Galaxies in the First Billion Years After the Big Bang

Наша Вселенная существует и расширяется уже 13.8 млрд лет. Первые галактики внутри нее — гигантские звездно-газовые системы — тоже появились давно, более 13 млрд лет назад. Какими они были на заре эволюции Вселенной, в первый миллиард лет после Большого взрыва? Космологическая теория давно нарисовала полную картину. Но кое-что мы уже узнали и из наблюдений, и далеко не все обнаруженное похоже на предсказанное теоретиками...Our Universe exists and expands for 13.8 Gyr. And the first galaxies — giand stellar-gaseous systems — have also formed more than 13 Gyr ago. What did they look like in the first Gyr after the Big Bang? The cosmologists think that they know exactly. But the observations have already provided some information on this subject, and it contradicts the theory in some important points..

Evolution of Galaxies

I would talk about evolution of galaxies as we can only imagine it currently. The evolution of galaxies can be studied through two different approach: we can study in detail some nearby galaxies of various morphological types and try to construct models with the similar final properties; or we can observe distant galaxies at various redshifts which, due to the finite light speed, represent different evolutionary stages, starting from the earliest ones. The most important processes in the life of a galaxy are: dynamical evolution which shapes also its structure; evolution of the stellar population which is simultaneously spectrophotometric evolution; and the chemical evolution which drives the metallicity growth in the gas and stars of the galaxy. The main contributor into many of these evolutionary processes is star formation history of a galaxy.В лекции будет рассказано об эволюции галактик, как мы ее сейчас себе представляем. Эволюция галактик может изучаться с помощью двух основных подходов либо подробное исследование близких галактик разных типов и построение моделей, которые дают похожие на наблюдаемые конечные результаты эволюции; либо прямое наблюдение галактик на разных красных смещениях, что из-за конечной скорости света позволяет увидеть последовательные стадии эволюции, начиная с самых ранних. В жизни галактики важны следующие процессы, составляющие разные стороны ее эволюции: динамическая эволюция, определяющая также и структуру галактики; эволюция звездного населения, определяющая интегральное излучение галактики; наконец, химическая эволюция, отражающая изменение химического состава газа и звезд в галактике. Одним из самых главных вкладчиков в эти различные стороны эволюции галактики является ее история звездообразования

Star Formation in Galaxies: a Cosmological Context

I would talk about star formation in galaxies which is the main driver of their evolution. The principal concept is: stars are formed from gas, in dense molecular clouds. Then the main factor determining the currect star formation rate is amount of gas. But observationally the star formation rate depends also on potential well depth, on angular momentum, on triggering by spiral density waves and by nearby supernova remnants, on outer gas accretion... It is so quite clear that the cosmic star formation history is rather complex.В лекции будет рассказано о звездообразовании в галактиках, которое во многом определяет ход их эволюции. Основная концепция звездообразования: звезды образуются из газа в плотных молекулярных облаках. Соответственно главное, от чего зависит мгновенный темп звездообразования, — количество газа. Но темп звездообразования еще зависит и от глубины ямы гравитационного потенциала, и от момента вращения, и от стимулирующего влияния спиральных волн плотности и соседних остатков сверхновых, и от аккреции газа извне. Неудивительно, что космическая история звездообразования при этом имеет далеко не простой ход

Galaxies as open systems

Эволюция галактик подразумевает изменения ее основных характеристик: размеров, структуры, химического состава звезд, полной звездной массы... И в большинстве галактик эти изменения довольно плавные. Что управляет эволюцией галактик? Есть ли один главный физический фактор, от которого зависит все? В последние годы астрономы склоняются к мысли, что есть: это постоянный приток холодного газа извне, геометрия и темпы которого определяют практически все особенности состояния каждой отдельной галактики в разные эпохи. А вот отождествить источник этого внешнего газа - пока нерешенная и крайне актуальная проблема.The galaxy evolution implies permanent change of its main parameters: size, structure, chemical composition of stars, the total stellar mass... Many galaxies proceed their evolution very smoothly. What governs the evolution of galaxies? If does a single physical factor exist which determines all these characteristics? Currently astronomers think that it exists. It is a steady outer cold gas inflow, and its rate and geometry define completely the evolutionary state of a galaxy in every moment of its evolution. To find a source of this outer cold gas is a quite actual problem, unsolved yet

Ionized and neutral gas in the peculiar star/cluster complex in NGC 6946

The characteristics of ionized and HI gas in the peculiar star/cluster complex in NGC 6946, obtained with the 6-m telescope (BTA) SAO RAS, the Gemini North telescope, and the Westerbork Synthesis Radio Telescope (WSRT), are presented. The complex is unusual as hosting a super star cluster, the most massive known in an apparently non-interacting giant galaxy. It contains a number of smaller clusters and is bordered by a sharp C-shaped rim. We found that the complex is additionally unusual in having peculiar gas kinematics. The velocity field of the ionized gas reveals a deep oval minimum, ~300 pc in size, centered 7" east of the supercluster. The Vr of the ionized gas in the dip center is 100 km/s lower than in its surroundings, and emission lines within the dip appear to be shock excited. This dip is near the center of an HI hole and a semi-ring of HII regions. The HI (and less certainly, HII) velocity fields reveal expansion, with the velocity reaching ~30 km/s at a distance about 300 pc from the center of expansion, which is near the deep minimum position. The super star cluster is at the western rim of the minimum. The sharp western rim of the whole complex is plausibly a manifestation of a regular dust arc along the complex edge. Different hypotheses about the complex and the Vr depression origins are discussed, including a HVC/dark mini-halo impact, a BCD galaxy merging, and a gas outflow due to release of energy from the supercluster stars.Comment: MN RAS, accepte

A new method for reconstructing the density distribution of matter in the disks of spiral galaxies from the rotation velocity curve in it

In this paper we propose a new method for reconstructing the surface density of matter in flat disks of spiral galaxies. The surface density is expressed through observational rotation velocity curves of visible matter in the disks of spiral galaxies. The new method is not based on quadrature of special functions. The found solution is used for processing and analysis of observational data from several spiral galaxies. The new method can be used to more accurately estimate the amount of dark matter in spiral galaxies.Comment: 18 pages, 6 figure

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

Multifractal characterization of stochastic resonance

We use a multifractal formalism to study the effect of stochastic resonance in a noisy bistable system driven by various input signals. To characterize the response of a stochastic bistable system we introduce a new measure based on the calculation of a singularity spectrum for a return time sequence. We use wavelet transform modulus maxima method for the singularity spectrum computations. It is shown that the degree of multifractality defined as a width of singularity spectrum can be successfully used as a measure of complexity both in the case of periodic and aperiodic (stochastic or chaotic) input signals. We show that in the case of periodic driving force singularity spectrum can change its structure qualitatively becoming monofractal in the regime of stochastic synchronization. This fact allows us to consider the degree of multifractality as a new measure of stochastic synchronization also. Moreover, our calculations have shown that the effect of stochastic resonance can be catched by this measure even from a very short return time sequence. We use also the proposed approach to characterize the noise-enhanced dynamics of a coupled stochastic neurons model.Comment: 10 pages, 21 EPS-figures, RevTe