Properties of quasar-galaxy associations and gravitational mesolensing by halo objects

A new catalog of 8382 close quasar-galaxy pairs is presented. The catalog was composed using published catalogs of quasars and active galactic nuclei containing 11358 objects, as well as the LEDA catalog of galaxies, which contains on the order of 100 thousand objects. Based on these new data, the dependence of the number of pairs on a=z _G /z _Q is analyzed, where z _G and z _Q are the redshifts of the galaxy and quasar, respectively, revealing an excess of pairs with a<0.1 and a>0.9. This means that the galaxies in pairs are preferably located close to either the observer or the quasar and avoid intermediate distances along the line of sight to the quasar. Computer simulations demonstrate that it is not possible to explain this number of pairs with the observed distribution in a as the result of chance positional coincidences with a uniform spatial distribution of galaxies. Data on globular clusters show that the excess of pairs with a<0.1 and a>0.9 is consistent with the hypothesis that we are observing distant compact objects that are strongly gravitationally lensed by transparent lenses with a King mass distribution located in the halos of nearby galaxies. The Hubble diagram for galaxies and quasars is presented. Observational tests of the mesolensing hypothesis are formulated.     

Type Ia supernovae: Non-standard candles of the universe

We analyze the influence of the evolution of light absorption by gray dust in the host galaxies of type Ia supernovae (SN Ia) and the evolution of the mean combined mass of close-binary carbon-oxygen white dwarfs merging due to gravitational waves (SN Ia precursors) on the interpretation of Hubble diagrams for SN Ia. A significant increase in the mean SN Ia energy due to the higher combined masses of merging dwarfs should be observable at redshifts z > 2. The observed relation between the distance moduli and redshifts of SN Ia can be interpreted not only as evidence for accelerated expansion of the Universe, but also as indicating time variations of the gray-dust absorption of light from these supernovae in various types of host galaxies, observational selection effects, and the decreasing mean combined masses of merging degenerate dwarfs.     

The role of external factors in the evolution of galaxies

We consider the evolution of galaxies in dense galactic clusters. Observations and theoretical estimates indicate that this evolution may be specified to a large extent by collisions between galaxies, as well as interactions between the gaseous components of disk galaxies and intergalactic gas. We analyze collisions between disk galaxies with gaseous components using a simple model based on a comparison of the duration of a collision and the characteristic cooling time for the gas heated by the collision, and also of the relative masses of stars and gas in the colliding disk galaxies. This model is used to analyze scenarios for collisions between disk galaxies with various masses as a function of their relative velocities. Our analysis indicates that galaxies can merge, lose one or both of their gaseous components, or totally disintegrate as a result of a collision; ultimately, a new galaxy may form from the gas lost by the colliding galaxies. Disk galaxies with mass M _G and velocities exceeding ～300 (M _G/10¹⁰ M _⊙)^1/2 km/s in intergalactic gas in clusters with densities ～10^?27 g/cm³ can lose their gas due to the pressure of inflowing intergalactic gas, thereby developing into E(SO) galaxies.     

The Role of Gravitational Radiation in the Evolution of Stars and Galaxies

The conditions for the formation of close binaries containing main-sequence stars, degenerate dwarfs of various types, neutron stars, and black holes of various masses are considered. The paper investigates the evolution of the closest binary systems under the influence of their gravitational-wave radiation. The conditions under which the binary components can merge on a time scale shorter than the Hubble time as a result of their emission of gravitational waves are estimated. A self-consistent scenario model is used to estimate the frequency of such events in the Galaxy, their observable manifestations, the nature of the merger products, and the role of these events in the evolution of stars and galaxies. The conditions for the formation and evolution of supermassive binary black holes during collisions andmergers of galaxies in their dense clusters are studied.

     

Formation of supermassive black holes due to the tidal deceleration of stellar black holes, globular clusters, and galaxies

The formation and evolution of supermassive (10²?10¹⁰ M _⊙) black holes (SMBHs) in the dense cores of globular clusters and galaxies is investigated. The raw material for the construction of the SMBHs is stellar black holes produced during the evolution of massive (25?150M _⊙) stars. The first SMBHs, with masses of ～1000M _⊙, arise in the centers of the densest and most massive globular clusters. Current scenarios for the formation of SMBHs in the cores of globular clusters are analyzed. The dynamical deceleration of the most massive and slowly moving stellar-mass (< 100M _⊙) black holes, accompanied by the radiation of gravitational waves in late stages, is a probable scenario for the formation of SMBHs in the most massive and densest globular clusters. The dynamical friction of the most massive globular clusters close to the dense cores of their galaxies, with the formation of close binary black holes due to the radiation of gravitational waves, leads to the formation of SMBHs with masses ? 10³ M _⊙ in these regions. The stars of these galaxies form galactic bulges, providing a possible explanation for the correlation between the masses of the bulge and of the central SMBHs. The deceleration of the most massive galaxies in the central regions of the most massive and dense clusters of galaxies could lead to the appearance of the most massive (to 10¹⁰ M _⊙) SMBHs in the cores of cD galaxies. A side product of this cascade scenario for the formation of massive galaxies with SMBHs in their cores is the appearance of stars with high spatial velocities (> 300 km/s). The velocities of neutron stars and stellar-mass black holes can reach ～10⁵ km/s.     

