Color redshifts and the age of the stellar population of distant RC radio galaxies

BV RI data are presented for the majority of steep-spectrum objects in the RC catalog with m _R <23.5^m. Previously developed programs are applied to these data to estimate the redshifts and ages of the stellar systems of the host galaxies. Applying this program to the color data (BV RI JHK) for distant radio galaxies with spectroscopic redshifts indicates that this approach provides accurate estimates of the redshifts of such radio galaxies, close to those obtained using field galaxies (～20%). The age estimates are much less trustworthy, but a lower limit to the ages of objects that are not very distant (z<1.5) can be determined with certainty. We have identi fied several galaxies whose formal ages exceed the age of the Universe at the corresponding z in simple Cold Dark Matter models for the Universe. The possibility of using such objects to elucidate the role of “dark energy” is discussed. This paradox disappears in models with cosmological constants (Λ terms) equal to 0.6–0.8.     

The radio sources CTA 21 and OF+247: The hot spots of radio galaxies

The physical conditions in the radio sources CTA 21 and OF+247 are studied assuming that the low-frequency spectral turnovers are due to synchrotron self-absorption. The physical parameters of the radio sources are estimated using a technique based on a nonuniform synchrotron source model. It is shown that the magnetic-field distributions in the dominant compact components of these radio sources are strongly inhomogeneous. The magnetic fields at the center of the sources are B ～ 10^?1 G, and the fields are two to three orders of magnitude weaker at the periphery. The magnetic field averaged over the compact component is B ～ 10^?3 G, and the density of relativistic electrons is n _e ～ 10^?3 cm^?3. Assuming that there is equipartition of the energies of the magnetic field and relativistic particles, averaged over the source, 〈E _H 〉 = 〈E _e 〉 ～ 10^?7–10^?6 erg cm^?3. The energy density of the magnetic field exceeds that of the relativistic electrons at the centers of the radio sources. The derived parameters of CTA 21 and OF+247 are close to those of the hot spots in the radio galaxy Cygnus A. On this basis, it is suggested that CTA 21 and OF+247 are radio galaxies at an early stage of their evolution, when the hot spots (dominant compact radio components) have appeared, and the radio lobes (weak extended components) are still being formed.     

The nature of active radio galaxies in the cluster A569

We investigate the nature of bright radio sources with known radio spectra in the direction of the nearby cluster of galaxies A569 (z=0.0193). The optical identifications of the sources show that 45% of these radio sources are associated with compact galaxies. A substantial fraction of these galaxies have active nuclei, with the radio emission concentrated toward the galactic center. Some of the cluster galaxies have radio halos, with appreciably weaker radio powers and spectral indices α=0.95±0.2. We compute the magnetic fields in the nuclei and halos of the galaxies for the adopted distance to A569. As expected, the magnetic fields in the galactic halos make a smooth transition to the intergalactic field, while the magnetic fields in the central regions of the galaxies rise sharply toward the nucleus.     

The search for giant radio galaxies in the PS 102 survey

The possibility of selecting extended radio sources that are potential candidates for giant radio galaxies among objects in the Pushchino catalog at 102 MHz is considered. The method used is based on the analysis of objects in a α ₁–α ₂ diagram, where α ₁ and α ₂ are two-frequency spectral indices (S _ν ～ ν ^?α ), formally calculated using 102–365 and 365–1400 MHz data, based on the identifications of Pushchino radio sources with objects of the Texas (365 MHz) and Green Bank (1400 MHz) catalogs. The calculated spectra are abnormally steep at 102–365 MHz and flat or even inverted at 365–1400 MHz, due to the fact that the 365-MHz flux densities of extended radio sources measured with the Texas radio interferometer are appreciably underestimated. Ten objects among the fifteen Pushchino radio sources selected using this criterion proved to be already known large radio galaxies. The possibility of improving the efficiency of the method by using larger samples and applying some additional criteria selecting candidate giant radio galaxies is considered.     

