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1.
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
2.
We present an analysis of the orientations of 1433 galaxies found in the region 15h 48m ≤α(2000) ≤ 19h 28m , −68°≤δ(2000) ≤−62° . In this region we investigated three Abell clusters (S0794, S0797, S0805) of richness Class 0 and the Triangulum Australis cluster. Our aim is to examine non-random effects in galaxy orientations in clusters. In addition, we classified the investigated galaxies into subsamples on the basis of their axial ratio, major diameter and morphology. The spin vector orientations of total galaxies in the investigated region is found to be random. No preferred orientation is found in the clusters. We could not note any morphological dependence of the galaxy orientations in our samples. No preferred orientations can be seen for the spiral galaxies. The morphologically unidentified galaxies, galaxies having major diameters of <47 arcsec, and the nearly edge-on galaxies ( b / a < 0.5, 0.4 < b / a ≤ 0.5) show anisotropy: spin vectors of galaxies tend to be oriented perpendicular to the Local Supercluster plane and spin vector projections tend to point radially with respect to the Virgo cluster centre. 相似文献
3.
Gene G. Byrd M. Thomasson K. J. Donner B. Sundelius T. Y. Huang M. J. Valtonen 《Celestial Mechanics and Dynamical Astronomy》1988,45(1-3):31-36
We study, theoretically and with N-body simulations, the formation of spiral patterns in retrograde galaxy encounters. A one-armed leading spiral dominates in a disk if the tidal perturbation from the companion is large and the disk is surrounded by a massive halo. Otherwise, a trailing pattern forms. The leading arm is made up of particles in slightly elongated orbits whose turning points outline the arm. The arm rotates opposite to the disk rotation. We have found one spiral galaxy, NGC4622, with a leading arm near its nucleus. From the literature, we find that very few spirals, if any, in a sample of strongly perturbed galaxies have leading arms. A possible reason for this is that few spiral galaxies have a halo with larger mass than the disk within the visible disk. 相似文献
4.
Distributions of the surface brightness and the surface color of five barred spiral galaxies expressed in the form of digital maps are presented. This is the first step to determine the composition of the components of barred spiral galaxies — bar, spiral arm, inner ring and outer ring — and to obtain an accurate picture of the dynamical model of a barred spiral galaxy. We have found that (a) the bar is redder than the spiral arm and has a color similar to that of the disk and (b) the inner ring of theSB(r) type galaxy is bluer than the bar and rather resembles the spiral arm. 相似文献
5.
为了避开旧物质臂理论中旋臂的缠绕困难，本文提出了旋涡星系的循环假设，并在文中提供了旋涡星系的双臂、气体层反卷、银河系中旋臂物质径向向内的速度分量和棒旋星系中棒物质沿着棒向内的流动等观测证据，进而还尝试利用此循环假设去解释旋臂物质的平自转曲线和棒旋星系的棒结构等的成因。 相似文献
6.
We investigate the distribution and velocity field of galaxies situated in a band of 100 by 20 degrees centered on M87 and oriented along the Local supercluster plane. Our sample amounts 2158 galaxies with radial velocities less than 2000 km s?1. Of them, 1119 galaxies (52%) have distance and peculiar velocity estimates. About 3/4 of early-type galaxies are concentrated within the Virgo cluster core, most of the late-type galaxies in the band locate outside the virial radius. Distribution of gas-rich dwarfs with MHI >M* looks to be insensitive to the Virgo cluster presence. Among 50 galaxy groups in the equatorial supercluster band 6 groups have peculiar velocities about 500–1000 km s?1 comparable with virial motions in rich clusters. The most cryptic case is a flock of nearly 30 galaxies around NGC4278 (Coma I cloud), moving to us with the mean peculiar velocity of ?840 km s?1. This cloud (or filament?) resides at a distance of 16.1 Mpc from us and approximately 5 Mpc away from the Virgo center. Galaxies around Virgo cluster exhibit Virgocentric infall with an amplitude of about 500 km s?1. Assuming the spherically symmetric radial infall, we estimate the radius of the zero-velocity surface to be R0 = (7.0±0.3) Mpc that yields the total mass of Virgo cluster to be (7.4 ± 0.9)× 1014M⊙ in tight agreement with its virial mass estimates. We conclude that the Virgo outskirts does not contain significant amounts of dark mater beyond its virial core. 相似文献
7.
