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Topic: Groups and clusters of galaxies


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In the News (Thu 23 Nov 17)

  
  Groups and clusters of galaxies - Wikipedia, the free encyclopedia
Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos.
Groups of galaxies are the smallest aggregates of galaxies.
Note: clusters of galaxies should not be confused with star clusters such as galactic clusters and open clusters, which are structures within galaxies, as well as globular clusters, which typically orbit galaxies.
en.wikipedia.org /wiki/Groups_and_clusters_of_galaxies   (796 words)

  
 OaTs-HomePage Osservatorio Astronomico di Trieste
The analysis of galaxy systems therefore concerns several aspects of the extragalactic astronomy: the mass content of the Universe and the formation and evolution of large scale structures, the evolution of the galaxies members of groups and clusters, and the interplay between these galaxies and the intracluster diffuse hot gas.
remnants of groups gravitationally accreted by the cluster.
In fact, clusters are characterized by their high mass density and by the presence of a very hot diffuse gas, and both can significantly affect the properties of cluster galaxies.
www.ts.astro.it /astro/laricerca_extgal_2enil.html   (1356 words)

  
 The XMM Newton Satellite Schoolpage
Many galaxies are clumped together into small groups or larger clusters of galaxies which are bound together by gravitational force.
However the group is in the process of collapsing, and in a few billion years our galaxy is likely to interact with M31, and may eventually merge with it.
In groups the brightness of this gas is lower than in clusters, and one can see that X-rays are also being radiated from some of the galaxies, especially the ellipticals, which are usually brighter X-ray sources than the spirals.
www.sr.bham.ac.uk /xmm/cluster.html   (794 words)

  
 Groups of Galaxies   (Site not responding. Last check: 2007-10-07)
In discussions of galaxy groupings, it is useful to introduce two technical terms: The velocity dispersion measures the spread in velocities for the members of the group of galaxies.
We find that the galaxies themselves form into groups and clusters of galaxies held together by mutual gravitational attraction, that clusters of galaxies are themselves associated with even larger superclusters of galaxies that are bound gravitationally, and that there may be even larger structures that correlate groups of superclusters.
The total mass contained in a group is of order 10 trillion solar masses, which is several times the mass of the Milky Way, and the velocity dispersion (that is, the range of velocities for individual members of the group, see the adjacent box) is typically about 150 km/s or less.
csep10.phys.utk.edu /ojta/course2/galaxies/clusters/groups_tl.html   (424 words)

  
 Nat' Academies Press, (NAS Colloquium) The Age of the Universe, Dark Matter, and Structure Formation (1998)
X-ray emissions from clusters and groups of galaxies, pp.
X-ray emission from clusters and groups of galaxies
Clusters as Cosmological Probes Clusters are thought to be “fair samples” of the universe, i.e., they represent such a large perturbation (≈10 Mpc comoving volume) that their content should be representative of the universe as a whole.
books.nap.edu /books/0309060265/html/72.html   (5849 words)

  
 Chandra :: Field Guide to X-ray Sources :: Groups & Clusters of Galaxies
Although the galaxies and hot gas clouds are very massive, scientists have determined that about 10 times more mass is needed to hold the cluster together.
Astronomers think that galaxy clusters form as clumps of dark matter and their associated galaxies are pulled together by gravity to form groups of dozens of galaxies, which in turn merge to form clusters of hundreds, even thousands of galaxies.
This heating can be a violent process as gas clouds enveloping groups of galaxies collide and merge to become a cluster over billions of years.
chandra.harvard.edu /xray_sources/galaxy_clusters.html   (257 words)

  
 Galaxy Clusters
Galaxies are preferentially found in groups or larger agglomerations called clusters.
Virgo, an irregular cluster, is the nearest large cluster of galaxies.
Galaxy positions are plotted as white points and large filamentary and sheet-like structures are evident, as well as bubble-like voids (CfA).
www.damtp.cam.ac.uk /user/gr/public/gal_lss.html   (562 words)