Radio spectra of giant radio galaxies from RATAN-600 data

Measurements of the flux densities of the extended components of seven giant radio galaxies obtained using the RATAN-600 radio telescope at wavelengths of 6.25 and 13 cm are presented. The spectra of components of these radio galaxies are constructed using these new RATAN-600 data together with data from the WENSS, NVSS, and GB6 surveys. The spectral indices in the studied frequency range are calculated, and the need for detailed estimates of the integrated contribution of such objects to the background emission is demonstrated.     

A second set of RATAN-600 observations of giant radio galaxies

Results of RATAN-600 centimeter-wavelength flux-density measurements of the extended components in five giant radio galaxies are reported. The spectra of the components of these radio galaxies have been constructed using the data of the WENSS, NVSS, and GB6 surveys together with new RATAN-600 data. Spectral indices in the studied frequency range have been calculated.     

Phenomenological model for the evolution of radio galaxies such as Cygnus A

A phenomenological model for the evolution of classical radio galaxies such as Cygnus A is presented. An activity cycle of the host galaxy in the radio begins with the birth of radio jets, which correspond to shocks on scales ～1 pc (the radio galaxy B0108+388). In the following stage of the evolution, the radio emission comes predominantly from formations on scales of 10–100 pc, whose physical parameters are close to those of the hot spots of Cygnus A (this corresponds to GHz-peaked spectrum radio sources). Further, the hot spots create radio lobes on scales of 10³–10⁴ pc (compact steep-spectrum radio sources). The fully formed radio galaxies have radio jets, hot spots, and giant radio lobes; the direction of the jets can vary in a discrete steps with time, creating new hot spots and inflating the radio lobes (as in Cygnus A). In the final stage of the evolutionary cycle, first the radio jets disappear, then the hot spots, and finally the radio lobes (similar to the giant radio galaxies DA 240 and 3C 236). A large fraction of radio galaxies with repeating activity cycles is observed. The close connection between Cygnus A-type radio galaxies and optical quasars is noted, as well as similarity in the cosmological evolution of powerful radio galaxies and optical quasars.     

Estimating the masses of the spherical and disk components of galaxies via numerical simulations

A series of numerical N-body simulations is performed in order to dynamically model the properties of four galaxies (NGC 5603, NGC 3198, NGC 891, and NGC 1566) with known rotation curves, radial disk scales L, and velocity dispersions of old disk stars at various galactocentric distances r. Each model includes a three-dimensional collisionless disk and rigid spherical components, whose relative mass μ was treated as a free parameter that differed from simulation to simulation. The observed disk stellar velocity dispersions were assumed to be equal to or (in the general case) greater than the corresponding line-of-sight projections of the simulated values for the adopted μ after the initially unstable disk is heated and arrives at a steady state. A comparison of the simulated and observed rotational velocities and velocity dispersions provides evidence for “light” disks with μ≥2 in the disk (r<4L).     

Kinematics of disk galaxies with known masses of their supermassive black holes. Observations

This is the first paper in a project aimed at analyzing relations between the masses of supermassive black holes or nuclear clusters in galaxies and the kinematic features of the host galaxies. We present long-slit spectroscopic observations of galaxies obtained on the 6-m telescope of the Special Astrophysical Observatory using the SCORPIO focal reducer. Radial profiles of the line-of-sight velocities and velocity dispersions of the stellar populations were obtained for seven galaxies with known masses of their supermassive black holes (Mkn 79, Mkn 279, NGC 2787, NGC 3245, NGC 3516, NGC 7457, and NGC 7469), and also for one galaxy with a nuclear cluster (NGC 428). Velocity profiles of the emitting gas were obtained for some of these galaxies as well. We present preliminary galactic rotation curves derived from these data.     

The stellar structure of irregular galaxies. Face-on galaxies

Stellar photometry of nearby irregular galaxies of the Local Group is used to identify and study the young and old stellar populations of these galaxies. An analysis of the spatial distributions of stars of different ages in face-on galaxies shows that the young stellar populations in irregular galaxies are concentrated toward the center, and form local inhomogeneities in star-forming regions, while the old stellar populations—red giants—form extended structures around the irregular galaxies. The sizes of these structures exceed the visible sizes of the galaxies at the 25^m/arcsec² isophote by a factor of two to three. The surface density of the red giants decreases exponentially from the center toward the edge, similar to the disk components in spiral galaxies.     