F. X. Hu G. X. Wu G. X. Song Q. R. Yuan S. Okamura 《Astrophysics and Space Science》2006,302(1-4):43-59
The progress of the studies on the orientation of galaxies in the Local Supercluster (LSC) is reviewed and a summary of recent
results is given. Following a brief introduction of the LSC, we describe the results of early studies based on two-dimensional
analysis, which were mostly not conclusive. We describe next the three-dimensional analysis, which is used widely today. Difficulties
and systematic effects are explained and the importance of selection effects is described. Then, results based on the new
method and modern databases are given, which are summarized as follows. When the LSC is seen as a whole, galaxy planes tend
to align perpendicular to the LSC plane with lenticulars showing the most pronounced tendency. Projections onto the LSC plane
of the spin vectors of Virgo cluster member galaxies, and to some extent, those of the total LSC galaxies, tend to point to
the Virgo cluster center. This tendency is more pronounced for lenticulars than for spirals. It is suggested that ‘field’
galaxies, i.e., those which do not belong to groups with more than three members, may be better objects than other galaxies
to probe the information at the early epoch of the LSC formation through the analysis of galaxy orientations. Field lenticulars
show a pronounced anisotropic distribution of spin vectors in the sense that they lay their spin vectors parallel to the LSC
plane while field spirals show an isotropic spin-vector distribution. 相似文献
8.
We present an analysis of the spatial orientations of 1315 galaxies in 10 Abell clusters of BM type II–III (type II–III in the Bautz–Morgan system). It is found that the spin-vector orientations of the galaxies in six clusters (Abell 168, 426, 1035, 1227, 1367 and 1904) tend to lie parallel to the Local Supercluster (LSC) plane. The spin-vector projections of galaxies in six clusters (Abell 168, 1020, 1035, 1227, 1904 and 1920) are found to be oriented perpendicular with respect to the direction of the LSC centre. Three clusters (Abell 1920, 2255 and 2256) show a bimodal orientation: spin vectors tend to be oriented both parallel and perpendicular to the LSC plane. No dependence of radial velocity, distance and cluster magnitude on galaxy orientation is noticed. In a comparison with previous work, we noticed that the anisotropy might increase from early-type (BM type I) to late-type (BM types II–III and III) clusters. We notice a vanishing angular momentum for the less massive galaxy clusters (richness class 0). A significant alignment of the angular momenta of galaxies for massive clusters, e.g. the core of the Shapley Supercluster (richness class 4, M > 1015 M⊙ ), is found. 相似文献
9.
By using the SDSS spectra, we have studied the star formation properties of the nearby spiral galaxies selected from the Revised Bright Galaxy Sample, and tried to find the effect of bar structure on the star formation activity in the nuclear regions of nearby galaxies. The stellar population composition and the intensity of star formation activities of each sample galaxy are acquired by using the stellar population synthesis code—STARLIGHT, and the star formation properties of nuclear regions are compared with those of integral sample galaxies. We find that the star formation in barred spiral galaxies is more active than that of unbarred spirals, and that barred spirals have younger stellar populations. 相似文献
10.
The apparatus of a correlation gamma function is used to analyze the spatial clustering of galaxies in the Local Supercluster. In particular, we analyzed a sample corrected for the peculiar velocities of the Local Supercluster galaxies by using our original technique for separating groups of galaxies. It turned out that the peculiar velocities did not significantly distort the gamma function even for relatively small sample sizes. The distribution of the galaxies obeys a power-law decrease in density with an index of 0.6–0.7. We found evidence for a luminosity dependence of the degree of galaxy clustering within the volume under study. 相似文献
11.
D. Pérez-Ramírez J. H. Knapen † R. F. Peletier S. Laine R. Doyon † D. Nadeau † 《Monthly notices of the Royal Astronomical Society》2000,317(2):234-248
We present subarcsecond-resolution, ground-based, near-infrared images of the central regions of a sample of 12 barred galaxies with circumnuclear star formation activity, which is organized in ring-like regions typically 1 kpc in diameter. We also present Hubble Space Telescope near-infrared images of 10 of our sample galaxies, and compare them with our ground-based data. Although our sample galaxies were selected for the presence of circumnuclear star formation activity, our broad-band near-infrared images are heterogeneous, showing a substantial amount of small-scale structure in some galaxies, and practically none in others. We argue that, where it exists, this structure is caused by young stars, which also cause the characteristic bumps or changes in slope in the radial profiles of ellipticity, major axis position angle, surface brightness and colour at the radius of the circumnuclear ring in most of our sample galaxies. In seven out of 10 HST images, star formation in the nuclear ring is clearly visible as a large number of small emitting regions, organized into spiral arm fragments, which are accompanied by dust lanes. Near-infrared colour index maps show much more clearly the location of dust lanes and, in certain cases, regions of star formation than single broad-band images. Circumnuclear spiral structure thus outlined appears to be common in barred spiral galaxies with circumnuclear star formation. 相似文献
12.
