Defining the limits of galaxy clusters is imprecise as many clusters are still forming. In particular, clusters close to the
Milky Way tend to be classified as galaxy clusters even when they are much smaller than more distant clusters.
Clusters exhibiting strong evidence of dark matter
Some clusters exhibiting strong evidence of
dark matter.
In this collision between two clusters of galaxies, the stars pass between each other unhindered, while the hot, diffuse gas experiences friction and is left behind between the clusters. The gas dominates the visible mass budget of the clusters, being several times more massive than all the stars. Yet the regions with the stars show more gravitational lensing than the gas region, indicating that they are more massive than the gas. Some dark (since we don't see it), collision-less (or it would have been slowed, like the gas) matter is inferred to be present to account for the extra lensing around otherwise low-mass regions.[2]
This is actually a collision between two galaxy clusters. The galaxies and the dark matter seems to have separated out into separate dark and light cores.[3]
This is a recently coalesced merger of galaxy clusters, which has resulted in a ring of dark matter around the galaxies, yet to be redistributed.[4][5]
Named groups and clusters
This is a list of galaxy groups and clusters that are well known by something other than an entry in a catalog or list, or a set of coordinates, or a systematic designation.
Named for its size, El Gordo ("the fat one") is the biggest cluster found in the distant universe (at its distance and beyond), at the time of discovery in 2011, with a mass of 3 quadrillion suns. The second most massive galaxy cluster next to El Gordo is
RCS2 J2327, a
galaxy cluster with the mass of 2 quadrillion suns.
Named in comparison with the Bullet Cluster, being of similar formation, except smaller.
Also has a systematic catalogue name
SL2S J08544-0121. As of 2014, it was the lowest mass object that showed separation between the concentrations of dark matter and baryonic matter in the object.[11][12]
Coined by
Tom Lorenzin (author of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing") to honor Deer Lick Gap in the mountains of North Carolina, from which he had especially fine views of the galaxy group.
Also referred to as the
NGC 7331 Group, after the brightest member of the group.[13]
Named after its discoverer,
Carl Seyfert. At the time it appeared to contain six external nebulae. It is also called the
NGC 6027 Sextet, after its brightest member.
There are actually only five galaxies in the sextet, and only four galaxies in the compact group. One of the galaxies is an ungravitationally bound background object. The other "galaxy" is instead an extension of the interacting system — a
tidal stream caused by the merger. The group is, therefore, more properly called
HCG 79; the name refers to the visual collection and not the group. HCG 79 lies 190 million light-years away in the Serpens Caput constellation.
There are actually only four galaxies in the compact group, the other galaxy is a foreground galaxy. The group is therefore more properly called
HCG 92, because the name refers to a visual collection and not a group. Thus, the real group is also called Stephan's Quartet.
The major nearby groups and clusters are generally named after the constellation they lie in. Many groups are named after the leading galaxy in the group. This represents an ad hoc systematic naming system.
Groups and clusters visible to the unaided eye
The
Local Group contains the largest number of visible galaxies with the naked eye. However, its galaxies are not visually grouped together in the sky, except for the two
Magellanic Clouds. The IC342/
Maffei Group, the nearest galaxy group, would be visible by the naked eye if it were not obscured by the stars and dust clouds in the
Milky Way's
spiral arms.
The
Centaurus A galaxy has been spotted with the naked eye by Stephen James O'Meara [16][17] and
M83 has also reportedly been seen with the naked eye.[18]
Mly represents millions of
light-years, a measure of distance.
Mpc represents millions of
parsecs, a measure of distance (1 Mpc = 3.26 Mly).
z represents
redshift, a measure of recessional velocity and inferred distance due to cosmological expansion. In this very nearby context, however, the observed redshift and recessional velocity are due to the
Doppler shifting of the light.
Distances are measured from Earth, with Earth being at zero.
Attempts at measuring the redshift of the
brightest cluster galaxy of this Hydra Cluster had been attempted for years before it had been successfully achieved. The BCG was also the most distant galaxy of the time.[48][50][51][52]
The BCG for this group was used to measure its redshift. Shortly after this was publicized, it was accepted that redshifts were an acceptable measure of inferred distance.[60]
This was the first noted cluster of "nebulae" that would become galaxies. The first redshifts to galaxies in the cluster were measured in the 1910s. Galaxies were not identified as such until the 1920s. The distance to the Virgo Cluster would have to wait until the 1930s.[21]
Mly represents millions of
light-years, a measure of distance.
