共查询到20条相似文献,搜索用时 15 毫秒
1.
Kenji Bekki 《Astrophysics and Space Science》2001,276(2-4):1033-1036
A significant fraction of clusters of galaxies are observed to have substructure, which implies that merging between clusters
and subclusters is a rather common physical process in cluster formation. It still remains unclear how cluster merging affects
the evolution of cluster member galaxies. We report the results of numerical simulations that show the dynamical evolution
of a gas-rich, late-type spiral in a merger between a small group of galaxies and a cluster. The simulations demonstrate that
the time-dependent tidal gravitational field during merging excites non-axisymmetric structure of the galaxy, subsequently
drives efficient transfer of gas to the central region and finally triggers a secondary starburst. This result provides a
close physical relationship between the emergence of starburst galaxies and the formation of substructure in clusters. We
accordingly interpret post-starburst galaxies located near substructure of the Coma Cluster as one observational example indicating
the global tidal effects of group–cluster merging. Our numerical results further suggest a causal link between the observed
excess of blue galaxies in distant clusters and the cluster virialization process through hierarchical merging of subclusters.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Christopher J. Conselice & John S. Gallagher III 《Monthly notices of the Royal Astronomical Society》1998,297(2):L34-L38
We present evidence for a new morphologically defined form of small-scale substructure in the Coma cluster, which we call galaxy aggregates. Aggregates are dominated by a central galaxy, which is on average 5 mag brighter than the smaller aggregate members, nearly all of which lie to one side of the central galaxy. We have found three such galaxy aggregates: two dominated by the S0 galaxies RB 55 and RB 60, and one by the starbursting SBb NGC 4858. RB 55 and 60 are both equidistant between the two dominant D galaxies NGC 4874 and 4889, while NGC 4858 is located near the large E0 galaxy NGC 4860. All three central galaxies have redshifts consistent with Coma cluster membership. We describe the spatial structures of these unique objects, and suggest several possible mechanisms to explain their origin. These include: chance superpositions from background galaxies, interactions between other galaxies and with the cluster gravitational potential, and ram pressure. We conclude that the most probable scenario of creation is an interaction with the cluster through its gravitational potential. 相似文献
3.
We have observed the region of the Coma cluster at 34.5 MHz with a resolution of 26 arcmin × 40 arcmin. A map of the diffuse
halo (Coma C) is presented. The size of the halo is found to be 54 arcmin × 30 arcmin. The position angle is 50° ± 10° and
the integrated flux is 60 ± 11 Jy.
We have also found an extended source to the south of Coma A. The measured half-power widths of this source are 30 arcmin
× 40 arcmin. The position angle is 135° and the integrated flux is ~ 15 Jy at 34.5 MHz. The spectral index in the frequency
range 408 to 34.5 MHz is -1.0. It is suggested that this source also belongs to the Coma cluster. 相似文献
4.
对于星系际弥散恒星的研究是分别从观测、数值模拟和半解析模型这三个方面进行的.现在已经在邻近星系团及中低红移处观测到弥散恒星,甚至在Virgo及Coma星系团中观测到了单个的弥散恒星.观测数据的积累使得人们能够从统计上了解星系际弥散恒星的性质.研究表明星系际弥散恒星围绕着星系团势阱中心呈椭球状对称分布,其在星系团恒星总质... 相似文献
5.
Noah Brosch Eran O. Ofek Elhanan Almoznino Timothy Sasseen Michael Lampton & Stuart Bowyer 《Monthly notices of the Royal Astronomical Society》1998,295(4):959-969
We analyse an ultraviolet observation toward the Coma cluster by means of the FAUST shuttle-borne telescope. We detect 56 candidate sources to a signal-to-noise ratio of 6.5. Most sources have optical counterparts in existing catalogues and are stars. 10 sources with no listed counterparts were observed at the Wise Observatory. We present identifications based on low-resolution spectrophotometry, and discuss the foreground stars and the galaxies, all in the foreground of the Coma cluster. The FAUST image yields a higher fraction of hot evolved stars than either of the North Galactic Pole or the Virgo regions, analysed previously. We identify these tentatively as cooling white dwarfs in the Coma Berenices (Mel 111) open cluster. 相似文献
6.
