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1.
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. 相似文献
2.
We have analyzed the spatial distribution of galaxies from the latest release of the Sloan Digital Sky Survey of galactic
redshifts (SDSS DR7), applying the complete correlation function (conditional density), two-point conditional density (cylinder),
and radial density methods. Our analysis demonstrates that the conditional density has a power-law form for scales lengths
0.5–30 Mpc/h, with the power-law corresponding to the fractal dimension D = 2.2 ± 0.2; for scale lengths in excess of 30 Mpc/h, it enters an essentially flat regime, as is expected for a uniform distribution of galaxies. However, in the analysis applying
the cylinder method, the power-law character with D = 2.0 ± 0.3 persists to scale lengths of 70 Mpc/h. The radial density method reveals inhomogeneities in the spatial distribution of galaxies on scales of 200 Mpc/h with a density contrast of two, confirming that translation invariance is violated in the distribution of galaxies to 300
Mpc/h, with the sampling depth of the SDSS galaxies being 600 Mpc/h. 相似文献
3.
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. 相似文献
4.
We discuss recently published data indicating that the nearby galaxy group NGC 1023 includes an inner, virialized, quasi-stationary
component together with an outer component comprising a flow of dwarf galaxies falling toward the center of the system. The
inner component is similar to the Local Group of galaxies, but the Local Group is surrounded by a receding set of dwarf galaxies
forming the local Hubble flow, rather than a system of approaching dwarfs. This clear difference in the structures of these
two systems, which are very similar in other respects, may be associated with the dark energy in which they are immersed.
Self-gravity dominates in the inner component of the Local Group, while the anti-gravity created by the cosmic dark-energy
background dominates in the surrounding Hubble flow. In contrast, self-gravity likewise dominates throughout the NGC 1023
Group, both in its central component and in the surrounding “anti-Hubble” flow. NGC 1023 as a whole is apparently in an ongoing
state of formation and virialization. We expect that there exists a receding flow similar to the local Hubble flow at distances
of 1.4–3 Mpc from the center of the group, where anti-gravity should become stronger than the gravity of the system. 相似文献
5.
N. A. Tikhonov 《Astronomy Reports》2018,62(10):637-647
Stellar photometry of 53 low-mass spiral and irregular galaxies has been carried out using archival frames obtained by the Hubble Space Telescope. Young and old stars (blue supergiants and red giants) are distinguished on the resulting Hertzsprung–Russell diagrams, and the spatial sizes of the subsystems formed by these stars are determined. A correlation is found between the metallicities of red giants and the difference between the linear sizes of stellar systems of different ages. This dependence can be explained if the sizes of stellar subsystems expand over the lifetimes of galaxies, as well as the influence of the relationship between the mass of a galaxy and the metallicity of its stars. 相似文献
6.
A new class of metagalactic system—wide triple systems of galaxies with characteristic scale lengths of ～1 Mpc—are analyzed. Dynamical models of such systems are constructed, and the amount of dark mass contained in them is estimated. In principle, kinematic data for wide triplets allow two types of models: with individual galactic halos and with a common halo for the entire system. A choice between the two models can be made based on X-ray observations of these systems, which can determine whether clustering and hierarchical evolution continues on scales of ～1 Mpc or whether systems with such scale lengths are in a state of virial quasi-equilibrium. 相似文献
7.
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. 相似文献
8.
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. 相似文献
9.
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. 相似文献
10.
E. S. Safonova 《Astronomy Reports》2011,55(11):1016-1024
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. 相似文献
11.
L. G. Lyk’yanov 《Astronomy Reports》2009,53(1):9-18
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. 相似文献
12.
S. Straub 《International Journal of Earth Sciences》1996,85(1):85-91
Based on the assumption that high-speed high-concentration sediment mass flows are primarily granular flows, their dynamic properties were studied. Such highly sheared granular flows are characterized by interparticle collisions. This so-called rapid granular flow regime has been analysed using two-dimensional computer simulations. It is shown that granular flows at the microstructural level are governed by deterministic chaos. The bulk behaviour is characterized by self-organization and an attractor controlling the energy dissipation of the flow. The existence of this rapid granular flow attractor easily explains the linear relation between drop height and travel distance of debris flows. A compelling consequence of the attractor is that rapid granular flow is the major flow regime in debris flows. 相似文献
13.
N. A. Tikhonov 《Astronomy Reports》2005,49(7):501-509
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 25m/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. 相似文献
14.
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. 相似文献
15.
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.
相似文献16.
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. 相似文献
17.
Observational data on the evolution of quasars and galaxies of various morphological types and numerical simulations carried out by various groups are used to argue that low-redshift (z < 0.5) quasars of types I and II, identified with massive elliptical and spiral galaxies with classical bulges, cannot be undergoing a single, late phase of activity; i.e., their activity cannot be “primordial,” and must have “flared up” at multiple times in the past. This means that their appearance at low z is associated with recurrence of their activity—i.e., with major mergers of gas-rich galaxies (so-called wet major mergers)—since their lifetimes in the active phase do not exceed a few times 107 yrs. Only objects we have referred to earlier as AGN III, which are associated with the nuclei of isolated, late-type spiral galaxies with low-mass, rapidly-rotating “pseudobulges,” could represent primordial AGNs at low z. The black holes in such galaxies have masses M BH < 107 M ⊙, and the peculiarities of their nuclear spectra suggest that they may have very high specific rotational angular momenta per unit mass. Type I narrow-line (widths less than 2000 km/s) Seyfert galaxies (NLSyIs) with pseudobulges and black-hole masses M BH < 107 M ⊙ may be characteristic representatives of the AGN III population. Since NLSyI galaxies have pseudobulges while Type I broad-line Seyfert galaxies have classical bulges, these two types of galaxies cannot represent different evolutionary stages of a single type of object. It is possible that the precursors of NLSyIs are “Population A” quasars. 相似文献
18.
The paper analyzes possible origins of stars located in intergalactic space that are not bound to specific galaxies, which
comprise 15–50% of all stars in galaxy clusters. Some such stars can form in streams of intergalactic gas flowing around gas-rich
disk galaxies moving in the cluster. Others may be the products of the decay of young, low-mass, spheroidal galaxies after
the loss of their gaseous components during an initial burst of star formation. The decay of low-mass disk galaxies moving
at high speeds after they have lost their gaseous components due to the pressure of the incident flow of dense intergalactic
gas is possible in the cluster core. The largest fraction of intergalactic stars are probably produced by the partial disruption
of galaxies as a result of close passages, collisions, or mergers. Collisions of low-mass, gas-rich galaxies are especially
good suppliers of intergalactic stars. Both stars from decaying stellar components of galaxies and stars arising in the gaseous
components of colliding galaxies can be supplied to the intergalactic medium. The merger of galaxies harboring supermassive
black holes in their nuclei could lead to the partial or total disruption of these galaxies during the deceleration of the
binary black hole that is formed during the merger. An enhanced density of intergalactic stars is observed in the cores of
galaxy clusters, underscoring the role of galaxy collisions in the formation of the intergalactic stellar population, since
the frequency of galaxy collisions grows with their density. 相似文献
19.
A. S. Gusev 《Astronomy Reports》2007,51(1):1-18
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. 相似文献
20.
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. 相似文献