Modeling the mass-metallicity relation for dSph dwarf galaxies of the local group

The relationship between the masses and metallicities of galaxies could be non-monotonic, due to the outflow of matter in these systems. It is shown using a simple, one-zone, chemical-dynamicalmodel that the metallicity should be a non-monotonic function of the mass for spheroidal dwarf galaxies with low masses of M ≤ 10⁸ M _⊙, and a monotonically growing function for galaxies with higher masses. This is consistent with observations.     

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.     

Multicolor CCD photometry of six lenticular and spiral galaxies. Structure of the galaxies

The results of multicolor surface photometry of the S0 galaxies NGC 524, NGC 1138, and NGC 7280 and the spiral galaxies NGC 532, NGC 783, and NGC 1589 are reported. U BV RI observations were acquired with the 1.5-m telescope of the Maidanak Observatory (Uzbekistan), while JHK data were taken from the 2MASS catalog. The overall structure of the galaxies is analyzed and the galaxy images decomposed into bulge and disk components. The parameters of the galaxy components—rings, bars, spiral arms, and dust lanes—are determined. The bulge/disk decompositions based on averaged one-dimensional photometric profiles yield incorrect parameters for the bulges of the S0-Sa galaxies with bars and/or rings, whose inner regions are dominated by the radiation of the bulge.     

Multicolor CCD photometry of six lenticular and spiral galaxies. Stellar population of the galaxies

The results of multicolor surface photometry of the S0 galaxies NGC 524, NGC 1138, and NGC 7280 and the spiral galaxies NGC 532, NGC 783, and NGC 1589 are analyzed. UBVRI observations were acquired with the 1.5-m telescope of the Maidanak Observatory (Uzbekistan), while JHK data were taken from the 2MASS catalog. The brightness and color distributions in the galaxies are analyzed. Extinction in dust lanes in three spiral galaxies is estimated. The contributions of the radiation of the spherical and disk components in different photometric bands are estimated. Two-color diagrams are used to estimate the composition of the stellar populations in various galaxy components. The variations of the color characteristics in the S0 galaxies is due mostly to radial metallicity gradients.     

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.     

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 catalog of galaxies in and around the cluster A1367. Spectral studies of several galaxies

We present a catalog of galaxies in and around the cluster A1367, together with the results of a spectroscopic study of eight faint galaxies projected onto the central part of the cluster. The observations were carried out with the Boller and Chivens spectrograph of the 2m telescope of the Guillermo Haro Observatory (Cananea, Mexico). Redshifts of eight galaxies were derived from both emission and absorption lines; the redshift for one of these, derived from Hα, SII, OIII, and Hβ emission lines, is z = 0.015. The spectrum of this galaxy displays no absorption lines at z = 0.026, testifying that it is located between the observer and A1367.     

The cosmic vacuum and the rotation of galaxies

The rotational effect of the cosmic vacuum is investigated. The induced rotation of elliptical galaxies due to the anti-gravity of the vacuum is found to be 10⁻²¹ s⁻¹ for real elliptical galaxies. The effect of the vacuum rotation of the entire Universe is discussed, and can be described by the invariant ω _ν = ω ₀ ∼ $ \sqrt {G\rho v} $ \sqrt {G\rho v} . The corresponding numerical angular velocity of the Universe is 10⁻¹⁹ s⁻¹, in good agreement with modern data on the temperature fluctuations of the cosmic background radiation.     

Long gamma-ray bursts and the morphology of their host galaxies

We present the results of population syntheses for binary stars carried out using the “Scenario Machine” code with the aim of analyzing events that may result in long gamma-ray bursts. We show that the observed distribution of morphological types of the host galaxies of long gamma-ray bursts can be explained in a model in which long gamma-ray bursts result from the core collapse of massive Wolf-Rayet stars in close binaries. The dependence of the burst rate on galaxy type is associated with an increase in the rate of stellar-wind mass-loss with increasing stellar metallicity. The separation of binary components at the end of their evolution increases with the stellar-wind rate, resulting in a reduction of the number of binaries that produce gamma-bursts.     

