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1.
Summary. Due to the foreground extinction of the Milky Way, galaxies appear increasingly fainter the closer they lie to the Galactic
Equator, creating a “zone of avoidance” of about 25% in the distribution of optically visible galaxies. A “whole-sky” map
of galaxies is essential, however, for understanding the dynamics in our local Universe, in particular the peculiar velocity
of the Local Group with respect to the Cosmic Microwave Background and velocity flow fields such as in the Great Attractor
region.
Various dynamically important structures behind the Milky Way have only recently been made “visible” through dedicated deep
surveys at various wavelengths. The wide range of observational searches (optical, near infrared, far infrared, radio and
X-ray) for galaxies in the Zone of Avoidance are reviewed, including a discussion on the limitations and selection effects
of these partly complementary approaches. The uncovered and suspected large-scale structures are summarized. Reconstruction
methods of the density field in the Zone of Avoidance are described and the resulting predictions compared with observational
evidence. The comparison between reconstructed density fields and the observed galaxy distribution allow derivations of the
density and biasing parameters and b.
Received 4 April 2000 / Published online 18 July 2000 相似文献
2.
O. G. Kashibadze 《Astrophysics》2008,51(3):336-348
The peculiar velocity field for 907 galaxies with heliocentric radial velocities VH ≤ 3000 km/s is examined. The data are divided into three samples, organized according to the principles behind the method
for determining the distance to the galaxies: the luminosity of the tip of the red giant branch (TRGB), fluctuations in the
surface brightness, and the infrared Tully-Fisher relation for spiral galaxies viewed edge-on. The latter sample includes
410 galaxies. For determining the distance to the galaxies in this sample, additional regressors were introduced into the
Tully-Fisher relation, in particular the “color index” K-m21, which make it possible significantly to reduce the dispersion with respect to the regression curve. All three samples showed
good agreement in the peculiar velocity distribution. Based on each of these samples, as well as on the combined sample, detailed
maps of the field of peculiar velocities of the galaxies are constructed for VH ≤ 3000 km/s. An analysis shows that most of the observed features of this map can be explained by large-scale density variations
in the galactic distribution.
__________
Translated from Astrofizika, Vol. 51, No. 3, pp. 409–422 (August 2008). 相似文献
3.
I. D. Karachentsev D. I. Makarov V. E. Karachentseva O. V. Melnyk 《Astrophysical Bulletin》2011,66(1):1-27
We present a catalog of 520 most isolated nearby galaxies with angular velocities V
LG
< 3500 km/s, covering the entire sky. This population of “space orphans” makes up 4.8% among 10 900 galaxies with measured
radial velocities. We describe the isolation criterion used to select our sample, called the “Local Orphan Galaxies”(LOG),
and discuss their basic optical and HI properties. A half of the LOG catalog is occupied by the Sdm, Im and Ir morphological
type galaxies without a bulge. The median ratio M
gas/M
star in the LOG galaxies exceeds 1. The distribution of the catalog galaxies on the sky looks uniform with some signatures of
a weak clustering on the scale of about 0.5 Mpc. The LOG galaxies are located in the regions where the mean local density
of matter is approximately 50 times lower than the mean global density. We indicate a number of LOG galaxies with distorted
structures, which may be the consequence of interaction of isolated galaxies with massive dark objects. 相似文献
4.
O. V. Abramova 《Astronomy Letters》2012,38(4):222-230
Observations of neutral hydrogen in spiral galaxies reveal a sharp cutoff in the radial density profile at some distance from
the center. Using 22 galaxies with known HI distributions as an example, we discuss the question of whether this effect can
be associated exclusively with external ionizing radiation, as is commonly assumed. We show that before the surface density
reaches δ
HI ≤ 0.5 M
⊙ pc−2 (the same for galaxies of different types), it is hard to expect the gas to be fully ionized by background radiation. For
two of 13 galaxies with a sharp drop in the HI profile, the “steepening” can actually be caused by ionization. At the same
time, for the remaining galaxies, the observed cutoff in the radial HI profile is closer to the center than if it was a consequence
of ionization by background radiation and, therefore, it should be caused by other factors. 相似文献
5.