  
 Globular Clusters and Dwarf Galaxies
The keys seem to lie within clusters of galaxies, where ellipticals, spirals, and irregulars are found; interactions between galaxies have surely played an important role in their evolutive histories.
Globular Clusters (GC) and Dwarf Galaxies (DG) are the simplest and most numerous stellar systems that populate these environments, hence their importance is fundamental for tracing the dynamical and chemical evolution that galaxies underwent along the whole age of the Universe.
On the other hand, being by far the most numerous type of galaxy within groups and clusters of galaxies, dwarfs are main characters in the interactions, captures, and mergers that, we believe, were the origin of the different galaxy types that we observe today.
www.fcaglp.unlp.edu.ar /CGGE/Eng/gcdg_obj.html   (589 words)

  
 X-ray Emission from Clusters and Groups of Galaxies
In rich clusters most of the baryonic mass is in the gas phase and the ratio of mass in gas/stars varies by a factor of 2-4.
In a few clusters with published optical velocity dispersion profiles it is possible to perform a comparison of the predicted velocity dispersion profile with the x-ray determined mass profile, under the assumption of isotropic orbits and the agreement is good.
That is, the cluster determined baryonic fraction is not consistent with a closed universe and the big bang nucleosynthesis determined baryonic fraction, nor is the cluster M/L consistent with closure density.
lheawww.gsfc.nasa.gov /users/richard/nas.html   (4551 words)

  
 Groups and Clusters of Galaxies   (Site not responding. Last check: 2007-10-07)
Galaxies do not usually occur as isolated "island universes" in space which which float lonely through an otherwise empty universe, but normally form groups of several individuals, in a wide range from few or few dozens of galaxies to large clusters of up to several thousands.
Our own galaxy, the Milky Way, is also a member of a smaller group of galaxies, the Local Group, which contains three large and over 30 small galaxies.
Together with most nearby galaxy groups (and field galaxies), the Local Group is part of the so-called Local or Virgo Supercluster, which is dominated by the big Virgo Cluster.
www.seds.org /messier/gal_clus.html   (317 words)

  
 Galaxies and the Universe - Galaxy Groups and Clusters
The survey of clusters was extended to the southern sky by Abell, Corwin, and Olowin 1989 (ApJSuppl 70, 1; CDS digital version), producing the first reasonably complete all-sky catalog of nearby clusters (some as far away as z=0.4).
The Local Group is still a dynamically active environment, if we may judge from tidal stripping of M32, the imminent demise of the newly-found Sagittarius dwarf spheroidal from galactic tides, and the material pulled into the Magellanic Stream for the same reason.
I'll stress at the outset that the visible galaxies are such a minor part of the whole assemblages, and are probably even outweighed by the hot intracluster gas, that "cluster of galaxies" is downright misleading, but we're stuck with it.
www.astr.ua.edu /keel/galaxies/clusters.html   (1693 words)

  
 RedShift / News
Clusters of galaxies as diagnostic tools for cosmological research from Astrophysics Research Institute of Liverpool John Moores University.
Lecture on clusters of galaxies by the Institute of Astronomy and Astrophysics of the University of Tübingen.
Scientists of the Astrophysics Group of the Yamagata University report on their activities in the field of nonthermal emission from clusters of galaxies and merger of clusters of galaxies.
www.maris.com /content/news/news.php3?cur=178   (580 words)

  
 Potential PhD Projects (starting October 2004)   (Site not responding. Last check: 2007-10-07)
Early-type galaxies (ellipticals and lenticulars) dominate the population of galaxies in most clusters and groups.
A variety of studies of early-type galaxies are already underway at Birmingham, involving optical imaging and spectroscopy, X-ray observations of the hot gas which often fills them, and stellar population modelling which can be used to reconstruct their star formation history.
The group is active member of the GEO600 collaboration, the LIGO Scientific Collaboration and the LISA International Science Team.
www.sr.bham.ac.uk /phd/projects.html   (1578 words)