An absolute cosmological-distance scale and the peculiar-velocity field from proper motions of galaxies

We suggest a method for extracting important cosmological information from observational data on galaxy proper motions on the celestial sphere. These data can be used to reconstruct the three-dimensional velocities of galaxies relative to the cosmicmicrowave background (peculiar velocities), and to separate the Hubble and peculiar components of the observed redshifts in a large volume for the first time. As a result, it is possible to determine the Hubble constant accurately and independently using the radial velocities of comparatively close galaxies (up to 50 Mpc), and to determine distances to the galaxies and the mass distribution in the neighborhood of the Local group of galaxies. The proposed task may be solved using the future “Millimetron” space radio interferometer.     

Supermassive black holes and galaxy kinematics

The statistical relation between the masses of supermassive black holes (SMBHs) in disk galaxies and the kinematic properties of their host galaxies is analyzed. Velocity estimates for several galaxies obtained earlier at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences and the data for other galaxies taken from the literature are used. The SMBH masses correlate well with the rotational velocities at a distance of R ≈ 1 kpc, V ₁, which characterize the mean density of the central region of the galaxy. The SMBH masses correlate appreciably weaker with the asymptotic velocity at large distances from the center and the angular velocity at the optical radius R ₂₅. We have found for the first time a correlation between the SMBH mass and the total mass of the galaxy within the optical radius R ₂₅, M ₂₅, which includes both baryonic and “dark” mass. The masses of the nuclear star clusters in disk galaxies (based on the catalog of Seth et al.) are also related to the dynamical mass M ₂₅; the correlations with the luminosity and rotational velocity of the disk are appreciably weaker. For a given value of M ₂₅, the masses of the central cluster are, on average, an order of magnitude higher in S0-Sbc galaxies than in late-type galaxies, or than the SMBH masses. We suggest that the growth of the SMBH occurs in the forming “classical” bulge of the galaxy over a time < 10⁹ yr, during a monolithic collapse of gas in the central region of the protogalaxy. The central star clusters form on a different time scale, and their stellar masses continue to grow for a long time after the growth of the central black hole has ceased, if this process is not hindered by activity of the nucleus.     

Dark matter and dark energy in dwarf galaxy systems

Quantitative estimates of themaximumallowed totalmasses and sizes of the dark-matter halos in groups and associations of dwarf galaxies—special types of metagalactic populations identified in recent astronomical observations with the Hubble Space Telescope—are presented. Dwarf-galaxy systems are formed of isolated dark-matter halos with a small number of dark galaxies embedded in them. Data on the sizes of these systems and the velocity dispersions of the embedded galaxies can be used to determine lower limits on the total dark-halo masses using the virial theorem. Upper limits follow from the conditions that the systems immersed in the cosmic dark-energy background be gravitationally bound. The median maximum masses are close to 10¹² M _⊙ for both groups and associations of dwarf galaxies, although the median virial masses for these two types of systems differ by approximately a factor of ten.     

The influence of the decay of OB associations on the evolution of dwarf galaxies

The ejection of stars from spheroidal and disk dwarf galaxies resulting from the decay of OB associations is studied. This has substantial observational consequences for disk galaxies with escape velocities up to 20 km/s, or dynamical masses up to 10⁸ M _⊙. The ejection of stars can (i) reduce the abundances of the products of Type Ia supernovae and, to a lesser degree, Type II supernovae, in disk stars, (ii) chemically enrich the galactic halo and intergalactic medium, (iii) lead to the loss of 50% of the stellar mass in galaxies with masses ∼10⁷ M _⊙ and the loss of all stars in systems with masses ≲10⁵ M _⊙, (iv) increase the mass-to-luminosity ratio of the galaxy.     