Evolution of the star-formation rate and extinction in disk galaxies at high <Emphasis Type="Italic">z</Emphasis>

A model for the evolution of disk galaxies is used to investigate evolutionary variations in the star-formation rate (SFR) and extinction in disk galaxies beginning from their formation. The results obtained are compared with observational estimates of the SFRe and extinction at cosmological redshifts z ≤ 7. The formof themass-radius relation for disk galaxies is discussed. It is proposed that the mass-radius relation is a consequence of a mass-angular momentum relation. Analysis of the influence of the form of the mass-radius relation on the evolutionary variations in the SFR and extinction testify that this influence is very small. The SFRs and extinctions at various redshifts z obtained in the models are in agreement with observations.     

The star-formation efficiency and density of the disks of spiral galaxies

The four well studied spiral galaxies M33, M81, M100, and M101 are used to analyze the dependences of the star-formation rate (SFR) and star-formation efficiency (SFE = SFR/M _gas ) on galactocentric distance R and the photometric and some kinematic parameters of galactic disks. The dependences SFR(R) were estimated based on UV and far-infrared data using published extinction-corrected UV brightness profiles of the galaxies. The local SFE values are most closely related to the surface brightness (density) of the galactic disk at a given R, with this dependence being the same for all four galaxies (except for their central regions). In order to explain the observed disk densities in terms of a simple conservative model (“toy model”) for the evolution of the gas density, the local value of the parameter N in the Schmidt law for the disk (SFR ～ σ _gas ^N ) must not exceed unity. In this case, the observed dependences σ _gas (R) and SFE(R) can be matched assuming that accretion is occuring in the central regions of the disks.     

Polygonal structure of spiral galaxies

We have carried out numerical simulations of hydrodynamical processes occurring in the disks of spiral galaxies. The initial state of the disk is an equilibrium stellar-gaseous configuration. The spherical component is described by a standard analytical model for the gravitational potential. The behavior of the modeled disk in the presence of an external perturbation is analyzed. The results of numerical simulations of stellar-gaseous galactic disks aimed at studying the formation of polygonal structures in spiral galaxies are presented. The possible influence of spur-like formations on the appearance of polygonal structure is studied.     

The stellar population and evolution of galaxies of the NGC 80 group

Seven early-type galaxies that are members of the massive X-ray group containing NGC 80 have been studied using two-dimensional spectroscopy with the 6-m telescope of the Special Astrophysical Observatory. We searched for evidence for the synchronous secular evolution of the galaxies in the group. The bulges of five of the seven galaxies appear to be old, with the average age of the bulge stars being 10–15 billion years. Signs of a relatively recent star-formation burst are observed in the small S0 galaxy IC 1548, whose average bulge age is 3 billion years and average core age is 1.5 billion years. A circumnuclear polar gas ring was also detected in this galaxy; in its outer regions, it makes a smooth transition to a gas disk that counter-rotates relative to the stars. IC 1548 probably underwent a close interaction, which resulted in its transformation from a spiral to a lenticular galaxy; the same interaction may also have induced the central burst of star formation. In the giant E0 galaxy NGC 83, a compact massive stellar-gas disk with a radius of about 2 kpc and very rapid rotation is observed, with ongoing star formation; the so-called “minor merger” is likely to have occurred there. We conclude that the NGC 80 group is in a state of formation, with the small NGC 83 subgroup “falling into” the large, old NGC 80 subgroup.     

The zero-acceleration surface around the Local Group of galaxies

Recent observational data on the density of the cosmic vacuum are used to obtain an exact solution for the zero-acceleration surface around the Local Group of galaxies. This surface separates the inner region, in which the gravitation of the galaxies dominates, from the outer region, in which the antigravitation of the cosmic vacuum dominates. The zero-acceleration surface is close to a sphere of radius ?2 Mpc. The size and shape of the surface have remained nearly constant during the lifetime of the Local Group as a distinct system of galaxies.     

Dynamics and stability of resonant rings in galaxies

We have developed a model for a spheroidal, ring-shaped galaxy. The stars move in a ring with an elliptical cross section at the 1: 1 frequency resonance. The shape of the cross section of the equilibrium ring depends on the oblateness of the galaxy itself, so that the ellipse of the ring cross section is radially extended when the oblateness of the galaxy is small. If the oblateness of galaxy exceeds some critical value, the ellipse cross section is extended along the Ox ₃ axis. The shape of the ring cross section is circular for a galaxy with critical eccentricity. The stability of the ring over a wide range of perturbations is studied. A fundamental bicubic dispersion equation for the frequencies of small oscillations of a perturbed ring is derived. Application of the model to the ring galaxy NGC 7020 shows that its ring cross section should be approximately circular. Analysis of the dispersion equation demonstrates that stellar orbits in the arm are unstable (but the instability increment is small). We conclude that stars in the ring of this galaxy should drift from the 1: 1 resonance, and the ring itself should evolve.     

