# Galaxy filament

In physical cosmology, galaxy filaments (subtypes: supercluster complexes, galaxy walls, and galaxy sheets)[1][2] are the largest known structures in the universe. They are massive, thread-like formations, with a typical length of 50 to 80 megaparsecs h−1 (163 to 261 million light-years) that form the boundaries between large voids in the universe.[3] Filaments consist of gravitationally bound galaxies. Parts wherein many galaxies are very close to one another (in cosmic terms) are called superclusters.

## Formation

In the standard model of the evolution of the universe, galactic filaments form along and follow web-like strings of dark matter.[4] It is thought that this dark matter dictates the structure of the Universe on the grandest of scales. Dark matter gravitationally attracts baryonic matter, and it is this "normal" matter that astronomers see forming long, thin walls of super-galactic clusters.

## Discovery

Discovery of structures larger than superclusters began in the late-1980s. In 1987, astronomer R. Brent Tully of the University of Hawaii's Institute of Astronomy identified what he called the Pisces–Cetus Supercluster Complex. In 1989, the CfA2 Great Wall was discovered,[5] followed by the Sloan Great Wall in 2003.[6] On January 11, 2013, researchers led by Roger Clowes of the University of Central Lancashire announced the discovery of a large quasar group, the Huge-LQG, which dwarfs previously discovered galaxy filaments in size.[7] In November 2013, using gamma-ray bursts as reference points, astronomers discovered the Hercules–Corona Borealis Great Wall, an extremely huge filament measuring more than 10 billion light-years across.[8][9][10]

## Filaments

Filament subtype of filaments have roughly similar major and minor axes in cross-section, along the lengthwise axis.

Filaments of Galaxies
Filament Date Mean distance Dimension Notes
Coma Filament The Coma Supercluster lies within the Coma Filament.[11] It forms part of the CfA2 Great Wall.[12]
Perseus–Pegasus Filament 1985 Connected to the Pisces–Cetus Supercluster, with the Perseus–Pisces Supercluster being a member of the filament.[13]
Ursa Major Filament Connected to the CfA Homunculus, a portion of the filament forms a portion of the "leg" of the Homunculus.[14]
Lynx–Ursa Major Filament (LUM Filament) 1999 from 2000 km/s to 8000 km/s in redshift space Connected to and separate from the Lynx–Ursa Major Supercluster.[14]
z=2.38 filament around protocluster ClG J2143-4423 2004 z=2.38 110Mpc A filament the length of the Great Wall was discovered in 2004. As of 2008, it was still the largest structure beyond redshift 2.[15][16][17][18]
• A short filament, detected by identifying an alignment of star-forming galaxies, in the neighborhood of the Milky Way and the Local Group was proposed by Adi Zitrin and Noah Brosch.[19] The reality of this filament, and the identification of a similar but shorter filament, were the result of a study by McQuinn et al. (2014) based on distance measurements using the TRGB method.[20]

### Galaxy walls

The galaxy wall subtype of filaments have a significantly greater major axis than minor axis in cross-section, along the lengthwise axis.

Walls of Galaxies
Wall Date Mean distance Dimension Notes
CfA2 Great Wall (Coma Wall, Great Wall, Northern Great Wall, Great Northern Wall, CfA Great Wall) 1989 z=0.03058 251Mpc long
750 Mly long
250 Mly wide
20 Mly thick
This was the first super-large large-scale structure or pseudo-structure in the universe to be discovered. The CfA Homunculus lies at the heart of the Great Wall, and the Coma Supercluster forms most of the homunculus structure. The Coma Cluster lies at the core.[21][22]
Sloan Great Wall (SDSS Great Wall) 2003 z=0.07804 433Mpc long This was the largest known galaxy filament to be discovered,[21] until it was eclipsed by the Hercules–Corona Borealis Great Wall found ten years later.
Sculptor Wall (Southern Great Wall, Great Southern Wall, Southern Wall) 8000 km/s long
5000 km/s wide
1000 km/s deep
(in redshift space dimensions)
The Sculptor Wall is "parallel" to the Fornax Wall and "perpendicular" to the Grus Wall.[23][24]
Grus Wall The Grus Wall is "perpendicular" to the Fornax and Sculptor Walls.[24]
Fornax Wall The Fornax Cluster is part of this wall. The wall is "parallel" to the Sculptor Wall and "perpendicular" to the Grus Wall.[23][24]
Hercules–Corona Borealis Great Wall 2013 z≈2[9] 3 Gpc long,[9]
150 000 km/s deep[9]
(in redshift space)
The largest known structure in the universe.[8][9][10] This is also the first time since 1991 that a galaxy filament/great wall held the record as the largest known structure in the universe.
Galaxy filaments, walls and voids form web-like structures.
• A "Centaurus Great Wall" (or "Fornax Great Wall" or "Virgo Great Wall") has been proposed, which would include the Fornax Wall as a portion of it (visually created by the Zone of Avoidance) along with the Centaurus Supercluster and the Virgo Supercluster also known as our Local Supercluster within which the Milky Way galaxy is located (implying this to be the Local Great Wall).[23][24]
• A wall was proposed to be the physical embodiment of the Great Attractor, with the Norma Cluster as part of it. It is sometimes referred to as the Great Attractor Wall or Norma Wall.[25] This suggestion was superseded by the proposal of a supercluster, Laniakea, that would encompass the Great Attractor, Virgo Supercluster, Hydra-Centaurus Superclusters.[26]
• A wall was proposed in 2000 to lie at z=1.47 in the vicinity of radio galaxy B3 0003+387.[27]
• A wall was proposed in 2000 to lie at z=0.559 in the northern Hubble Deep Field (HDF North).[28][29]