  
 Catalogue: VII/28
VII/28 Southern Groups and Clusters of Galaxies (Duus, Newell 1977) ================================================================================ Southern Groups and Clusters of Galaxies Duus A., Newell E.B.
Nevertheless, the clusters and groups are listed from a representative sample of nearby to distant systems that is spread across the southern sky.
Note: not all entries in the catalogue which qualify as previously identified clusters and groups contain data for the fields: ESO number, x and y, T, N and D. References used in these bytes are given in Table 1.
cdsweb.u-strasbg.fr /cgi-bin/Cat?VII/28   (874 words)

  
 Groups of Galaxies containing Messier objects
Galaxies are usually members of groups or clusters, and those listed in Messier's catalog are no exceptions.
HST observations of Cepheids in M100, together with the work of Nial R. Tanvir on the M96 group extrapolated to this cluster, indicate that the Virgo cluster is at a distance of some 60 million light-years.
M104 is the dominating member of a small group called the M104 group or NGC 4594 group of galaxies.
seds.lpl.arizona.edu /messier/g-group.html   (565 words)

  
 Groups and clusters of galaxies: Definition and Links by Encyclopedian.com - All about Groups and clusters of galaxies   (Site not responding. Last check: 2007-10-07)
Groups and clusters of galaxies: Definition and Links by Encyclopedian.com - All about Groups and clusters of galaxies
They have a diameter of about 2 megaparsec (Mpc) (see 1 E22 m for distance comparisons).
Note: clusters of galaxies should not be confused with star clusters such as globular clusters and open clusters, which are structures within galaxies.
www.encyclopedian.com /ga/Galaxy-cluster.html   (453 words)

  
 [No title]
Clusters of galaxies appear to form at the intersections of voids.
Here the spatial distribution of infall galaxies is plotted with heads or tails on them to indicate the amplitude of their infall velocity.
Figure 3-18: Individual galaxy peculiar velocities plotted in comparison with the spherically symmetric infall model that would be generated by a Great Attractor located at kinematic distance of 4350 km/s from the Milky Way.
zebu.uoregon.edu /timages/toc3.html   (1208 words)

  
 ADC Quick Reference: Basic Data on Groups and Clusters of Galaxies   (Site not responding. Last check: 2007-10-07)
J/A+A/312/745 SSRS groups of galaxies redshift neighbourhood (Ramella+, 1996)
J/ApJ/365/66 REDSHIFTS OF DISTANT ABELL CLUSTERS OF GALAXIES (Huchra+ 1990)
J/A+A/278/379 X-ray Emission from Abell Clusters of Galaxies (Briel+ 1993)
adc.gsfc.nasa.gov /adc/quick_ref/ref_clusters.html   (1447 words)

  
 Chandra :: Field Guide to X-ray Sources :: Groups & Clusters of Galaxies   (Site not responding. Last check: 2007-10-07)
X-ray surveys to count the number of large clusters in the universe, astronomers can test the various theories for the content and evolution of the universe.
Chandra observations of the clouds of hot gas in clusters of galaxies will provide other clues to the origin, evolution and destiny of the universe.
microwave observations can measure the effect of the cluster gas as it scatters the cosmic microwave background streaming through the cluster from the depths of the universe.
www.chandra.harvard.edu /xray_sources/galaxy_clusters2.html   (224 words)

  
 Groups and clusters of galaxies - Questionz.net , answers to all your questions   (Site not responding. Last check: 2007-10-07)
Groups of galaxies Groups of galaxies are the smallest aggregates of galaxies.
Clusters of galaxies Clusters are larger than groups, although there is no sharp dividing line between a group and a cluster.
Superclusters Groups, clusters and some isolated galaxies form even larger structures, the superclusters.
www.questionz.net /Universe/Clusters_of_galaxies.html   (628 words)