Groups of galaxies are identified on the basis of the CfA2 redshift survey and a method proposed by one of the authors. Of
the 15577 galaxies that have redshifts of 1000-15000 km/s and lie at galactic latitudes |bII| ≥ 20° , 1971 groups with n ≥
2 members were found, with a combined total number of 6787 members. The remaining 8790 (56.4%) galaxies constitute a sample
of “single,” isolated galaxies. The dispersion in the radial velocities of the groups and their radii are found to depend
weakly on the distance to the observer. 相似文献
6.
7.
Sidney van den Bergh 《Astronomy and Astrophysics Review》1999,9(3-4):273-318
Summary. Hubble's (1936, p. 125) view that the Local Group (LG) is “a typical, small group of nebulae which is isolated in the general
field” is confirmed by modern data. The total number of certain and probable Group members presently stands at 35. The half-mass
radius of the Local Group is found to be kpc. The zero-velocity surface, which separates the Local Group from the field that is expanding with the Hubble flow, has
a radius Mpc. The total mass of the LG is . Most of this mass appears to be concentrated in the Andromeda and Milky Way subgroups of the LG. The total luminosity of
the Local Group is found to be :. This yields a mass-to-light ratio (in solar units) of . The solar motion with respect to the LG is \,km s, directed towards an apex at , and . The velocity dispersion within the LG is km s. The galaxies NGC 3109, Antlia, Sextans A and Sextans B appear to form a distinct grouping with kpc relative to the LG, that is located beyond the LG zero-velocity surface at a distance of 1.7 Mpc from the Local Group
centroid. The luminosity distribution of the LG has a slope . This value is significantly less negative than that which is found in rich clusters of galaxies. The luminosity distribution
of the dwarf spheroidal galaxies is steeper than that for dwarf irregulars. Furthermore the dSph galaxies are strongly concentrated
within the Andromeda and Milky Way subclusters of the Local Group, whereas the majority of dIr galaxies appear to be free-floating
members of the LG as a whole. With the possible exception of Leo I and Leo A, most LG members appear to have started forming
stars simultaneously Gyr ago. Many of the galaxies, for which evolutionary data are available, appear to have shrunk with time. This result is
unexpected because Hubble Space Telescope observations appear to show galaxies at to be smaller than they are at . In the Large Magellanic Cloud the rate of cluster formation was low for a period that extended from Gyr to Gyr ago. The rate of cluster formation may have increased more rapidly 3–5 Gyr ago, than did the rate of star formation.
The reason for the sudden burst of cluster formation in the LMC Gyr ago remains obscure. None of the dwarf galaxies in the LG appears to have experienced a starburst strong enough to have
produced a “boojum”.
Received 14 April 1999 相似文献
8.
David D. Meisel Johan Kero Csilla Szasz Vladimir Sidorov Stan Briczinski 《Earth, Moon, and Planets》2008,102(1-4):315-322
In the northern hemisphere, the month of February is characterized by a lack of major meteor shower activity yet a number
of weak minor showers are present as seen by the Kazan radar. Using the Feller transformation to obtain the distribution of
true meteor velocities from the distribution of radial velocities enables the angle of incidence to be obtained for the single
beam AO (Arecibo Observatory) data. Thus the loci of AO radiants become beam-centered circles on the sky and one can, with
simple search routines, find where these circles intersect on radiants determined by other means. Including geocentric velocity
as an additional search criterion, we have examined a set of February radiants obtained at Kazan for coincidence in position
and velocity. Although some may be chance associations, only those events with probabilities of association > 0.5 have been
kept. Roughly 90 of the Kazan showers have been verified in this way with mass, radius and density histograms derived from
the AO results. By comparing these histograms with those of the “background” in which the minor showers are found, a qualitative
scale of dynamical minor shower age can be formulated. Most of the showers are found outside the usual “apex” sporadic source
areas where it is easiest to detect discrete showers with less confusion from the background. 相似文献
9.