Mpc represents millions of
parsecs, a measure of distance.
z represents
redshift, a measure of recessional velocity and inferred distance due to cosmological expansion.
Distances are measured from Earth, with Earth being at zero.
In 1995 and 2001, the cluster around
3C 294 was announced, at z=1.786 [65]
In 1992, observations of the field of cluster
Cl 0939+4713 found what appears to be a background cluster near a quasar, also in the background. The quasar was measured at z=2.055 and it was assumed that the cluster would be as well.[66][67][68][69]
In 1975,
3C 123 and its galaxy cluster was incorrectly determined to lie at z=0.637 (actually z=0.218) [70][71]
In 1958, cluster
Cl 0024+1654 and
Cl 1447+2619 were estimated to have redshifts of z=0.29 and z=0.35 respectively. However, they were not spectroscopically determined.[48]
Farthest protoclusters
5 Farthest protoclusters
Galaxy protocluster
Distance
Notes
No entries yet
Mly represents millions of
light-years, a measure of distance.
Mpc represents millions of
parsecs, a measure of distance.
z represents
redshift, a measure of recessional velocity and inferred distance due to cosmological expansion.
Distances are measured from Earth, with Earth being at zero.
z represents
redshift, a measure of recessional velocity and inferred distance due to cosmological expansion.
Distances are measured from Earth, with Earth being at zero.
In 2002, a very large, very rich protocluster, or the most distant protosupercluster was found in the field of galaxy cluster
MS 1512+36, around the gravitationally lensed galaxy
MS 1512-cB58, at z=2.724 [78][80]
False clusters
Sometimes clusters are put forward that are not genuine clusters or superclusters. Through the researching of member positions,
distances,
peculiar velocities, and
binding mass, former clusters are sometimes found to be the product of a chance line-of-sight superposition.
^
abcBiviano, Andrea; et al. (2000). "From Messier to Abell: 200 years of science with galaxy clusters". In Florence Durret; Daniel Gerbal (eds.). Constructing the Universe with Clusters of Galaxies, IAP 2000 meeting, Paris, France, July 2000. p. 1.
arXiv:astro-ph/0010409.
Bibcode:
2000cucg.confE...1B. {{
cite book}}: |journal= ignored (
help)
^
abMAX-PLANCK-INSTITUT FÜR EXTRATERRESTRISCHE PHYSIK, GARCHING, GERMANY; DEPARTMENT OF ASTRONOMY, UNIVERSITY OF MICHIGAN, ANN ARBOR, USA; ESO, ASTROPHYSIKALISCHES INSTITUT, POTSDAM, GERMANY;
"GALAXY CLUSTER ARCHAEOLOGY"(PDF). Archived from
the original(PDF) on 2006-06-22. ; HANS BÖHRINGER, CHRISTOPHER MULIS, PIERO ROSATI, GEORG LAMER, RENE FASSBENDER, AXEL SCHWOPE, PETER SCHUECKER
^
abcSandage, Allan (1961). "The Ability of the 200-INCH Telescope to Discriminate Between Selected World Models". The Astrophysical Journal. 133: 355.
Bibcode:
1961ApJ...133..355S.
doi:
10.1086/147041.
^
abChant, C. A. (1932). "Notes and Queries (Doings at Mount Wilson-Ritchey's Photographic Telescope-Infra-red Photographic Plates)". Journal of the Royal Astronomical Society of Canada. 26: 180.
Bibcode:
1932JRASC..26..180C.
^Hubble, Edwin; Humason, Milton L. (1931). "The Velocity-Distance Relation among Extra-Galactic Nebulae". The Astrophysical Journal. 74: 43.
Bibcode:
1931ApJ....74...43H.
doi:
10.1086/143323.
^
abHumason, M. L. (1931). "The Large Apparent Velocities of Extra-Galactic Nebulae". Leaflet of the Astronomical Society of the Pacific. 1 (37): 149.
Bibcode:
1931ASPL....1..149H.
^Dressler, A. (1993). "The Spectra and Morphology of Galaxies in High-Redshift Clusters". Observational Cosmology. 51: 225.
Bibcode:
1993ASPC...51..225D.