Some physical properties of UV galaxies

Observational data on galaxies displaying ultraviolet excesses in their spectra included in a survey compiled at the Byurakan Astrophysical Observatory are considered and discussed. The characteristic physical properties of active galaxies with UV excesses are considered, as well as the unusual morphologies in their central regions. In spite of numerous studies of these galaxies, their physical nature remains incompletely understood. The results of the analysis of the problems associated with the peculiarities of UV galaxies are presented.     

Dark energy in flows of galaxies

It has traditionally been taken for granted that Hubble’s law is the key relation in cosmology, while it is surprisingly mysterious on the local scales of 1–30 Mpc where it was originally discovered. The progress in observational cosmology and, in particular, the discovery of dark energy have changed the views, and now we see that Hubble’s law works hardly at truly cosmological distances, but it rules very well on local scales. Recent observations with the HST, in combination with a theory model of the local expansion flows, give a clear evidence to the presence of dark energy in the local universe. It is dark energy that dominates the dynamics of the local flows and introduces to them the approximately linear velocity-distance relation with nearly universal expansion time-rate.     

Photometric properties of bars in galaxies

We have used surface photometry data for 100 barred galaxies to determine the UBVRIJHK surface brightnesses and color indices for the bars. Two peaks are observed in the distribution of the average bar B brightnesses: at 21.0^m/arcsec² and 22.2^m/arcsec², characteristic of late-and early-type galaxies, respectively. The average surface-brightness difference between the bar and the galaxy (within the 25.0^m/arcsec² isophote) increases from 1.1^m/arcsec² for SB0 galaxies to 2.3^m/arcsec² for SBc-IBm galaxies. In (U-B)₀-(B-V)₀, (B-V ₀-(V-R ₀, and (B-V)₀-(V-I)₀ two-color diagrams, for all morphological types, the bars are shifted leftward from normal color sequence for galaxies. This deviation is more pronounced for the outer than for the inner regions of the bars. Using evolutionary models, we show that this deviation is due to the scarcity of intermediate-age [(1–9)×10⁹ yrs] stars in bars. Possible origins for this anomalous composition of the stellar population are discussed.     

Early-type disk galaxies: Structure and kinematics

Spectroscopic observations of three lenticular (S0) galaxies (NGC 1167, NGC 4150, and NGC 6340) and one SBa galaxy (NGC 2273) have been taken with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences aimed to study the structure and kinematic properties of early-type disk galaxies. The radial profiles of the stellar radial velocities and the velocity dispersion are measured. N-body simulations are used to construct dynamical models of galaxies containing a stellar disk, bulge, and halo. The masses of individual components are estimated formaximum-mass disk models. A comparison of models with estimated rotational velocities and the stellar velocity dispersion suggests that the stellar disks in lenticular galaxies are “overheated”; i.e., there is a significant excess velocity dispersion over the minimum level required to maintain the stability of the disk. This supports the hypothesis that the stellar disks of S0 galaxies were subject to strong gravitational perturbations. The relative thickness of the stellar disks in the S0 galaxies considered substantially exceed the typical disk thickness of spiral galaxies.     

The motions of galaxies in the field of the cosmic vacuum

The general solution and general integral of the equations of motion in the field of the cosmic vacuum are constructed. It is shown that the resulting motions of galaxies are along either hyperbolic or rectilinear paths. The laws of motion of galaxies in the field of the cosmic vacuum are formulated. Various forms of the Hubble law are considered. A strict adherence to the Hubble law is not possible for most initial conditions in the sense of the Lebesgue measure. Therefore, it becomes meaningless to search for explanations to deviations from the Hubble law due to any physical factor, apart from the repulsive force of the cosmic vacuum. Phase portraits for the galaxy motions are constructed. It is shown that the Hubble constant should be determined observationally using the most distant galaxies, since the accuracy of the result will be reduced otherwise.