This paper deals with the observed variation in the flattening of galaxies with the density of galaxies in the subclusters
of Coma surrounding NGC 4889, NGC 4874, and NGC 4839 based on data from the Abastumani Combined Catalog of Galaxies. The mean
values of the observed ratios of the diameters of the galaxies, as well as histograms of their distributions, indicate that
in the central, dense regions of the subclusters within a volume of 0.5h
75
−1
Mpc3, E and S0 type galaxies are close to spheroidal. A significant reduction in the mean values of the diameters of the galaxies
in the subclusters is noted, regardless of their morphology relative to the galaxies in the halo of the Coma cluster. In the
subclusters, spiral galaxies are found with a hydrogen deficit that is more than 5 times the hydrogen deficit in spirals within
the halo of the cluster. According to their 3-D coordinates, most of the galaxies with a hydrogen deficit are located closer
to the south-east edge of the subcluster surrounding NGC 4874 near an extended gas filament in the x-ray region. This may
indicate that the subcluster is moving toward a central condensation of faint galaxies in the Coma cluster and a possible
merger with it.
__________
Translated from Astrofizika, Vol. 50, No. 3, pp. 355–368 (August 2007). 相似文献
7.
A photographic photometry in U was performed for 288 galaxies in the central field of the Coma cluster of galaxies. 相似文献
8.
F. W. Baier 《Astronomische Nachrichten》1984,305(4):175-185
The investigation of the distributions of number densities and radial velocities in the Coma cluster led us to the conclusion that this cluster possesses substructures. This result is in agreement with corresponding results for the Hydra I cluster and the Perseus cluster and with former conclusions by different authors that substructures are a typical phenomenon for a high percentage of all clusters of galaxies. 相似文献
9.
A. Pagliaro V. Antonuccio-Delogu U. Becciani M. Gambera 《Monthly notices of the Royal Astronomical Society》1999,310(3):835-841
We present and discuss a method to identify substructures in combined angular-redshift samples of galaxies within clusters. The method relies on the use of the discrete wavelet transform (hereafter DWT) and has already been applied to the analysis of the Coma cluster. The main new ingredient of our method with respect to previous studies lies in the fact that we make use of a 3D data set rather than a 2D one. We test the method on mock cluster catalogues with spatially localized substructures and on a N -body simulation. Our main conclusion is that our method is able to identify the existing substructures provided that: (a) the subclumps are detached in part or all of the phase space, (b) one has a statistically significant number of redshifts, increasing as the distance decreases due to redshift distortions; (c) one knows a priori the scale on which substructures are to be expected. We have found that to allow an accurate recovery we must have both a significant number of galaxies (≈200 for clusters at z ≥0.4 or about 800 at z ≤0.4) and a limiting magnitude for completeness m B =16.
The only true limitation to our method seems to be the necessity of knowing a priori the scale on which the substructure is to be found. This is an intrinsic drawback of the method and no improvement in numerical codes based on this technique could make up for it. 相似文献
The only true limitation to our method seems to be the necessity of knowing a priori the scale on which the substructure is to be found. This is an intrinsic drawback of the method and no improvement in numerical codes based on this technique could make up for it. 相似文献
10.
We study how the internal structure of dark halos is affected if cold dark matter particles are assumed to have a large cross section for elastic collisions. We identify a cluster halo in a large cosmological N-body simulation and resimulate its formation with progressively increasing resolution. We compare the structure found in the two cases in which dark matter is treated as collisionless or as a fluid. For the collisionless case, the overall ellipticity of the cluster, the central density cusp, and the amount of surviving substructure are all similar to those found in earlier high-resolution simulations. Collisional dark matter results in a cluster that is more nearly spherical at all radii, has a steeper central density cusp, and has less-but still substantial-surviving substructure. As in the collisionless case, these results for a "fluid" cluster halo are expected to carry over approximately to smaller mass systems. The observed rotation curves of dwarf galaxies then argue that self-interacting dark matter can only be viable if intermediate cross sections produce structure that does not lie between the extremes we have simulated. 相似文献
11.