We examine a sample of 65 galaxies in the Virgo cluster with negative radial velocities relative to the Local Group. Some
features of this sample are pointed out. All of these objects are positioned compactly within a virial zone of radius 6o in
the cluster, but their centroid is displaced relative to the dynamic center of the cluster, M87, by 1o.1 to the northwest.
The dwarf galaxies in this sample are clumped on a scale of ∼10' (50 kpc). The observed asymmetry in the distribution of the
blueshifted galaxies may be caused by infall of a group of galaxies around M86 onto the main body of the cluster. We offer
another attempt to explain this phenomenon, assuming a mutual tangential velocity of ∼300 km/s-1 between the Local Group and the Virgo cluster owing to their being repelled from the local cosmological void. 相似文献
13.
The Milky Way is a spiral galaxy with (or without) a bar-like central structure. There is evidence that the distribution of suspected cosmic ray sources, such as supernova remnants, are associated with the spiral arm structure of galaxies. It is yet not clearly understood what effect such a cosmic ray source distribution has on the particle transport in our Galaxy. We investigate and measure how the propagation of Galactic cosmic rays is affected by a cosmic ray source distribution associated with spiral arm structures.We use the PICARD code to perform high-resolution 3D simulations of electrons and protons in galactic propagation scenarios that include four-arm and two-arm logarithmic spiral cosmic ray source distributions with and without a central bar structure as well as the spiral arm configuration of the NE2001 model for the distribution of free electrons in the Milky Way. Results of these simulation are compared to an axisymmetric radial source distribution. Also, effects on the cosmic ray flux and spectra due to different positions of the Earth relative to the spiral structure are studied.We find that high energy electrons are strongly confined to their sources and the obtained spectra largely depend on the Earth’s position relative to the spiral arms. Similar finding have been obtained for low energy protons and electrons albeit at smaller magnitude. We find that even fractional contributions of a spiral arm component to the total cosmic ray source distribution influences the spectra on the Earth. This is apparent when compared to an axisymmetric radial source distribution as well as with respect to the Earth’s position relative to the spiral arm structure. We demonstrate that the presence of a Galactic bar manifests itself as an overall excess of low energy electrons at the Earth.Using a spiral arm geometry as a cosmic ray source distributions offers a genuine new quality of modeling and is used to explain features in cosmic ray spectra at the Earth that are else-wise attributed to other propagation effects. We show that realistic cosmic ray propagation scenarios have to acknowledge non-axisymmetric source distributions. 相似文献
14.
15.
J. I. Davies S. Roberts S. Sabatini 《Monthly notices of the Royal Astronomical Society》2005,356(2):794-800
Galaxy harassment has been proposed as a physical process that morphologically transforms low surface density disc galaxies into dwarf elliptical galaxies in clusters. It has been used to link the observed very different morphology of distant cluster galaxies (relatively more blue galaxies with 'disturbed' morphologies) with the relatively large numbers of dwarf elliptical galaxies found in nearby clusters. One prediction of the harassment model is that the remnant galaxies should lie on low surface brightness tidal streams or arcs. We demonstrate in this paper that we have an analysis method that is sensitive to the detection of arcs down to a surface brightness of 29 B μ and we then use this method to search for arcs around 46 Virgo cluster dwarf elliptical galaxies. We find no evidence for tidal streams or arcs and consequently no evidence for galaxy harassment as a viable explanation for the relatively large numbers of dwarf galaxies found in the Virgo cluster. 相似文献
16.