Supermassive black holes and central star clusters: Connection with the host galaxy kinematics and color

The relationship between the masses of the central, supermassive black holes (M _bh) and of the nuclear star clusters (M _nc) of disk galaxies with various parameters galaxies are considered: the rotational velocity at R = 2 kpc V ₍₂₎, the maximum rotational velocity V _max, the indicative dynamical mass M ₂₅, the integrated mass of the stellar populationM _*, and the integrated color index B-V. The rotational velocities andmasses of the central objects were taken from the literature. ThemassM _nc correlatesmore closely with the kinematic parameters and the disk mass than M _bh, including with the velocity V _max, which is closely related to the virial mass of the dark halo. On average, lenticular galaxies are characterized by higher massesM _bh compared to other types of galaxies with similar characteristics. The dependence of the blackhole mass on the color index is bimodal: galaxies of the red group (red-sequence) with B-V >0.6–0.7 which are mostly early-type galaxies with weak star formation, differ appreciably from blue galaxies, which have higher values of M _nc and M _bh. At the dependences we consider between the masses of the central objects and the parameters of the host galaxies (except for the dependence of M _bh on the central velocity dispersion), the red-group galaxies have systematically higher M _bh values, even when the host-galaxy parameters are similar. In contrast, in the case of nuclear star clusters, the blue and red galaxies form unified sequences. The results agree with scenarios in which most red-group galaxies form as a result of the partial or complete loss of interstellar gas in a stage of high nuclear activity in galaxies whose central black-hole masses exceed 10⁶?10⁷ M _⊙ (depending on the mass of the galaxy itself). The bulk of disk galaxies with M _bh > 10⁷ M _⊙ are lenticular galaxies (types S0, E/S0) whose disks are practically devoid of gas.     

Giant radio galaxies: Old long-lived quasars?

The properties of giant radio sources (GRS’s) are considered with the aim of identifying conditions contributing to their formation, using data from the literature, the Sloan Digital Sky Survey (SDSS), and the APM catalog. The optical and radio properties of normal-size radio sources, (≤1 Mpc), are compared. The following conclusions are reached. (1) The fraction of objects with broad emission lines among GRS’s with high-excitation spectra is the same as for isotropic samples of radio sources; in the framework of the “unified scheme,” this testifies to an isotropic distribution of angles between the radio jets of GRS’s and the line of sight, i.e., GRS’s do not represent a population of objects whose radio jets are in the plane of the sky. (2) Giant radio sources do not differ from normal radio sources in the distributions of various asymmetry parameters for their extended radio components; in the unified scheme, the similarity of the asymmetry distributions for giant radio galaxies and giant radio quasars suggests that the origin of the asymmetry of their extended radio components is inhomogeneity of the external conditions. (3) The observed powers of the radio jets of giant and normal radio sources do not differ, making it unlikely that the large sizes of the GRS’s are due to this factor. (4) The richness and character of the environments of giant and normal radio sources do not differ: giant host galaxies are found in both isolated fields and in clusters of up to Abell class 1 in richness. This argues against the idea that a low density of the environment is the only origin of GRS’s. (5) The relatively large fraction of radio sources with two pairs of extended radio components (so-called double-double radio sources) among GRS’s testifies that the lifetimes of GRS’s are approximately an order of magnitude longer than those of normal radio sources.Given the equal spatial densities of nearby (z < 0.1) GRS’s and FR II radio sources with powers P _{1.4 MHz} > 10²⁵ W/Hz, this indicates that ∼10% of FR II radio sources have lifetimes an order of magnitude longer, and evolve into GRS’s. (6) The small (∼0.1) ratio of the number of known GRS’s to the number of normal FR II radio sources, together with the observed spatial density of GRS’s at z ∼ 0.6, which is an order of magnitude lower than the predicted value, suggests that a considerable number of GRS’s were missed by surveys at z > 0.1, possibly due to observational selection effects because of their relatively low radio powers and radio surface brightnesses. (7) The absence of “double-double” giant quasars suggests that these objects have a shorter activity time scale than GRS’s. In an evolutionary scenario that is an alternative to the unified scheme uniting “radio loud” quasars and radio galaxies, radio quasars evolve with time into radio galaxies, and the observed relative number of radio quasars among the GRS’s (∼10%) can be interpreted as reflecting the existence of a long-lived population of “radio loud” quasars comprising ∼10% of all radio quasars, with such a population of long-lived radio quasars being the parent population for giant radio galaxies.     

Stellar subsystems of the galaxy NGC 2366

Hubble Space Telescope archive data are used to perform photometry of stars in seven fields at the center and periphery of the galaxy NGC 2366. The variation of the number density of stars of various ages with galactocentric radius and along the minor axis of the galaxy are determined. The boundaries of the thin and thick disks of the galaxy are found. The inferred sizes of the subsystems of NGC 2366 (Z _thin = 4 kpc and Z _thick = 8 kpc for the thin and thick disks, respectively) are more typical for spiral galaxies. Evidence for a stellar halo is found at the periphery of NGC 2366 beyond the thick disk of the galaxy.     

Ocean chemistry during glacial time—a comment

The detection and measurement of CO₂ in air bubbles entrapped in ice originated with Per F. Scholander in 1954, predating the studies referred to in Broecker (1982), Geochim. Cosmochim. Acta 46, 1689–1706.     