J. Donnert K. Dolag G. Brunetti R. Cassano A. Bonafede 《Monthly notices of the Royal Astronomical Society》2010,401(1):47-54
We use the results from a constrained, cosmological magnetohydrodynamic simulation of the Local Universe to predict the radio halo and the γ-ray flux from the Coma cluster and compare it to current observations. The simulated magnetic field within the Coma cluster is the result of turbulent amplification of the magnetic field during the build-up of the cluster. The magnetic seed field originates from starburst driven, galactic outflows. The synchrotron emission is calculated assuming a hadronic model. We follow four approaches with different distributions for the cosmic ray proton population within galaxy clusters. The radial profile of the radio halo can only be reproduced with a radially increasing energy fraction within the cosmic ray proton population, reaching >100 per cent of the thermal-energy content at ≈1 Mpc, for example the edge of the radio-emitting region. Additionally, the spectral steepening of the observed radio halo in Coma cannot be reproduced, even when accounting for the negative flux from the thermal Sunyaev–Zeldovich effect at high frequencies. Therefore, the hadronic models are disfavoured from the present analysis. The emission of γ-rays expected from our simulated Coma is still below the current observational limits (by a factor of ∼6) but would be detectable by FERMI observations in the near future. 相似文献
12.
Six subclusters in the Coma cluster have been selected on the basis of a hierarchical clustering method that takes the gravitational
interaction among galaxies into account. Of these, 3 central subclusters around the galaxies NGC 4889, NGC 4874, and NGC 4839
have been singled out. We have used the objective statistical criterion applied by Vennik and Anosova in studies of close
groups of galaxies to evaluate each member included in a subcluster with a high probability. Galaxies with a significant deficit
of hydrogen HI, including objects from the Bravo-Alfaro list, have been identified with members of the subclusters, with the
greatest number of them in the subclusters around NGC 4874 and NGC 4839. A quantitative estimate of the hydrogen deficit using
the HI index in the RCG3 catalog reveals a statistically significant excess value for those galaxies that are members of the
subclusters compared to galaxies with a hydrogen deficit in the overall Coma cluster field. A substantial number of the spiral
galaxies with a hydrogen deficit in the subclusters turned out to be radio galaxies as well.
__________
Translated from Astrofizika, Vol. 48, No. 4, pp. 515–528 (November 2005). 相似文献
13.
K. Rudnicki 《Astronomische Nachrichten》1976,297(6):317-322
A morphological box for the space distribution of galaxies and dark matter as the consequence of various types of cosmogonical hypotheses is presented. A short review of concepts of clustering of galaxies is given. One has to distinguish between the phenomena of “clusters of galaxies” and of “clustering of galaxies”. The second notion is more general. The investigations of KIANG , FLIN , and PEEBLES speak in favour of general clustering rather than overal existence of individual clusters. Individuals such as our Supergalaxy, Coma cluster etc. seem rather to be exceptional features. 相似文献
14.
T. Kodama 《Astrophysics and Space Science》2001,276(2-4):877-884
The colour-magnitude relation provides important information on the formation and evolution of cluster galaxies. By looking
into the evolution of the relation as a function of redshift and using the small colour scatter around the relation in Coma,
we put constraints on the star formation history and the galaxy merging history of cluster early-type galaxies.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
Coma闭是离我们最近的典型富星系闭之一。对此,人们积累了丰富的观测资料,并且进行了广泛深入的研究。在本文中着重介绍了有关Coma闭的成员判定、结构、光度函数、动力学和次结构等方面的研究情况,并简单介绍了目前的最新研究动态。 相似文献
16.
