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1.
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
2.
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
3.
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
4.
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. 相似文献
5.
Possible orbits for the motion of a region in the gravitational field of the central body of the galaxy NGC 4151 are presented.
The region is manifest through its line emission, observed in the red wing of the Hα, Pβ, and other broad lines. We carried out a computer selection of all Keplerian orbits for which the measured radial velocities
of the emission-line region could be observed. We used radial-velocity data obtained by us at the Fesenkov Astrophysical Institute,
as well as data from the literature. The computation results can be used to determine the mass range for the central body
of NGC 4151 that provides the best agreement with the observational data: (61–65)× 106
M
⊙. Suitably designed monitoring of active galactic nuclei can be used to verify these results, and to carry out similar analyses
for other Seyfert galaxies. 相似文献
6.
A. D. Chernin P. Teerikorpi V. P. Dolgachev A. A. Kanter L. M. Domozhilova M. J. Valtonen G. G. Byrd 《Astronomy Reports》2012,56(9):653-663
Outward flows of galaxies are observed around groups of galaxies on spatial scales of about 1 Mpc, and around galaxy clusters on scales of 10 Mpc. Using recent data from the Hubble Space Telescope (HST), we have constructed two synthetic velocity-distance phase diagrams: one for four flows on galaxy-group scales and the other for two flows on cluster scales. It has been shown that, in both cases, the antigravity produced by the cosmic dark-energy background is stronger than the gravity produced by the matter in the outflow volume. The antigravity accelerates the flows and introduces a phase attractor that is common to all scales, corresponding to a linear velocity-distance relation (the local Hubble law). As a result, the bundle of outflow trajectories mostly follow the trajectory of the attractor. A comparison of the two diagrams reveals the universal self-similar nature of the outflows: their gross phase structure in dimensionless variables is essentially independent of their physical spatial scales, which differ by approximately a factor of 10 in the two diagrams. 相似文献
7.
Results of numerical simulations of a collision of the gaseous components of two identical disk galaxies during a head-on
collision of the galaxies in the polar direction are presented. When the relative velocity of the galaxy collision is small,
their gaseous components merge. At high relative velocities (100–500 km/s), the massive stellar components of the galaxies
(M
g
= 109
M
⊙) pass through each other nearly freely, leaving behind the gaseous components, which are decelerated and heated by the collision.
If the overall gaseous component of the colliding galaxies is able to cool to the virial temperature during the collision,
a new galaxy forms. At velocities V ≥ 500 km/s, the gaseous component does not have time to cool, and the gas is scattered into intergalactic space, supplying
it with heavy elements produced in supernovae in the colliding galaxies. High-velocity (V ≥ 100 km/s) collisions of identical low-mass galaxies (M
g
≤ 109
M
⊙) whose mass is dominated by the mass of gas lead to the disruption of their stellar components. The overall gaseous component
forms a new galaxy when V ≤ 500 km/s, and is scattered into intergalactic space if the velocity becomes higher than this. A galaxy collision increases
the star-formation rates in the disk galaxies by nearly a factor of 100. Rotation of the colliding galaxies in the same direction
increases the changes of the disruption of both the stellar and gaseous components of the galaxies. The merger of galaxies
during their collision can explain the presence of gaseous disks rotating opposite to the rotation of the stellar component
in some ordinary elliptical galaxies. Moreover, galaxy mergers can help explain the origin of a comparatively young stellar
population in some elliptical galaxies. 相似文献
8.
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. 相似文献
9.
Numerical simulations of the chemical evolution of disk galaxies taking into account the influence of Population III stars
are considered. The probability that stars with peculiar chemical compositions are present in the solar neigborhood is analyzed,
and possibilities for their detection considered. For various assumptions about the slope of the initial mass function for
Population III stars and the critical metallicity, the radius surrounding the Sun containing at least one such star is 10–12
pc. Such objects could be studied using modern large telescopes. The influence of Population III stars on the chemical evolution
of disk galaxies is investigated. Taking into account the first stars in early stages leads to an earlier onset of chemical
enrichment of the ISM and a characteristic chemical composition of the gas, but all traces of this enrichment have disappeared
by the current epoch. 相似文献
10.
A. V. Tutukov 《Astronomy Reports》2006,50(6):439-450
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. 相似文献
11.
N. A. Tikhonov 《Astronomy Reports》2006,50(7):517-525
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. 相似文献
12.
Two-color photometric data obtained on the 6-m telescope of the Special Astrophysical Observatory are used to analyze the
structure of 13 large disk galaxies in the NGC 80 group. Nine of the 13 studied galaxies are classified as lenticular galaxies.
The stellar populations in the galaxies are very diverse, from old stars with ages of T > 10 billion years (IC 1541) to relatively young stars with ages of T ∼ 1–3 billion years (IC 1548, NGC 85); in one case, star formation is ongoing (UCM 0018+2216). In most of the studied galaxies,
more precisely in all of them brighter than M
B ∼ −18, two-tiered stellar disks are detected, whose radial surface-brightness profiles can be described by two exponential
segments with different characteristic scales—shorter near the center and longer at the periphery. All of the dwarf S0 galaxies
with single-tiered disks are close companions to larger galaxies. Except for this fact, no dependence of the properties of
S0 galaxies on distance from the center of the group is found. Morphological signs of a “minor merger” are found in the lenticular
galaxy NGC 85. Based on these last two results, it is concluded that the most probable mechanism for their transformation
of spiral into lenticular galaxies in groups is gravitational (minor mergers and tidal interactions). 相似文献
13.
