Lensing clusters of galaxies in the SDSS-Ⅲ

We identify new strong lensing clusters of galaxies from the Sloan Digital Sky Survey III (SDSS DR8) by visually inspecting color images of a large sample of clusters of galaxies. We find 68 new clusters showing giant arcs in addition to 30 known lensing systems. Among 68 cases, 13 clusters are almost certain lensing systems with tangential giant arcs, 22 clusters are probable and 31 clusters are possible lensing systems. We also find two exotic systems with blue rings. The giant arcs have angular separatio...     

Evolution effects in the distribution of distant galaxies?

The amplitudes of the two-point correlation function for galaxies are compared for galaxy catalogues extending to different depths. Strong evolution effects in the pattern of galaxy distribution seem to be present suggesting a secular increase of the clustering amplitude. Other explanations would involve large errors in the identification of faint objects as galaxies or a considerable contamination of the counts by very young highly redshifted galaxies as recently proposed by TINSLEY .     

Weak redshift discretisation in the Local Group of galaxies?

We discuss the distribution of radial velocities of galaxies belonging to the Local Group. Two independent samples of galaxies as well as several methods of reduction from the heliocentric to the galactocentric radial velocities are explored. We applied the power spectrum analysis using the Hann function as a weighting method, together with the jackknife error estimation. We performed a detailed analysis of this approach. The distribution of galaxy redshifts seems to be non‐random. An excess of galaxies with radial velocities of ∼24 km s^–1 and ∼36 km s^–1 is detected, but the effect is statistically weak. Only one peak for radial velocities of ∼24 km s^–1 seems to be confirmed at the confidence level of 95%. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The influence of magnetic fields on the Sunyaev–Zel’dovich effect in clusters of galaxies

We study the influence of intracluster large scale magnetic fields on the thermal Sunyaev–Zel’dovich (SZ) effect. In a macroscopic approach we complete the hydrostatic equilibrium equation with the magnetic field pressure component. Comparing the resulting mass distribution with a standard one, we derive a new electron density profile. For a spherically symmetric cluster model, this new profile can be written as the product of a standard (β-) profile and a radius dependent function, close to unity, which takes into account the magnetic field strength. For non-cooling flow clusters we find that the observed magnetic field values can reduce the SZ signal by ∼10% with respect to the value estimated from X-ray observations and the β-model. If a cluster harbours a cooling flow, magnetic fields tend to weaken the cooling flow influence on the SZ-effect.     

Radio-continuum study of the Nearby sculptor group galaxies. Part 1: NGC 300 at λ=20 cm

A series of new radio-continuum (λ=20 cm) mosaic images focused on the NGC?300 galactic system were produced using archived observational data from the VLA and/or ATCA. These new images are both very sensitive (rms?=60 μJy) and feature high angular resolution (<10?″). The most prominent new feature is the galaxy’s extended radio-continuum emission, which does not match its optical appearance. Using these newly created images a number of previously unidentified discrete sources have been discovered. Furthermore, we demonstrate that a joint deconvolution approach to imaging this complete data-set is inferior when compared to an immerge approach.     

On the formation of superdense gaseous cores in the nuclei of disk galaxies — I

A model for the formation of superdense gaseous cores by accretion in the nuclei of disk galaxies has been proposed. Equations for radial flow of gas into the nucleus in the presence of aweak galactic magnetic field have been solved, and time scales for the accretion of an exploding mass in the nucleus (10⁹ M ) have been obtained under several different situations in the absence of any rotation. The time scales are found to lie in the range between a few times 10⁷ yr and 10⁸ yr. Such time scales have been proposed by some authors for repeated explosions in the nuclei of galaxies; they have also proposed that spiral arms in disk galaxies are repeatedly formed and destroyed over such time scales. It is shown that the presence of rotational velocities in the infalling gas practically destroys the efficiency of the accretion process unless such velocities are dissipated by frictional forces within the system. Viscosity of gas is the most obvious dissipative agent. The problem of accretion of a rotating viscous gas will be discussed in a subsequent paper.     

Are ring galaxies the ancestors of giant low surface brightness galaxies?

We simulate the collisional formation of a ring galaxy and we integrate its evolution up to 1.5 Gyr after the interaction. About 100–200 Myr after the collision, the simulated galaxy is very similar to observed ring galaxies (e.g. Cartwheel). After this stage, the ring keeps expanding and fades. Approximately 0.5–1 Gyr after the interaction, the disc becomes very large (∼100 kpc) and flat. Such extended discs have been observed only in giant low surface brightness galaxies (GLSBs). We compare various properties of our simulated galaxies (surface brightness profile, morphology, H  i spectrum and rotation curve) with the observations of four well-known GLSBs (UGC 6614, Malin 1, Malin 2 and NGC 7589). The simulations match quite well the observations, suggesting that ring galaxies could be the progenitors of GLSBs. This result is crucial for the cold dark matter (CDM) model, as it was very difficult, so far, to explain the formation of GLSBs within the CDM scenario.     