Available data on the distances and radial velocities of galaxies are systematized in order to study the distribution of peculiar
velocities in neighborhoods of the Local cosmic void lying in the direction of the Aquila and Hercules constellations. A sample
of 1056 galaxies is used, with distances measured in terms of the luminosity of the tip of the red giant branch (TRGB), the
luminosity of the cepheids, the luminosity of type 1a supernovae, surface brightness fluctuations (SBF), and the Tully-Fisher
relation. The amplitude of the outflow velocity of the galaxies is found to be ∼300 km/s. The average number density of galaxies
inside the void is roughly a factor of five lower than the average outside it. The Local void population is characterized
by lower luminosities and later morphological types, with medians of M
B
= − 15m.7 and T=8 (Sdm), respectively. 相似文献
10.
Results are presented from a detailed spectrophotometric study of a unique system of physically coupled galaxies whose spectra
contain identical emission lines. This system consists of four galaxies, three of which have a double or multiple structure
in their central portions and are, by definition, galaxies with two or multiple nuclei. Two of these objects are the galaxies
with an ultraviolet excess (UVE), Mark 261 and Mark 262, while one is a galaxy made up of two identical starlike nuclei that
are referred to as the “twin objects.” In the DSS2 charts, the latter show up as two adjacent stars without any surroundings.
However, there are two condensations between these starlike nuclei. The fourth object has a triplet structure. It is shown
here that all these objects have the same emission (line) spectra and red shifts. All the physical characteristics that can
be determined from the spectra are determined: red shifts, relative intensities of emission lines, their equivalent widths,
distances to the galaxies, etc. It is concluded that the members of this system have a common origin, more or less consistent
with Ambartsumyan's idea of the fragmentation of an isolated, high density body.
__________
Translated from Astrofizika, Vol. 48, No. 4, pp. 503–514 (November 2005). 相似文献
11.
The HI content of galaxies in the Eridanus group is studied using the GMRT observations and the HIPASS data. A significant
HI deficiency up to a factor of 2–3 is observed in galaxies in the high galaxy density regions. The HI deficiency in galaxies
is observed to be directly correlated to the local projected galaxy density, and inversely correlated to the line-of-sight
radial velocity. Furthermore, galaxies with larger optical diameters are predominantly in the lower galaxy density regions.
It is suggested that the HI deficiency in Eridanus is due to tidal interactions. In some galaxies, evidences of tidal interactions
are seen. An important implication is that significant evolution of galaxies can take place in the group environment. In the
hierarchical way of formation of clusters via mergers of groups, a fraction of the observed HI deficiency in clusters could
have originated in groups. The co-existence of S0s and severely HI deficient galaxies in the Eridanus group suggests that
tidal interaction is likely to be an effective mechanism for transforming spirals to S0s. 相似文献
12.
The initial principles of a method for analyzing the spatial distribution of visible matter in the universe with structures
on size scales of thousands of Mpc are discussed. This method is based on analyzing the distribution N(z) of the photometric
redshifts of galaxies in deep fields using large bins Δ z=0.1–0.3. Fluctuations in the numbers of galaxies in these bins in
terms of redshifts are caused by Poisson noise, correlated structures, and systematic errors in estimating photo-z. This method
involves covering a sufficiently large region of the celestial sphere with a grid of deep multi-band surveys with a cell size
on the order of 10o×10o, with deep fields of size ∼10'×10' observed with 3-10 meter telescopes at its nodes. The distribution
of the photometric redshifts of the galaxies within each deep field will yield information on the radial extent of superlarge
structures, while comparing the radial distributions in neighboring fields will yield information on the tangential extent
of these structures. A necessary element of this method is an analysis of possible distortions in the radial distributions
of the galaxies associated with the technique for evaluating the photometric redshifts. 相似文献
13.