M. S. Seigar D. L. Block I. Puerari N. E. Chorney P. A. James 《Monthly notices of the Royal Astronomical Society》2005,359(3):1065-1076
In the last decade, near-infrared imaging has highlighted the decoupling of gaseous and old stellar discs: the morphologies of optical (Population I) tracers compared to the old stellar disc morphology, can be radically different. Galaxies which appear multi-armed and even flocculent in the optical may show significant grand-design spirals in the near-infrared. Furthermore, the optically determined Hubble classification scheme does not provide a sound way of classifying dust-penetrated stellar discs: spiral arm pitch angles (when measured in the near-infrared) do not correlate with Hubble type. The dust-penetrated classification scheme of Block & Puerari provides an alternative classification based on near-infrared morphology, which is thus more closely linked to the dominant stellar mass component. Here we present near-infrared K -band images of 14 galaxies, on which we have performed a Fourier analysis of the spiral structure in order to determine their near-infrared pitch angles and dust-penetrated arm classes. We have also used the rotation curve data of Mathewson et al. to calculate the rates of shear in the stellar discs of these galaxies. We find a correlation between near-infrared pitch angle and rate of shear: galaxies with wide open arms (the γ class) are found to have rising rotation curves, while those with falling rotation curves belong to the tightly wound α bin. The major determinant of near-infrared spiral arm pitch angle is the distribution of matter within the galaxy concerned. The correlation reported in this study provides the physical basis underpinning spiral arm classes in the dust-penetrated regime and underscores earlier spectroscopic findings by Burstein and Rubin that Hubble type and mass distributions are unrelated. 相似文献
17.
M. Viel E. Branchini R. Cen J. P. Ostriker S. Matarrese P. Mazzotta B. Tully 《Monthly notices of the Royal Astronomical Society》2005,360(3):1110-1122
We present a simple method for tracing the spatial distribution and predicting the physical properties of the Warm–Hot Intergalactic Medium (WHIM), from the map of galaxy light in the Local Universe. Under the assumption that biasing is local and monotonic we map the ∼2 h −1 Mpc smoothed density field of galaxy light into the mass-density field, from which we infer the spatial distribution of the WHIM in the Local Supercluster. Taking into account the scatter in the WHIM density–temperature and density–metallicity relation, extracted from the z = 0 outputs of high-resolution and large-box-size hydrodynamical cosmological simulations, we are able to quantify the probability of detecting WHIM signatures in the form of absorption features in the X-ray spectra, along arbitrary directions in the sky. To illustrate the usefulness of this semi-analytical method we focus on the WHIM properties in the Virgo cluster region. 相似文献
18.
A.M. Fridman O.V. Khoruzhii V.V. Lyakhovich V.S. Avedisova O.K. Sil'chenko A.V. Zasov A.S. Rastorguev V.L. Afanas'iev S.N. Dodonov J. Boulesteix 《Astrophysics and Space Science》1997,252(1-2):115-131
General ideas, as well as experimental and theoretical efforts concerning the prediction and discovery of new structures in the disks of spiral galaxies – giant anticyclones - are reviewed. A crucial point is the development of a new method to restore the full vector velocity field of the galactic gas from the line-of-sight velocity field. This method can be used to get self-consistent solutions for the following problems: 1) determination of non-circular velocities associated with spiral-vortex structure; 2) determination of fundamental parameters of this structure: pattern speed, corotation radius, location of giant anticyclones; 3) refinement of galactic rotation curves taking into account regular non-circular motion in the spiral density wave, which makes it possible to build more accurate models of the mass distribution in the galaxy; 4) refinement of parameters of the rotating gaseous disk: inclination angle, center of rotation and position angle of the major dynamical axis, systematic velocity. The method is demonstrated using the restoration of the velocity field of the galaxy NGC 157 as an example. Results for this and some other spiral galaxies suggest that giant anticyclones are a universal property of galaxies with grand design structure. 相似文献
19.
F. W. Baier 《Astronomische Nachrichten》1980,301(1):17-26
The number density distribution of galaxies in the region of the UMa Supercluster of galaxies was derived by counting galaxies on the red Palomar Sky Survey prints. For fourteen clusters in this region the radial number density distribution and the radial cumulative galaxy distribution were calculated. 相似文献
20.
The widely varying dwarf galaxy counts in different environments provide a strong challenge to standard hierarchical clustering
models. The luminosity function is not universal, but seems to be strongly dependent upon environment. In this paper we describe
an automated procedure for detecting and measuring very Low Surface Brightness (LSB) features in deep CCD data. We apply this
procedure to large area CCD survey fields of the Virgo cluster and find 105 dwarf LSB galaxies previously uncatalogued over
an area of ∼14 sq deg. We show that there are many more faint (14≤MB≤–10) LSB galaxies than would be predicted from extrapolation of the Virgo cluster catalogue luminosity function. Over our
limited range of measurement the faint end slope of the luminosity function becomesα=–1.6. Although these galaxies contribute
a small fraction of the total stellar light of the cluster, they may contribute significantly to the mass in galaxies if they
have large mass-to-light ratios similar to those recently measured for Local Group dwarf galaxies. By a comparison with different
environments, the Virgo Cluster seems to be highly `dwarf rich' if considering the dwarf to giant ratio or it's luminosity
function faint end slope.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献