structure of this unique galaxy can give important information about the influence of the absorption of massive companions on the galactic disks and about the structure of the dark halo around UGC7388.Comment: 8 pages, 5 figure