Properties of galactic disks at optical and near-IR wavelengths

We have analyzed the radial scales, central surface brightnesses, and colors of 400 disks of various types of galaxies. For nine galaxies, the brightness decrease and the central disk brightness were obtained via a two-dimensional decomposition of the U BV RI J H K photometric images into bulge and disk components. We used published disk parameters for 392 of the galaxies. The central surface brightness μ _0,i ⁰ and linear (disk) scale length h vary smoothly along the Hubble sequence of galaxies within a rather narrow interval. The disks of relatively early-type galaxies display higher central K surface brightnesses, higher central surface densities, higher central mass-to-luminosity ratios M/L(B), smaller sizes (relative to the diameter of the galaxy D ₂₅), redder integrated colors, and redder central colors. The color gradient normalized to the radius of the galaxy and the “blue” central surface brightness of the disk, μ _0,i/0(B), are both independent of the galaxy type. The radial disk scales in different photometric bands differ less in early-type than in late-type galaxies. A correlation between the central disk surface brightness and the total luminosity of the galaxy is observed. We also consider the influence of dust on the photometric parameters of the disks.     

Dynamical evolution of galaxy clusters in the framework of the <Emphasis Type="Italic">N</Emphasis>-body problem. The formation of supermassive cD galaxies

We have carried out numerical simulations of the dynamical evolution of galaxy clusters taking into account merging when the relative velocities of the colliding galaxies are low. In particular, we study the evolution of the structure, mass spectrum, and velocity spectrum of a cluster of a thousand galaxies, as well as the growth of the central supermassive cD galaxy. The initial velocity dispersion of the galaxies and the rotation of the cluster were taken into account. The observed logarithmic spectrum dN ～ \(\tfrac{{dM}}{M}\) was adopted as the initial mass spectrum. The dynamical evolution of galaxy clusters, allowing for the possible merging of colliding galaxies, results in the emergence of a central supermassive galaxy, whose mass continuously increases due to mergers. This occurs only if the mass of the central galaxy becomes greater than ～0.1 of the total mass of the cluster. The observation of cD galaxies with relative masses of ～0.01 suggests that they initially formed in the cluster core, merged with nearby galaxies, and accreted intergalactic gas. The model indicates that a logarithmic galaxy mass spectrum is preserved during the cluster evolution, despite the substantial decrease in the number of galaxies in the cluster with time. The model can also reproduce the observed mass distribution with distance from the cluster center, M _r ～ r ^1.7.     

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.     

Merging of components in close binaries: Type Ia supernovae,massive white dwarfs,and Ap stars

The “Scenario Machine” (a computer code designed for studies of the evolution of close binaries) was used to carry out a population synthesis for a wide range of merging astrophysical objects: main-sequence stars with main-sequence stars; white dwarfs with white dwarfs, neutron stars, and black holes; neutron stars with neutron stars and black holes; and black holes with black holes. We calculate the rates of such events, and plot the mass distributions for merging white dwarfs and main-sequence stars. It is shown that Type Ia supernovae can be used as standard candles only after approximately one billion years of evolution of galaxies. In the course of this evolution, the average energy of Type Ia supernovae should decrease by roughly 10%; the maximum and minimum energies of Type Ia supernovae may differ by no less than by a factor of 1.5. This circumstance must be taken into account at estimating the parameters of the Universe expansion acceleration. According to theoretical estimates, the most massive—as a rule, magnetic—white dwarfs probably originate from mergers of white dwarfs of lower mass. At least some magnetic Ap and Bp stars may form in mergers of low-mass main-sequence stars (M ? 1.5 M _⊙) with convective envelopes.     

The role of dark matter in the dynamical evolution of galaxy clusters in the framework of the <Emphasis Type="Italic">N</Emphasis>-body problem

NumericalN-body studies of the dynamical evolution of a cluster of 1000 galaxies were carried out in order to investigate the role of dark matter in the formation of cD galaxies. Two models explicitly describing the darkmatter as a full-fledged component of the cluster having its own physical characteristics are constructed. These treat the dark matter as a continuous underlying substrate and as “grainy” matter. The ratio of the masses of the dark and luminous matter of the cluster is varied in the range 3–100. The observed logarithmic spectrum dN ∼ dM / M is used as an initial mass spectrum for the galaxies. A comparative numerical analysis of the evolution of the mass spectrum, the dynamics of mergers of the cluster galaxies, and the evolution of the growth of the central, supermassive cD galaxy suggests that dynamical friction associated with dark matter accelerates the formation of the cD galaxy via the absorption of galaxies colliding with it. Taking into account a dark-matter “substrate” removes the formation of multiple mass-accumulation centers, and makes it easier to form a cD galaxy that accumulates 1–2% of the cluster mass within the Hubble time scale (3–8 billion years), consistent with observations.     

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.