Rings are common in disk galaxies. These rings are either indistinguishable from a pair of tightly wound spirals, or themselves are a part of the spiral structure. Furthermore, their occurrence is seen coincident with a bar in the center. In this paper, we interpret this spiral-ring structure as density waves resonantly excited by a rotating bar potential. The theory gives excellent agreement f...

The discovery[1] of a population of young galaxies at an epoch when the universe was about one tenth of its current age has shed new light on the question of when and how galaxies formed. Within the context of popular models[2] this is the population of primeval galaxies that built themselves up to the size of present–day galaxies through the process of repeated mergers. But the recent detectio...

Radio galaxies are uniquely useful as probes of large-scale structure as their uniform identification with giant elliptical galaxies out to high redshift means that the evolution of their bias factor can be predicted. As the initial stage in a project to study large-scale structure with radio galaxies we have performed a small redshift survey, selecting 29 radio galaxies in the range 0.19 < z <...

We present an analysis of the structures, sizes, star formation rates, and local environmental properties of galaxies at z ∼ 4 − 6 (τuniverse < 2 Gyr), utilising deep Hubble Space Telescope imaging of the Hubble Ultra Deep Field. The galaxies we study are selected with the Lyman-break drop-out technique, using galaxies which are B-,V-, and i−drops, which effectively selects UV bright starbursti...

We present an analysis of the structures, sizes, star formation rates and local environmental properties of galaxies at z ∼ 4–6 (τ universe < 2 Gyr), utilizing deep Hubble Space Telescope imaging of the Hubble Ultra Deep Field. The galaxies we study are selected with the Lymanbreak drop-out technique, using galaxies which are B-, Vand i-drops, which effectively selects ultraviolet (UV) bright s...

A complex structure of nuclear disks of normal spiral galaxies is illustrated on the example of five galaxies, observed at 6m telescope. A problem of gravitational stability of nuclear disks is shortly discussed.

We present the first results of an ongoing project to study the morphological, kinematical, dynamical, and chemical properties of satellite galaxies of external giant spiral galaxies. The sample of objects has been selected from the catalogue by Zaritsky et al. (1997). The paper analyzes the morphology and structural parameters of a subsample of 60 such objects. The satellites span a great vari...

The central densities of dark matter (DM) halos are much lower than predicted in cold DM models of structure formation. Confirmation that they have cores with a finite central density would allow us to rule out many popular types of collisionless particle as candidates for DM. Any model that leads to cusped halos (such as cold DM) is already facing serious difficulties on small scales and hot D...

An attempt is made to set constraints on the otherwise ambiguous decomposition of the rotation curves of low surface brightness galaxies into contributions due to the various components of the galaxies. For this purpose galaxies are selected which show clear spiral structure. Arguments of density wave theory of galactic spiral arms are then used to estimate the masses of the galactic disks. The...

The results of a photometric survey of the Fornax dwarf spheroidal galaxy are presented herein. Accurate photometry in two colours (V and I) was collected over a 10 deg area centred on the Fornax system with the aim of searching for extra-tidal structure. The data were complete to a magnitude of V = 20, or approximately one magnitude brighter than the Fornax red clump stars. Stars were selected...