Inger Jørgensen & Helge Jønch-Sørensen 《Monthly notices of the Royal Astronomical Society》1998,297(3):968-976
We have studied the poor southern cluster of galaxies S639. Based on new Strömgren photometry of stars in the direction of the cluster, we confirm that the Galactic extinction affecting the cluster is large. We find the extinction in Johnson B to be AB =0.75±0.03. We have obtained new photometry in Gunn r for E and S0 galaxies in the cluster. If the Fundamental Plane is used for determination of the relative distance and the peculiar velocity of the cluster, we find a distance, in velocity units, of (5706±350) km s−1 , and a substantial peculiar velocity, (839±350) km s−1 . However, the colours and the absorption line indices of the E and S0 galaxies indicate that the stellar populations in these galaxies are different from those in similar galaxies in the two rich clusters Coma and Hydra I. This difference may severely affect the distance determination and the derived peculiar velocity. The data are consistent with a non-significant peculiar velocity for S639 and the galaxies in the cluster being on average 0.2 dex younger than similar galaxies in Coma and Hydra I. The results for S639 caution that some large peculiar velocities may be spurious and caused by unusual stellar populations. 相似文献
17.
D. Calzetti J. Einasto M. Giavalisco R. Ruffini E. Saar 《Astrophysics and Space Science》1987,137(1):101-106
The observational data on the amplitude of the correlation function of galaxies in the direction of the Coma cluster are confronted with an analytic formula derived for a self-similar observer-homogeneous structure. 相似文献
18.
Neil Trentham 《Monthly notices of the Royal Astronomical Society》1998,293(1):71-88
We present the luminosity function and measurements of the scalelengths, colours and radial distribution of dwarf galaxies in the Coma cluster down to R =24. Our survey area is 674 arcmin2 ; this is the deepest and most detailed survey covering such a large area.
Our measurements agree with those of most previous authors at bright and intermediate magnitudes. The new results are as follows.
(1) Galaxies in the Coma cluster have a luminosity function φ( L )∝ Lα that is steep (α∼−1.7) for −15< MR <−11, and is shallower brighter than this. The curvature in the luminosity function at MR ∼−15 is statistically significant.
(2) The galaxies that contribute most strongly to the luminosity function at −14< MR <−12 have colours and scalelengths that are consistent with those of local dwarf spheroidal galaxies placed at the distance of Coma.
(3) These galaxies with −14< MR <−12 have a colour distribution that is very strongly peaked at B − R =1.3. This is suggestive of a substantial degree of homogeneity in their star formation histories and metallicities.
(4) These galaxies with −14< MR <−12 also appear to be more confined to the cluster core ( r ∼200 kpc) than the brighter galaxies. Alternatively, this observation may be explained in part or whole by the presence of an anomalously high number of background galaxies behind the cluster core. Velocity measurements of these galaxies would distinguish between these two possibilities. 相似文献
Our measurements agree with those of most previous authors at bright and intermediate magnitudes. The new results are as follows.
(1) Galaxies in the Coma cluster have a luminosity function φ( L )∝ L
(2) The galaxies that contribute most strongly to the luminosity function at −14< M
(3) These galaxies with −14< M
(4) These galaxies with −14< M
19.
Neil Trentham & Bahram Mobasher 《Monthly notices of the Royal Astronomical Society》1998,293(1):53-59
We present the discovery of a giant low-surface-brightness arc, of length ∼80 kpc, in the Coma cluster. The arc consists of a diffuse luminous matrix with surface brightness μB <26.5 mag arcsec−2 and a number of embedded condensations. It is not associated with any giant galaxy in Coma in particular; neither does it have the properties of a gravitational arc. We argue that a fast interaction between the nearby barred S0 galaxy IC 4026 and either IC 4041 or RB 110 is the most natural explanation for the origin of the arc. 相似文献
20.
Photographic magnitudes in the UBV system of 39 stars in the Coma cluster of galaxies are given. 相似文献