A possible relation between the masses of black holes in galactic nuclei and the parameters of the host galaxies

Data on about forty virialized galaxy clusters with bright central galaxies, for which both the galactic velocity dispersion (?? _gal) and the stellar velocity dispersion in the brightest galaxies (??*) are measured, have been used to obtain several approximate relations between ?? _gal, ??*, the absolute B magnitude of the brightest central galaxyM _B ^BCG , and the mass of the central massive black holeM _BH: $\begin{gathered} \log \sigma _* = (0.12 \pm 0.14)\log \sigma _{gal} + (2.1 \pm 0.4), \hfill \\ \log \sigma _* = - (0.15 \pm 0.02)M_B^{BCG} + (0.85 \pm 0.5), \hfill \\ \log M_{BH} = 0.51\log \sigma _{gal} + 7.28. \hfill \\ \end{gathered} $ . These relations can be used to derive crude estimates ofMBH in the nuclei of the brightest galaxies using the parameters of the both host galaxies and the host galaxy clusters. The last relation above confirms earlier suggestions of a quadratic relation between the masses of the coronas of the host systems and the masses their central objects: M _hg ^halo ?? M _cent ² . The relations obtained are consistent with the common evolution of subsystems with different scales and masses formed in the process of hierarchical clustering.     

The angular-momentum distribution in axisymmetrical galaxies

We investigate the angular-momentum distribution in a classical homogeneous Maclaurin spheroid. An exact formula for the distribution as a function of the mass of a cylindrical column in the spheroid is obtained in both integral and differential forms. This expression is used to calculate the angular-velocity distributions in galaxies evolving from initially spheroidal configurations to steady-state configurations with observed density distributions.     

Study of the physical conditions in active galactic nuclei. Physical conditions in the cores of two nearby radio galaxies

We have carried out a search for compact radio sources in the cores of 16 nearby radio galaxies. We detected compact components in four radio galaxies, and found upper limits for the flux density in compact components in ten radio galaxies. VLBI observations enabled the detection of a turnover in the spectra of the two nearby radio galaxies 3C 111 and 3C 465. Using a method based on an inhomogeneous model for a synchrotron source, we estimate the magnetic-field strength and the energy densities in the magnetic field and relativistic electrons in the cores of these radio galaxies. Strong inhomogeneity in the distribution of the magnetic fields in the cores of 3C 111 and 3C 465 is implied by our analysis. The magnetic-field strengths in the central regions of these galactic nuclei, on scales of ～0.1 pc, exceed the mean strength by four to five orders of magnitude, and lie in the range 10² G < H < 10⁴ G.     

Atomic hydrogen deficiency in galaxies of the virgo and coma clusters: A new estimation method

We propose a new method for estimating the HI deficiency in galaxies. The method is based on a semi-empirical relationship between the total mass of HI and specific angular momentum of isolated galaxies. The atomic-hydrogen deficiency is estimated for nearby spiral galaxies and for spiral galaxies in the Virgo and Coma clusters. The mean HI deficiencies determined for these samples using our method are similar to those obtained with conventional methods, although there are considerable differences in some cases. The HI deficiency in nearby galaxies does not depend on their degree of isolation, and there is no systematic discrepancy between their HI and “normal” masses. Significant HI deficiencies are observed in the Virgo and Coma clusters, out to distances of 1.5 and 3–4 Mpc from the cluster centers, respectively. At such distances, the ram pressure is too small to sweep a considerable amount of gas from the galactic disks. Either these galaxies have passed through the dense cluster center, or their gas deficiency is due to the fact that the halo had stopped accreting onto the disk when the galaxy entered the cluster.     

The minimum stellar mass in early galaxies

The conditions for the fragmentation of the baryonic component during mergers of dark matter halos in the early Universe are studied. We assume that the baryonic component undergoes a shock compression. The characteristic masses of protostellar molecular clouds and the minimum masses of protostars originating in these clouds decrease with increasing halo mass. This may indicate that the initial stellar mass function in more massive galaxies was shifted towards lower masses during the initial stages of their formation. This would result in an increase in the number of stars per unit mass of the halo, i.e., in an increase in the efficiency of star formation.     