We study the spatial orientation of 5 169 galaxies that have radial velocity 3 000 to 5 000 km s−1. The ‘position angle–inclination’ method is used to find the spin vector and the projections of spin vector of the galaxy
rotation axes. The spatial isotropic distribution is assumed to examine the non-random effects. For this, we have performed
chi-square, Fourier, and auto-correlation tests. We found a random alignment of spin vectors of total galaxies with respect
to the equatorial coordinate system. The spin vector projections of total galaxies is found to be oriented tangentially with
respect to the equatorial center. The spiral galaxies show a similar orientation as shown by the total sample. Five subsamples
of barred spiral (late-type) galaxies show a preferred alignment. However, early-type barred spirals show a random orientation.
A weak morphological dependence is noticed in the subsamples of late type barred spirals. A comparison with the previous works
and the possible explanation of the results will be presented. 相似文献
14.
M. G. Abrahamyan 《Astrophysics》2009,52(1):119-131
The nonlinear dynamics of a rotating jet is examined following its ejection from a compact gravitating object by a vortex
mechanism. A scenario is described in which a dense stream expands and is subsequently transformed into a nonstationary vortex
consisting of a cylindrical core and a “sheath.” At this stage of development, a converging radial flow of matter in the differentially
rotating nonuniform sheath collimates the jet and speeds up the rotation of the core, as well as the flow of matter along
the jet, in accordance with a power law or “explosive” instability, until the velocity discontinuity at the surface of the
core approaches the sound speed. Flows of this type have low energy dissipation and can serve as unique channels for the acceleration
and collimation of jet eruptions from young stars, active galactic nuclei, and quasars.
Translated from Astrofizika, Vol. 52, No. 1, pp. 135–145 (February 2009). 相似文献
15.
We present an analysis of the chiral property of 667 spiral and barred spiral galaxies in the Local Supercluster (radial velocity
<3 000 km s−1). The arms of a galaxy (spiral or barred spiral) can be distinguished according to their orientation (leading or trailing)
relative to the direction of the rotation. We use environment of each galaxy as a subsample in order to study the chiral property
of galaxies. In addition, equatorial position angle distributions of leading and trailing arm galaxies are studied. We classify
our database according as their morphology, diameters, radial velocities, axial ratios and magnitudes. The distribution of
trailing and leading arm galaxies in the Local Supercluster is found homogeneous. A significant dominance of either trailing
or leading structures is noticed within the Virgo cluster region, suggesting that the aggregation of these structures might
have already started there. The rotation axes of the galaxies in the Virgo cluster is found to lie in the equatorial plane.
Chirality of galaxies is found strong for the subsamples that showed a random alignment in the equatorial position angle distribution.
Possible explanations of the results will be presented. 相似文献
16.
E. H. Nikogossyan 《Astrophysics》2001,44(1):23-32
The hierarchical and dynamical structure of the bimodal cluster of galaxies A 548, consisting of the two components A 548E and A 548W, was investigated. An HTree cluster analysis was used for this purpose. Based on the results of the analysis, three main nuclei, five subgroups, and six triplets of galaxies were distinguished in the cluster. These subgroups lie in regions of local density maxima of the entire cluster. The average radial velocities of the subgroups coincide with local maxima in the V
r
distribution of the entire cluster. The members of subgroups are 1.25 stellar magnitudes brighter, on the average, than other galaxies. Based both on the projected positions of the galaxies and on their radial velocities, the field of the cluster has a more uniform structure than does the entire system as a whole. Galaxies with different V
r
are unevenly distributed in the cluster: radial velocity increases from the periphery toward the center. 相似文献
17.
M. G. Abrahamyan 《Astrophysics》2008,51(3):357-371
A vortical mechanism for the collimation and acceleration of astrophysical jets is proposed on the basis of exact solutions
of the hydrodynamic equations in a homogeneous gravitational field taking viscosity into account. Velocity profiles in the
form of a jet structure with a uniformly rotating trunk whose pressure decreases in time, and longitudinal and converging
radial flows of matter, are examined. Because of the radial flow, the angular velocity of the trunk and the velocity of the
longitudinal flow of matter can accelerate exponentially or in the manner of an “explosive” instability. Flows of this type
have low energy dissipation and can serve as unique channels for the acceleration and collimation of jet eruptions from young
stars, as well as from active galactic nuclei and quasars.