Defining the limits of galaxy clusters is imprecise as many clusters are still forming. In particular, clusters close to the
Milky Way tend to be classified as galaxy clusters even when they are much smaller than more distant clusters.
Clusters exhibiting strong evidence of dark matter
Some clusters exhibiting strong evidence of
dark matter.
In this collision between two clusters of galaxies, the stars pass between each other unhindered, while the hot, diffuse gas experiences friction and is left behind between the clusters. The gas dominates the visible mass budget of the clusters, being several times more massive than all the stars. Yet the regions with the stars show more gravitational lensing than the gas region, indicating that they are more massive than the gas. Some dark (since we don't see it), collision-less (or it would have been slowed, like the gas) matter is inferred to be present to account for the extra lensing around otherwise low-mass regions.[2]
This is actually a collision between two galaxy clusters. The galaxies and the dark matter seems to have separated out into separate dark and light cores.[3]
This is a recently coalesced merger of galaxy clusters, which has resulted in a ring of dark matter around the galaxies, yet to be redistributed.[4][5]
Named groups and clusters
This is a list of galaxy groups and clusters that are well known by something other than an entry in a catalog or list, or a set of coordinates, or a systematic designation.
Named for its size, El Gordo ("the fat one") is the biggest cluster found in the distant universe (at its distance and beyond), at the time of discovery in 2011, with a mass of 3 quadrillion suns. The second most massive galaxy cluster next to El Gordo is
RCS2 J2327, a
galaxy cluster with the mass of 2 quadrillion suns.
Named in comparison with the Bullet Cluster, being of similar formation, except smaller.
Also has a systematic catalogue name
SL2S J08544-0121. As of 2014, it was the lowest mass object that showed separation between the concentrations of dark matter and baryonic matter in the object.[11][12]
Coined by
Tom Lorenzin (author of "1000+ The Amateur Astronomers' Field Guide to Deep Sky Observing") to honor Deer Lick Gap in the mountains of North Carolina, from which he had especially fine views of the galaxy group.
Also referred to as the
NGC 7331 Group, after the brightest member of the group.[13]
Named after its discoverer,
Carl Seyfert. At the time it appeared to contain six external nebulae. It is also called the
NGC 6027 Sextet, after its brightest member.
There are actually only five galaxies in the sextet, and only four galaxies in the compact group. One of the galaxies is an ungravitationally bound background object. The other "galaxy" is instead an extension of the interacting system — a
tidal stream caused by the merger. The group is, therefore, more properly called
HCG 79; the name refers to the visual collection and not the group. HCG 79 lies 190 million light-years away in the Serpens Caput constellation.
There are actually only four galaxies in the compact group, the other galaxy is a foreground galaxy. The group is therefore more properly called
HCG 92, because the name refers to a visual collection and not a group. Thus, the real group is also called Stephan's Quartet.
The major nearby groups and clusters are generally named after the constellation they lie in. Many groups are named after the leading galaxy in the group. This represents an ad hoc systematic naming system.
Groups and clusters visible to the unaided eye
The
Local Group contains the largest number of visible galaxies with the naked eye. However, its galaxies are not visually grouped together in the sky, except for the two
Magellanic Clouds. The IC342/
Maffei Group, the nearest galaxy group, would be visible by the naked eye if it were not obscured by the stars and dust clouds in the
Milky Way's
spiral arms.
The
Centaurus A galaxy has been spotted with the naked eye by Stephen James O'Meara [16][17] and
M83 has also reportedly been seen with the naked eye.[18]
Mly represents millions of
light-years, a measure of distance.
Mpc represents millions of
parsecs, a measure of distance (1 Mpc = 3.26 Mly).
z represents
redshift, a measure of recessional velocity and inferred distance due to cosmological expansion. In this very nearby context, however, the observed redshift and recessional velocity are due to the
Doppler shifting of the light.
Distances are measured from Earth, with Earth being at zero.
Attempts at measuring the redshift of the
brightest cluster galaxy of this Hydra Cluster had been attempted for years before it had been successfully achieved. The BCG was also the most distant galaxy of the time.[48][50][51][52]
The BCG for this group was used to measure its redshift. Shortly after this was publicized, it was accepted that redshifts were an acceptable measure of inferred distance.[60]
This was the first noted cluster of "nebulae" that would become galaxies. The first redshifts to galaxies in the cluster were measured in the 1910s. Galaxies were not identified as such until the 1920s. The distance to the Virgo Cluster would have to wait until the 1930s.[21]
Mly represents millions of
light-years, a measure of distance.