Characteristic actionsħ (s) in the structure of the universe and the problem of the origin of galaxies

From the characteristic actions ^(s), we can derive various relations between the basic characteristic quantities of objects and the fundamental constants in known physical laws. The main physical processes which lead to the formation of objects should be included in some such reletions through the fundamental constants. The problem of the origin of galaxies has been considered on the basis of the theory of actions ^(s). It has been shown that in addition to gravitational effect, the dissipation process of the adiabatic density perturbations arising from the Thomson scattering in the early universe is a crucial process in forming galaxies; and if the Hubble constant has a valueH ₀ 50 km s^–1 Mpc^–1, the protogalaxies might be formed just before recombination.     

Tidal structures of z ∼ 1 galaxies in the Hubble Deep Field

An analysis of the images of objects in the Northern Hubble Space Telescope Deep Field has revealed twelve galaxies with tidal tails at redshifts from 0.5 to 1.5. The integrated characteristics of the newly discovered tidal structures are found to be similar to those of the tails of local interacting galaxies. The space density of galaxies with tidal tails is found to depend on z as (1+z)^4±1(q ₀=0.05), according to the data on objects with z=0.5–1.0. The exponent decreases to 3.6 if barred galaxies are included. The change in the rate of close encounters between galaxies of comparable masses (i.e., those that produce extended tidal structures) is estimated. If the rate of galactic mergers is governed by the same process, our data are indicative of the rapid evolution of galaxy merger rate toward z ～ 1.     

Interactions and star-formation activity in Wolf–Rayet galaxies

We present the main results of the Ph.D. thesis carried out by López-Sánchez (Ph.D. thesis, 2006), in which a detailed morphological, photometric and spectroscopic analysis of a sample of 20 Wolf–Rayet (WR) galaxies was performed. The main aims are the study of the star formation and O and WR stellar populations in these galaxies, and the role that interactions between low surface brightness companion objects have in the triggering of the bursts. We analyze the morphology, stellar populations, physical conditions, chemical abundances and kinematics of the ionized gas, as well as the star-formation activity of each system.     

Estimates of the number of sunspot groups: Application to the activity cycle 1960–1970

It was verified that the total number of sunspot groups at certain region on the solar surface for a certain activity cycle can be estimated quite accurately by using the Markov chain approximation method on the total number of spot groups observed on the same region at an earlier activity cycle. Application has been carried out on the observed sunspots on three northern longitude intervals (40–50, 80–90, and 130–140) during the activity cycle 1950–1960 and 1960–1970. The total number of spot groups in these regions for the activity cycle 1960–1970 has been estimated from the observational data of the cycle 1950–1960. A good correlation between the observed and estimated number of spot groups for the activity cycle 1960–1970 has been noted.     

Prospects of the “WSO-UV” Project for Star Formation Study in Nearby Dwarf Galaxies

In the present work we consider the questions of star formation and evolution of nearby dwarf galaxies. We describe the method of star formation history determination based on multicolor photometry of resolved stars and models of color-magnitude diagrams of the galaxies. We present the results of star formation rate determination and its dependence on age and metallicity for dwarf irregular and dwarf spheroidal galaxies in the two nearby galaxy groups M81 and Cen A. Similar age of the last episode of star formation in the central part of the M81 group and also unusually high level of metal enrichment in the several galaxies of the Cen A group are mentioned. We pay special attention to the consideration of perspectives of star formation study in nearby dwarf galaxies with he new WSO-UV observatory.     

Morphology and structure of BzK-selected galaxies at z ～ 2 in the CANDELS-COSMOS field

Utilizing a Bz K-selection technique, we obtain 14 550 star-forming galaxies(sB z Ks) and 1763 passive galaxies(p Bz Ks) at z ～ 2 from the K-selected(KAB 22.5) catalog in the COSMOS/Ultra VISTA field. The differential number counts of sB z Ks and p Bz Ks are consistent with the results from the literature.Compared to the observed results, semi-analytic models of galaxy formation and evolution provide too few(many) galaxies at the high(low) mass end. Moreover, we find that the star formation rate and stellar mass of sB z Ks follow the relation of the main sequence. Based on HST/Wide Field Camera 3 F160 W imaging, we find a wide range of morphological diversities for sB z Ks, from diffuse to early-type spiral structures, with relatively high M20, large size and low G, while p Bz Ks have elliptical-like compact morphologies with lower M20, smaller size and higher G, indicating a more concentrated and symmetric spatial extent of stellar population distribution in p Bz Ks than sB z Ks. Furthermore, the sizes of p Bz Ks(sB z Ks) at z ～ 2 are on average two to three(one to two) times smaller than those of local early-type(late-type) galaxies with similar stellar mass. Our findings imply that the two classes have different evolution models and mass assembly histories.     

Spectral energy distribution similarity of the local galaxies and the 3.6 μm selected galaxies from the Spitzer Extended Deep Survey

The Spitzer Extended Deep Survey(SEDS)as a deep and wide mid-infrared(MIR)survey project provides a sample of 500 000+sources spreading 1.46 square degree and a...     

Substructure in clusters of galaxies: A clue to the ‘missing’ mass?

