Abell 2218

{{Short description|Galaxy cluster in the constellation Draco}} {{Galaxy cluster | name = Abell 2218 | image = Abell NGC2218 hst big.jpg | caption = Abell 2218. Credit: [[NASA]]/[[ESA]] | epoch =[[Epoch (astronomy)#Julian years and J2000|J2000]] | ra = {{RA|16|35|54}}<ref name="NED">{{cite web | title = NASA/IPAC Extragalactic Database | work = Results for Abell 2218 | url = http://nedwww.ipac.caltech.edu/ | access-date = 2006-09-18}}</ref> | dec = {{DEC|+66|13|00}}<ref name="NED" /> | constellation = [[Draco (constellation)|Draco]] | brightest_member = | member_no = ~10,000 | richness = 4<ref name="ACO">{{cite journal | last1 = Abell | first1 = George O. | author-link1 = George O. Abell | last2 = Corwin | first2 = Harold G. Jr. | author-link2 = Harold G. Corwin | last3 = Olowin | first3 = Ronald P. | author-link3 = Ronald P. Olowin |date=May 1989 | title = A catalog of rich clusters of galaxies | journal = Astrophysical Journal Supplement Series | volume = 70 | issue = May 1989 | pages = 1–138 | issn = 0067-0049 | bibcode = 1989ApJS...70....1A | doi = 10.1086/191333 | doi-access = free }}</ref> | bmtype = II <ref name="ACO" /> | redshift = 0.17560<ref name="NED" /> | distance = {{convert|719|Mpc|Mly|0|abbr=on|lk=on}} {{hub|0.705}}<ref name="NED" /> | flux = (7.50 ± 9.1%){{e|-12}} [[erg]] s<sup>−1</sup> cm<sup>−2</sup> (0.1–2.4 [[electron volt|keV]]) <ref name="NED" /> | other_names = }}

'''Abell 2218''' is a large [[Galaxy cluster|cluster of galaxies]] over [[10 zettametres|2 billion]] [[light-year]]s away in the [[constellation]] [[Draco (constellation)|Draco]].

Acting as a powerful [[Gravitational lens|lens]], it magnifies and distorts all galaxies lying behind the cluster core into long [[Arc (geometry)|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]].<ref>[https://web.archive.org/web/20140221090216/http://www.nbcnews.com/id/4274187/ NBC News: "Galaxy ranks as most distant object in cosmos"]</ref>

The [[color]] of the lensed galaxies is a function of their distances and types. The [[Orange (colour)|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.<ref>{{Cite journal|last1=Kneib|first1=Jean-Paul|last2=Ellis|first2=Richard S.|last3=Santos|first3=Michael R.|last4=Richard|first4=Johan|date=2004|title=A Probable z~7 Galaxy Strongly Lensed by the Rich Cluster A2218: Exploring the Dark Ages|journal=The Astrophysical Journal|volume=607|issue=2|pages=697–703|doi=10.1086/386281|arxiv=astro-ph/0402319|bibcode=2004ApJ...607..697K|s2cid=14981473}}</ref>

==Dark matter== Clusters of galaxies such as Abell 2218 have also been used to infer both the amount<ref>{{Cite journal|last1=Kneib|first1=Jean-Paul|date=1995|title=Dynamics of Abell 2218 from optical and near-IR imagery of arc(let)s and the Rosat/HRI X-ray map|journal=Astronomy and Astrophysics|volume=303|pages=27–40|bibcode=1995A&A...303...27K|arxiv=astro-ph/9504038}}</ref><ref>{{Cite journal|last1=Squires|first1=G.|last2=Kaiser|first2=N.|last3=Babul|first3=A.|last4=Fahlman|first4=G.|last5=Woods|first5=D.|last6=Neumann|first6=D.|last7=Böhringer|first7=H.|date=1996|title=The dark matter, gas, and galaxy distributions in Abell 2218: A weak gravitational lensing and X-ray analysis|journal=The Astrophysical Journal|volume=461|pages=572–586|doi=10.1086/177085|arxiv=astro-ph/9507008|bibcode=1996ApJ...461..572S|s2cid=18973537}}</ref> and distribution<ref>{{Cite journal|last1=Abdelsalam|first1=Hanadi M.|last2=Saha|first2=Prasenjit|last3=Williams|first3=Liliya L. R.|date=1998|title=Non-parametric reconstruction of Abell 2218 from combined weak and strong lensing|journal=The Astronomical Journal|volume=116|issue=4|pages=1541–1552|doi=10.1086/300546|arxiv=astro-ph/9806244|bibcode=1998AJ....116.1541A|s2cid=15908226}}</ref><ref>{{Cite journal|last1=Shan|first1=Huanyuan|last2=Qin|first2=Bo|last3=Fort|first3=Bernard|last4=Tao|first4=Charling|last5=Wu|first5=Xiang-Ping|last6=Zhao|first6=Hongsheng|date=2010|title=Offset between dark matter and ordinary matter: evidence from a sample of 38 lensing clusters of galaxies|journal=Monthly Notices of the Royal Astronomical Society|volume=406|issue=2|pages=1134–1139|doi=10.1111/j.1365-2966.2010.16739.x|doi-access=free |arxiv=1004.1475|bibcode=2010MNRAS.406.1134S|s2cid=119255830}}</ref><ref>{{Cite journal|last1=Lorenz|first1=Suzanne|last2=Peterson|first2=J. R.|date=2013|title=New Techniques in Dark Matter Mapping|journal=American Astronomical Society|volume=222|issue=id.103.02|pages=103.02|bibcode=2013AAS...22210302L}}</ref> of [[Dark matter]].

==See also== * [[Abell 370]] * [[Abell 1689]] * [[Abell 1835 IR1916]] * [[Abell catalogue]] * [[GRB 090423]] * [[IOK-1]] * [[UDFy-38135539]] * [[X-ray astronomy]]

==References== {{Reflist}}

==External links== {{commonscat}} *[http://www.spacetelescope.org/news/html/heic0113.html Release about Abell 2218 at ESA/Hubble] *[[Astronomy Picture of the Day]] - [http://apod.nasa.gov/apod/ap100620.html Abell 2218: A Galaxy Cluster Lens] - 2010 June 20

{{DEFAULTSORT:Abell 2218}} [[Category:Draco (constellation)]] [[Category:Abell objects|2218]] [[Category:Abell richness class 4]] [[Category:Galaxy clusters]]