Mpc represents millions of
parsecs, a measure of distance.
z represents
redshift, a measure of recessional velocity and inferred distance due to cosmological expansion.
Distances are measured from Earth, with Earth being at zero.
In 1995 and 2001, the cluster around
3C 294 was announced, at z=1.786 [65]
In 1992, observations of the field of cluster
Cl 0939+4713 found what appears to be a background cluster near a quasar, also in the background. The quasar was measured at z=2.055 and it was assumed that the cluster would be as well.[66][67][68][69]
In 1975,
3C 123 and its galaxy cluster was incorrectly determined to lie at z=0.637 (actually z=0.218) [70][71]
In 1958, cluster
Cl 0024+1654 and
Cl 1447+2619 were estimated to have redshifts of z=0.29 and z=0.35 respectively. However, they were not spectroscopically determined.[48]
Farthest protoclusters
5 Farthest protoclusters
Galaxy protocluster
Distance
Notes
No entries yet
Mly represents millions of
light-years, a measure of distance.
Mpc represents millions of
parsecs, a measure of distance.
z represents
redshift, a measure of recessional velocity and inferred distance due to cosmological expansion.
Distances are measured from Earth, with Earth being at zero.
z represents
redshift, a measure of recessional velocity and inferred distance due to cosmological expansion.
Distances are measured from Earth, with Earth being at zero.
In 2002, a very large, very rich protocluster, or the most distant protosupercluster was found in the field of galaxy cluster
MS 1512+36, around the gravitationally lensed galaxy
MS 1512-cB58, at z=2.724 [78][80]
False clusters
Sometimes clusters are put forward that are not genuine clusters or superclusters. Through the researching of member positions,
distances,
peculiar velocities, and
binding mass, former clusters are sometimes found to be the product of a chance line-of-sight superposition.
^
abcBiviano, Andrea; et al. (2000). "From Messier to Abell: 200 years of science with galaxy clusters". In Florence Durret; Daniel Gerbal (eds.). Constructing the Universe with Clusters of Galaxies, IAP 2000 meeting, Paris, France, July 2000. p. 1.
arXiv:astro-ph/0010409.
Bibcode:
2000cucg.confE...1B. {{
cite book}}: |journal= ignored (
help)
^
abMAX-PLANCK-INSTITUT FÜR EXTRATERRESTRISCHE PHYSIK, GARCHING, GERMANY; DEPARTMENT OF ASTRONOMY, UNIVERSITY OF MICHIGAN, ANN ARBOR, USA; ESO, ASTROPHYSIKALISCHES INSTITUT, POTSDAM, GERMANY;
"GALAXY CLUSTER ARCHAEOLOGY"(PDF). Archived from
the original(PDF) on 2006-06-22. ; HANS BÖHRINGER, CHRISTOPHER MULIS, PIERO ROSATI, GEORG LAMER, RENE FASSBENDER, AXEL SCHWOPE, PETER SCHUECKER
^
abcSandage, Allan (1961). "The Ability of the 200-INCH Telescope to Discriminate Between Selected World Models". The Astrophysical Journal. 133: 355.
Bibcode:
1961ApJ...133..355S.
doi:
10.1086/147041.
^
abChant, C. A. (1932). "Notes and Queries (Doings at Mount Wilson-Ritchey's Photographic Telescope-Infra-red Photographic Plates)". Journal of the Royal Astronomical Society of Canada. 26: 180.
Bibcode:
1932JRASC..26..180C.
^Hubble, Edwin; Humason, Milton L. (1931). "The Velocity-Distance Relation among Extra-Galactic Nebulae". The Astrophysical Journal. 74: 43.
Bibcode:
1931ApJ....74...43H.
doi:
10.1086/143323.
^
abHumason, M. L. (1931). "The Large Apparent Velocities of Extra-Galactic Nebulae". Leaflet of the Astronomical Society of the Pacific. 1 (37): 149.
Bibcode:
1931ASPL....1..149H.
^Dressler, A. (1993). "The Spectra and Morphology of Galaxies in High-Redshift Clusters". Observational Cosmology. 51: 225.
Bibcode:
1993ASPC...51..225D.