The influence of subclustering in rich clusters of galaxies is examined using results from numericaln-body experiments. It is found that, under some conditions, the standard virial theorem is satisfied. No physical missing mass is needed because its role is replaced by the gravitational energy of the subclustering. We find that, in the Coma cluster, this effect masquerades as a missing mass about 7 times that of the physical mass, so that the apparent extant virial discrepancy (M _VT/M8) in this cluster is explained.     

〔C II〕Continuum Intensity Ratio in the Far-Infrared Toward the Central Kiloparsec of the Nearby Spiral Galaxy M31

1　ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅ〔ＣＩＩ〕1 5 8μｍ ( 2 Ｐ3 /2 →2 Ｐ1/2 )ｅｍｉｓｓｉｏｎｌｉｎｅｏｆｔｅｎｄｏｍｉｎａｔｅｓｔｈｅｇａｓｃｏｏｌｉｎｇｉｎｔｈｅｎｅｕ ｔｒａｌｐｈａｓｅｏｆｔｈｅｇａｌａｃｔｉｃＩＳＭ (ｉｎｔｅｒｓｔｅｌｌａｒｍｅｄｉｕｍ) .ＴｈｉｓｌｉｎｅｉｓｗｅｌｌｃｏｒｒｅｌａｔｅｄｏｎａｇａｌａｃｔｉｃｓｃａｌｅｗｉｔｈＦＩＲ (ｆａｒ-ｉｎｆｒａｒｅｄ)ｃｏｎｔｉｎｕｕｍ ,ｗｈｉｃｈｔｒａｃｅｓｔｈｅｃｏｏｌｉｎｇｏｆｄｕｓｔｇｒａｉｎｓ.Ｎｅａｒｌｙｃｏｎｓｔａｎｔｉｎ…     

Ambartsumian’s paradigm for the activity of galactic nuclei and the evolution of galaxies

Ambartsumian’s paradigm for the creation of galaxies owing to the decay of denser matter is examined. The roots of this concept can be found in the very earliest papers of Ambartsumian on quantum fields and the structure of atomic nuclei. In the early 1930’s his papers contained new ideas regarding the ejection by one physical object of another which had not originally existed inside the first. The basic observational data which served as the basis for the final formulation of the new concept are described. Special attention is devoted to those objects and phenomena, which, upon further study, have confirmed the validity of Ambartsumian’s reasoning and arguments. It is noted that the discovery of Hubble expansion’s acceleration of the universe opened up new possibilities for the interpretation of activity phenomena in terms of Ambartsumian’s concept. The further extension of this concept is discussed and it is suggested that the major result of this approach should be the proof of the existence of galaxies of all ages within a finite volume of space.     

Dependence of Fanaroff–Riley break of radio galaxies on luminosity and redshift

We investigate the dependence of the Fanaroff–Riley (FR) 1/2 dichotomy of radio galaxies on their luminosities and redshifts. Because of a very strong redshift-luminosity correlation (Malmquist bias) in a flux-limited sample, any redshift-dependent effect could appear as a luminosity-related effect and vice versa. A question could then arise—do all the morphological differences seen in the two classes (FR 1 and 2 types) of sources, usually attributed to the differences in their luminosities, could as well be primarily a redshift-dependent effect? A sharp break in luminosity, seen among the two classes, could after all reflect a sharp redshift dependence due to a rather critical ambient density value at some cosmic epoch. A doubt on these lines does not seem to have been raised in past and things have never been examined with this particular aspect in mind. We want to ascertain the customary prevalent view in the literature that the systematic differences in the two broad morphology types of FR 1 and 2 radio galaxies are indeed due to the differences in their luminosities, and not due to a change in redshift. Here we investigate the dependence of FR 1/2 dichotomy of radio galaxies on luminosity and redshift by using the 3CR sample, where the FR 1/2 dichotomy was first seen, supplemented by data from an additional sample (MRC), that goes about a factor of 5 or more deeper in flux-density than the original 3CR sample. This lets us compare sources with similar luminosities but at different redshifts as well as examine sources at similar redshifts but with different luminosities, thereby allowing us a successful separation of the otherwise two intricately entangled effects. We find that the morphology type is not directly related to redshift and the break between the two types of morphologies seems to depend only upon the radio luminosity.     

Identification of lines in the spectrum of the quasar 0237–233

The emission and absorption lines (3716–4290) in the spectrum of the quasar 0237–233 are identified within the framework of the PLS model. The available evidence indicates that it is a helium star. Similarities between the spectral properties of 0237–233 and the star Upsilon Sagittarii are pointed out. Predictions are made for the absorption-line spectrum which falls outside 3716–4290 and also for an expected discontinuity at 2600.     

What can we learn from arcs in clusters of galaxies?

Photon-counting techniques have been applied to a study of the movement of the image of an unresolved star at the 50 cm telescope of the Royal Academy of Sciences, at the Roque de los Muchachos Observatory. The temporal autocorrelation function of such movement has been computed, the results are discussed in terms of atmospheric turbulence and in relation to high-resolution imaging.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.