The thickness of stellar disks in early-type galaxies

We suggest and justify a new photometric method enabling the derivation of the relative thickness of a galactic disk from the two-dimensional surface-brightness distribution of the galaxy in the plane of the sky. The method is applied to images of 45 early-type (S0-Sb) galaxies with known radial exponential or piece-wise-exponential (with a flatter outer profile) surface-brightness distributions. The data were taken from the open SDSS archive. The statistics of the estimated relative thicknesses of the stellar disks of early-type galaxies show the following features. The disks of lenticular and spiral early-type galaxies have similar thickness. The presence of a bar results in only a slight increase of the thickness. However, there is a substantial difference between the thicknesses of disks with a single exponential brightness profile and exponential disks that represent the inner segments of Type III profiles (after Erwin); i.e., they have an outer exponential disk with a larger characteristic scale. The disks are significantly thicker in the former than in the latter case. This may provide evidence that a single exponential scale in a disk surface-brightness distribution forms due to viscosity effects acting over the entire period of star-formation evolution in the disk.     

The nature of precursor waves from distant earthquakes

It is shown that, in accordance with the data used when determining velocity distribution in the Earth’s core [14], so called “precursor” earthquakes cannot be produced by wave scattering to lower mantle inhomogeneities, because seismic rays linking the earthquake sources and seismic stations are located in different inner zones of the Earth and travel at different azimuths, producing a stable wave pattern on aggregate. Thus, the present work considers the fundamental problem regarding what precursor earthquakes are. Solution of this problem will guide ideas about the structure of the Earth’s core.     

The radial gradient of heavy-element abundances in disk galaxies

Various origins for the formation of the heavy-element abundance gradients observed in nearly all disk galaxies are analyzed in the framework of evolutionary models. In an isolated galaxy, there is a radial gradient of the abundance of heavy elements only early in its evolution (the first several billion years), which subsequently practically disappears. The gradients of chemical compositions of young objects and the interstellar gas require that typical disk galaxies be open systems (i.e., that they eject some heavy elements into circumgalactic space and/or accrete intergalactic gas) and that the rates of both processes be dependent on galactocentric distance.     

Numerical estimation of REV and permeability tensor for fractured rock masses by composite element method

The Monte Carlo method is used to generate parent stochastic discrete fracture network, from which a series of fractured rock samples of different sizes and orientations are extracted. The fracture network combined with a regular grid forms composite element mesh of the fractured rock sample, in which each composite element is composed of sub‐elements incised by fracture segments. The composite element method (CEM) for the seepage is implemented to obtain the nodal hydraulic potential as well as the seepage flow rates through the fractured rock samples. The application of CEM enables a large quantity of stochastic tests for the fractured rock samples because the pre‐process is facilitated greatly. By changing the sizes and orientations of the samples, the analysis of the seepage characteristics is realized to evaluate the variation of the permeability components, the existence of the permeability tensor and the representative element volume. The feasibility and effectiveness are illustrated in a numerical example. Copyright © 2008 John Wiley & Sons, Ltd.     

Stellar structure of irregular galaxies: Edge-on galaxies

Stellar photometry obtained using the Hubble Space Telescope is used to study the distributions of the number densities of stars of various ages in 12 irregular and dwarf spiral galaxies viewed edge-on. Two subsystems can be distinguished in all the galaxies: a thin disk comprised of young stars and a thick disk containing a large fraction of old stars (primarily red giants) in the system. Variations of the stellar number density in the thin and thick disks in the Z direction perpendicular to the plane of the galaxy follow an exponential law. The size of the thin disk corresponds to the visible size of the galaxy at the μ = 25 mag/arcsec² isophote, while the thick disk is a factor of two to three larger. In addition to a thick disk, the massive irregular galaxy M82 also has a more extended stellar halo that is flattened at the galactic poles. The results of our previous study of 12 face-on galaxies are used together with the new results presented here to construct an empirical model for the stellar structure of irregular galaxies. Original Russian Text ? N.A. Tikhonov, 2006, published in Astronomicheskiĭ Zhurnal, 2006, Vol. 83, No. 7, pp. 579–588.