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. 相似文献
14.
We list and analyze the main currently known mechanisms for accelerating the space motions of stars. A high space velocity
of a star can be a consequence of its formation in the early stages of the evolution of a massive galaxy, when it was spheroidal
and non-stationary, so that stars were born with velocities close to the escape velocity for the galaxy. Another possibility
is that the star arrived from another galaxy with a velocity that is high for our Galaxy. The decay of unstable close multiple
stars or supernova explosions in close binaries can also provide velocities of up to several hundreds of km/s to main-sequence
stars and velocities of up to ∼1000 km/s to degenerate stars, neutron stars, and stellar-mass black holes. The merger of components
of a binary system containing two neutron stars or a neutron star and a black hole due to gravitational-wave radiation can
accelerate the nascent black hole to a velocity∼1000 km/s. Hypervelocity relativistic stars can be born due to asymmetric
neutrino ejection during a supernova explosion. Stars can be efficiently accelerated by single and binary supermassive black
holes (with masses from several millions to several billions of solar masses) in the nuclei of galaxies. Thanks to their gravitational
field and fast orbital motion (in the case of binary objects), supermassive black holes are able to accelerate even main-sequence
stars to relativistic velocities. 相似文献
15.
T. Petrushevska T. Okamura R. Kawamata L. Hangard G. Mahler A. Goobar 《Astronomy Reports》2018,62(12):917-925
Measuring time delays from strongly lensed supernovae (SNe) is emerging as a novel and independent tool for estimating the Hubble constant (H0). This is very important given the recent discord in the value of H0) from two methods that probe different distance ranges. The success of this technique will rely of our ability to discover strongly lensed SNe with measurable time delays. Here, we present the magnifications and the time delays for the multiply-imaged galaxies behind the Hubble Frontier Fields (HFF) galaxy clusters, by using recently published lensing models. Continuing on our previous work done for Abell 1689 (A1689) and Abell 370, we also show the prospects of observing strongly lensed SNe behind the HFF clusters with the upcoming James Webb Space Telescope (JWST). With four 1-hour visits in one year, the summed expectations of all six HFF clusters are ~0.5 core-collapse (CC) SNe and 0.06 Type Ia SNe (SNe Ia) in F115W band, while with F150W the expectations are higher, ~0.9 CC SNe and ~0.06 SNe Ia. These estimates match those expected by only surveying A1689, proving that the performance of A1689 as gravitational telescope is superior. In the five HFF clusters presented here, we find that F150W will be able to detect SNe Ia (SNe IIP) exploding in 93 (80) pairsmultiply-imaged galaxies with time delays of less than 5 years. 相似文献
16.
E. P. Kurbatov 《Astronomy Reports》2010,54(7):590-598
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. 相似文献
17.
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
18.
S. F. Rahman 《Astronomy Reports》2020,64(4):281-294
This paper constraints dynamic dark energy equation of state (EoS) parameters using the type Ia supernovae from Union 2.1 dataset. The paper also discusses the dependency of dynamic dark energy EoS parameters on the chosen or assumed value of the Hubble Constant. To understand the correlation between the Hubble Constant values and measured dynamic dark energy EoS parameters, we used recent surveys being done through various techniques such as cosmic microwave background studies, gravitational waves, baryonic acoustic oscillations and standard candles to set values for different Hubble Constant values as fixed parameters with CPL and WCDM models. Then we applied trust region reflective (TRF) and dog leg (dogbox) algorithms to fit dark energy density parameter and dynamic dark energy EoS parameters. We found a significant negative correlation between the fixed Hubble Constant parameter and measured EoS parameter, $${{w}_{0}}$$. Then we used two best fit Hubble Constant values (70 and 69.18474) km s–1 Mpc–1 based on Chi-square test to test more dark energy EoS parameters like: JBP, BA, PADE-I, PADE-II, and LH4 models and compared the results with $$\Lambda $$-CDM with constant $${{w}_{{{\text{de}}}}} = - 1$$, WCDM and CPL models. We conclude that flat $$\Lambda $$‑CDM and WCDM models clearly provide best results while using the BIC criteria as it severely penalizes the use of extra parameters. However, the dependency of EoS parameters on Hubble Constant value and the increasing tension in the measurement of Hubble Constant values using different techniques warrants further investigation into looking for optimal dynamic dark energy EoS models to optimally model the relation between the expansion rate and evolution of dark energy in our universe. 相似文献
19.
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
20.
The history of the discovery of hot gas in galaxies is briefly reviewed, and the main properties of this gas described, emphasizing the need to refine these properties, in particular, the mass of the gas. It is proposed to do this via observations of the Sunyaev-Zel’dovich (SZ) effect due to hot gas in the coronas of elliptical galaxies. The absolute and relative perturbations of the spectrum of the cosmic microwave background (CMB) radiation due to scattering of the CMB photons by electrons with a Maxwellian energy distribution are calculated. The possibility of observing the SZ effect is demonstrated using three elliptical galaxies as examples. The kinematic SZ effect arising due to the peculiar motions and rotations of the galaxies is also accessible to observations. Together with X-ray data, such observations would enable refinement of the properties of gas in galaxies, and also yield additional information about the rotation of galaxies, possible accretion flows in the galactic gas, and hot galactic winds. 相似文献