#### Map of nearest galaxy walls

The Universe within 500 million light years, showing the nearest galaxy walls

### Large Quasar Groups

Large quasar groups (LQGs) are some of the largest structures known.[30] They are theorized to be protohyperclusters/proto-supercluster-complexes/galaxy filament precursors.[31]

Large Quasar Groups
LQG Date Mean distance Dimension Notes
Clowes–Campusano LQG
(U1.28, CCLQG)
1991 z=1.28
• longest dimension: 630 Mpc
It was the largest known structure in the universe from 1991 to 2011, until U1.11's discovery.
U1.11 2011 z=1.11
• longest dimension: 780 Mpc
Was the largest known structure in the universe for a few months, until Huge-LQG's discovery.
Huge-LQG 2012 z=1.27
• characteristic size: 500 Mpc
• longest dimension: 1240 Mpc
It was the largest structure known in the universe,[30][31] until the discovery of the Hercules–Corona Borealis Great Wall found one year later.[9]

### Supercluster complex

Supercluster complex
Name Date Mean distance Dimension Notes
Pisces–Cetus Supercluster Complex 1987 1 billion ly wide,
150 million ly deep
Contains Virgo Supercluster and Local Group

## Maps of large-scale distribution

The universe within 1 billion light-years (307 Mpc) of Earth, showing local superclusters forming filaments and voids

Map of nearest walls, voids and superclusters

2dF survey map, containing the SDSS Great Wall

2MASS XSC infrared sky map

## References

1. ^ Boris V. Komberg, Andrey V. Kravtsov, Vladimir N. Lukash; "The search and investigation of the Large Groups of Quasars" arXiv:astro-ph/9602090; Bibcode1996astro.ph..2090K;
2. ^ R.G. Clowes; "Large Quasar Groups - A Short Review"; The New Era of Wide Field Astronomy, ASP Conference Series, Vol. 232.; 2001; Astronomical Society of the Pacific; ISBN 1-58381-065-X ; Bibcode2001ASPC..232..108C
3. ^ Bharadwaj, Somnath; Bhavsar, Suketu; Sheth, Jatush V (2004). "The Size of the Longest Filaments in the Universe" (PDF). Astrophys J. 606 (1): 25–31. arXiv:astro-ph/0311342. Bibcode:2004ApJ...606...25B. doi:10.1086/382140.
4. ^ Riordan, Michael; David N. Schramm (March 1991). Shadows of Creation: Dark Matter and the Structure of the Universe. W H Freeman & Co (Sd). ISBN 0-7167-2157-0.
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6. ^ Sky and Telescope, "Refining the Cosmic Recipe", 14 November 2003
7. ^ Wall, Mike (2013-01-11). "Largest structure in universe discovered". Fox News.
8. ^ a b Horvath, Istvan; Hakkila, Jon; Bagoly, Zsolt (2014). "Possible structure in the GRB sky distribution at redshift two". Astronomy & Astrophysics. 561: id.L12. arXiv:1401.0533. Bibcode:2014A&A...561L..12H. doi:10.1051/0004-6361/201323020.
9. Horvath I., Hakkila J., and Bagoly Z.; Hakkila, J.; Bagoly, Z. (2013). "The largest structure of the Universe, defined by Gamma-Ray Bursts". 7th Huntsville Gamma-Ray Burst Symposium, GRB 2013: paper 33 in eConf Proceedings C1304143. 1311: 1104. arXiv:1311.1104. Bibcode:2013arXiv1311.1104H.CS1 maint: Multiple names: authors list (link)
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12. ^ THE ASTRONOMICAL JOURNAL, 115:1745-1777, 1998 May ; THE STAR FORMATION PROPERTIES OF DISK GALAXIES: Hα IMAGING OF GALAXIES IN THE COMA SUPERCLUSTER
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17. ^ "The Distribution of Lyα‐emitting Galaxies at z =2.38. II. Spectroscopy". The Astrophysical Journal. 614: 75–83. arXiv:astro-ph/0406413. Bibcode:2004ApJ...614...75F. doi:10.1086/423417.
18. ^ Relativistic Astrophysics Legacy and Cosmology - Einstein's, ESO Astrophysics Symposia, Volume . ISBN 978-3-540-74712-3. Springer-Verlag Berlin Heidelberg, 2008, p. 358 "Ultraviolet-Bright, High-Redshift ULIRGS" 00/2008 Bibcode2008ralc.conf..358W
19. ^ Zitrin, A.; Brosch, N. (2008). "The NGC 672 and 784 galaxy groups: evidence for galaxy formation and growth along a nearby dark matter filament". Monthly Notices of the Royal Astronomical Society. 390: 408–420. arXiv:0808.1789. Bibcode:2008MNRAS.390..408Z. doi:10.1111/j.1365-2966.2008.13786.x.
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