  
 SCIENTISTS SPEAK ABOUT THE ORIGIN OF MATTER - 2   (Site not responding. Last check: 2007-10-07)
As for the entire galaxy, if there are such things as antimatter stars, some would already have gone supernova, pouring vast quantities of antiparticles into the interstellar medium and thereby producing almost constant matter-antimatter annihilations and their telltale bursts of energy."—*Time-Life, Cosmic Mysteries (1990), pp.
"The large-scale distribution of matter is strikingly clumpy; we see stars in galaxies, galaxies in groups and clusters, and clusters in superclusters."—*P. Peebles, "The Origin of Galaxies and Clusters of Galaxies," in Science, 224 (1984), pp.
The prerequisite for a cosmos with clusters of concentrated matter is inhomogeneity—some irregularity, some departure from uniformity, some wrinkle in the smoothness of space-time—around which matter, forged in the primordial furnace, can accrete.
www.pathlights.com /ce_encyclopedia/01-ma7.htm   (1817 words)

  
 Groups and clusters of galaxies : Galaxy cluster   (Site not responding. Last check: 2007-10-07)
Groups and clusters of galaxies : Galaxy cluster
terms defined : Groups and clusters of galaxies : Galaxy cluster
All is still licensed under the GNU FDL.
www.termsdefined.net /ga/galaxy-cluster.html   (587 words)

  
 Searching Procedures for Groups, Clusters and Superclusters of Galaxies   (Site not responding. Last check: 2007-10-07)
The procedure is consisted of the study of the mutual location of the ranked neighbours of each galaxy (or cluster) and computing the density enhancement over the mean local density, defined for various spheres (from 3 up to 200 Mpc, depending on the hierarchy of the system).
New lists of superclusters of galaxies are also completed on the base of ACO clusters of galaxies.
Some statistics and dynamical characteristics of pairs, groups, clusters, and superclusters of galaxies are presented.
cadcwww.dao.nrc.ca /abstracts/kuneva.tex.html   (295 words)

  
 Scientific activities / Research themes - Galaxies, Groups and clusters   (Site not responding. Last check: 2007-10-07)
The properties of groups and clusters are analyzed under various aspects
Modelling of individual galaxies from optical images, in particular analysis of the properties of ellipticals in clusters
Groups of galaxies as tracers of large scale structure
www.iap.fr /English/ScientificActivities/ResearchThemes/CosmologyStructureUniverse/GroupsClustersGalaxies/galaxies_groups_clusters.html   (122 words)

  
 New Scientist Breaking News - Evidence of dark energy missed 30 years ago
It has been known since the late 1920s that the universe is expanding and that this so-called Hubble expansion is the dominant factor controlling the speed of galaxies in the distant universe.
In 1972, Allan Sandage of the Carnegie Observatories in Pasadena, California, US, reasoned that in the nearby universe - where the expansion is at its slowest - the gravitational attraction between groups and clusters of galaxies should produce significant deviations in their velocities from the otherwise largely smooth speed of expansion.
This is not it." According to Peacock, galaxies naturally form in regions where the gas has cooled and slowed down enough to form stars, and these regions have low peculiar velocities, which can explain the observations.
www.newscientist.com /article.ns?id=dn7109   (560 words)

  
 Population studies in groups and clusters of galaxies. II. A catalog of galaxies in the central 3.5 degs of the Fornax ...
Cluster membership is for the most part based on galaxy morphology.
By virtue of their low surface brightness, dwarf galaxies in the cluster can be distinguished with a high degree of certainty from background galaxies.
Galaxies have been classified in the extended Hubble system, and group memberships have been assigned based on velocity (where available) and morphology.
www.cs.wisc.edu /niagara/data/nasa/7180.xml   (1409 words)

  
 Henry C. Ferguson page on dwarf and LSB galaxies   (Site not responding. Last check: 2007-10-07)
Population studies in groups and clusters of galaxies.
The spatial distributions and intrinsic shapes of dwarf elliptical galaxies in the Virgo and Fornax Clusters Ferguson, H. & Sandage, A., 1989, ApJ, 346, L53.
II - A catalog of galaxies in the central 3.5 deg of the Fornax Cluster Ferguson, H. Population studies in groups and clusters of galaxies.
icarus.stsci.edu /~ferguson/research/dwarflsb.html   (245 words)

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