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Abell 2218
Abell 2218
	Abell 2218. Credit: NASA/ESA
Observation data (Epoch J2000)
Constellation(s)	Draco
Right ascension	16h 35m 54s
Declination	+66° 13′ 00″
Number of galaxies	~10,000
Richness class	4
Bautz–Morgan classification	II
Redshift	0.17560
Distance	719 Mpc (2,345 Mly) h−1; 0.705
X-ray flux	(7.50 ± 9.1%)×10−12 erg s−1 cm−2 (0.1–2.4 keV)

Abell 2218 is a large cluster of galaxies over 2 billion light-years away in the constellation Draco.

Acting as a powerful lens, it magnifies and distorts all galaxies lying behind the cluster core into long arcs. The lensed galaxies are all stretched along the cluster's center and some of them are multiply imaged. Those multiple images usually appear as a pair of images with a third — generally fainter — counter image, as is the case for the very distant object. The lensed galaxies are particularly numerous, as we are looking in between two mass clumps, in a saddle region where the magnification is quite large.

Gravitational lensing

Abell 2218 was used as a gravitational lens to discover the most distant known object in the universe as of 2004. The object, a galaxy some 13 billion years old, is seen from Earth as it would have been just 750 million years after the Big Bang.^[3]

The color of the lensed galaxies is a function of their distances and types. The orange arc is an elliptical galaxy at moderate redshift (z=0.7). The blue arcs are star-forming galaxies at intermediate redshift (z=1–2.5). There is a pair of images in the lower part of the picture of the newly discovered star-forming galaxy at about redshift 7.^[4]

Dark matter

Clusters of galaxies such as Abell 2218 have also been used to infer both the amount^[5]^[6] and distribution^[7]^[8]^[9] of Dark matter.

References

^ ^a ^b ^c ^d ^e "NASA/IPAC Extragalactic Database". Results for Abell 2218. Retrieved 2006-09-18.
^ ^a ^b Abell, George O.; Corwin, Harold G. Jr.; Olowin, Ronald P. (May 1989). "A catalog of rich clusters of galaxies". Astrophysical Journal Supplement Series. 70 (May 1989): 1–138. Bibcode:1989ApJS...70....1A. doi:10.1086/191333. ISSN 0067-0049.
^ NBC News: "Galaxy ranks as most distant object in cosmos"
^ Kneib, Jean-Paul; Ellis, Richard S.; Santos, Michael R.; Richard, Johan (2004). "A Probable z~7 Galaxy Strongly Lensed by the Rich Cluster A2218: Exploring the Dark Ages". The Astrophysical Journal. 607 (2): 697–703. arXiv:astro-ph/0402319. Bibcode:2004ApJ...607..697K. doi:10.1086/386281. S2CID 14981473.
^ Kneib, Jean-Paul (1995). "Dynamics of Abell 2218 from optical and near-IR imagery of arc(let)s and the Rosat/HRI X-ray map". Astronomy and Astrophysics. 303: 27–40. arXiv:astro-ph/9504038. Bibcode:1995A&A...303...27K.
^ Squires, G.; Kaiser, N.; Babul, A.; Fahlman, G.; Woods, D.; Neumann, D.; Böhringer, H. (1996). "The dark matter, gas, and galaxy distributions in Abell 2218: A weak gravitational lensing and X-ray analysis". The Astrophysical Journal. 461: 572–586. arXiv:astro-ph/9507008. Bibcode:1996ApJ...461..572S. doi:10.1086/177085. S2CID 18973537.
^ Abdelsalam, Hanadi M.; Saha, Prasenjit; Williams, Liliya L. R. (1998). "Non-parametric reconstruction of Abell 2218 from combined weak and strong lensing". The Astronomical Journal. 116 (4): 1541–1552. arXiv:astro-ph/9806244. Bibcode:1998AJ....116.1541A. doi:10.1086/300546. S2CID 15908226.
^ Shan, Huanyuan; Qin, Bo; Fort, Bernard; Tao, Charling; Wu, Xiang-Ping; Zhao, Hongsheng (2010). "Offset between dark matter and ordinary matter: evidence from a sample of 38 lensing clusters of galaxies". Monthly Notices of the Royal Astronomical Society. 406 (2): 1134–1139. arXiv:1004.1475. Bibcode:2010MNRAS.406.1134S. doi:10.1111/j.1365-2966.2010.16739.x. S2CID 119255830.
^ Lorenz, Suzanne; Peterson, J. R. (2013). "New Techniques in Dark Matter Mapping". American Astronomical Society. 222 (id.103.02): 103.02. Bibcode:2013AAS...22210302L.