__________
Translated from Astrofizika, Vol. 51, No. 3, pp. 431–444 (August 2008). 相似文献
18.
Frank C. van den Bosch Xiaohu Yang H. J. Mo Peder Norberg 《Monthly notices of the Royal Astronomical Society》2005,356(4):1233-1248
Using detailed mock galaxy redshift surveys (MGRSs) we investigate the abundance and radial distribution of satellite galaxies. The mock surveys are constructed using large numerical simulations and the conditional luminosity function (CLF), and are compared against data from the Two Degree Field Galaxy Redshift Survey (2dFGRS). We use Monte Carlo Markov chains to explore the full posterior distribution of the CLF parameter space, and show that the average relation between light and mass is tightly constrained and in excellent agreement with our previous models and with that of Vale & Ostriker. The radial number density distribution of satellite galaxies in the 2dFGRS reveals a pronounced absence of satellites at small projected separations from their host galaxies. This is (at least partly) owing to the overlap and merging of galaxy images in the 2dFGRS parent catalogue. Owing to the resulting close-pair incompleteness we are unfortunately unable to put meaningful constraints on the radial distribution of satellite galaxies; the data are consistent with a radial number density distribution that follows that of the dark matter particles, but we cannot rule out alternatives with a constant number density core. Marginalizing over the full CLF parameter space, we show that in a ΛCDM concordance cosmology the observed abundances of host and satellite galaxies in the 2dFGRS indicate a power spectrum normalization of σ8 ≃ 0.7 . The same cosmology but with σ8 = 0.9 is unable to match simultaneously the abundances of host and satellite galaxies. This confirms our previous conclusions based on the pairwise peculiar velocity dispersions and the group multiplicity function. 相似文献
19.
The distance modulus of the Virgo cluster has been reexamined based on the Tully-Fisher relation between fully corrected B.
1
0
values and 21 cm velocity width derived from RC3 catalogue for spiral galaxies of Sbc-Sdm types, belonging to the “low-velocity”
Virgo subcluster, singled out according to the statistical method proposed by Anosova, and led to the value μ = 31.15 ± 0.57
mag. A strong dependence of the intrinsic scatter in the Tully-Fisher relation on the apparent axes ratio of galaxies has
been found, with a value of 0.4 mag for strongly flattened, highly inclined galaxies and galaxies with small inclinations
and a value of 0.72 mag for objects with intermediate values of axes ratio. The restriction to samples only with galaxies
with photoelectric observations does not lead to a considerable change of amplitude of scatter and decreases the value the
of distance modulus.
Published in Astrofizika, Vol. 42, No. 1, pp. 37–46, January–March, 1999. 相似文献
20.
The linear theory and N-body simulations are used to present a new, alternative model of the galaxy A0035-324 (the “Cartwheel”), which is the most
striking example of the relatively small class of ring galaxies. The model is based on the gravitational Jeans-type instability
of both axisymmetric (radial) and nonaxisymmetric (spiral) small-amplitude gravity perturbations (e.g., those produced by
spontaneous disturbances) of a dynamically cold subsystem (identified as the gaseous component) of an isolated disk galaxy.
The simplified model of a galaxy is used in which stars (and a dark matter, if it exists at all) do not participate in the
disk collective oscillations and just form a background charge. In the theory presented here, a case for both purely radial
solutions and purely spiral solutions to the equations of motion of an infinitesimally thin gaseous disk is made, which is
associated with both a radial density wave and a dominant spiral density wave which propagate outwards creating a rough ring
and a number of spiral arms. Through three-dimensional numerical simulation of a collisionless set of many particles, I associate
these gravitationally unstable axisymmetric waves and nonaxisymmetric waves with growing clumps of matter which take on the
appearance of a ring and spokes of mass blobs. 相似文献