Arp 104

{{Short description|Pair of galaxies in the constellation of Ursa Major}}

{{Infobox Galaxy

|name=Arp 104

|image=NGC 5216 from the Schulman 0.8m Telescope at the Mount Lemmon Skycenter courtesy Adam Block.jpg

|caption=NGC 5216: The Keenan System, Arp 104

|credit=

|epoch=J2000

|constellation name=Ursa Major

|ra={{RA|13|32|08.9}}{{cite web

|url=http://nedwww.ipac.caltech.edu/cgi-bin/nph-objsearch?objname=arp+104&extend=yes&out_csys=Equatorial&out_equinox=J2000.0&obj_sort=RA+or+Longitude&of=pre_text&zv_breaker=30000.0&list_limit=5&img_stamp=YES

|title=Searching NED for object "ARP 104*"

|accessdate=2008-08-02

|work=NASA/IPAC Extragalactic Database (NED)

|publisher=Jet Propulsion Laboratory, California Institute of Technology}}

|dec={{DEC|+62|44|02}}

|z=0.010817

|dist_ly=1.73 × 10⁷

|type=E0/SBb-pec{{cite arXiv

|eprint=astro-ph/0605015

|title=Imaging and spectroscopy of Arp 104: a post-starburst interacting pair with cross-fuelling?

|last=Roche

|first=Nathan

|date=2006-04-29

}}

|appmag_v=14.0{{cite web

|url=http://seds.org/~spider/ngc/ngc.cgi?5216

|archive-url=https://archive.today/20121228035147/http://seds.org/~spider/ngc/ngc.cgi?5216

|url-status=dead

|archive-date=2012-12-28

|title=NGC 5216

|accessdate=2008-08-03

|work=The interactive NGC catalog online

|publisher=Students for the Exploration and Development of Space (SEDS)

}}/12.3{{cite web

|url=http://seds.org/~spider/ngc/ngc.cgi?5218

|archive-url=https://archive.today/20121221001410/http://seds.org/~spider/ngc/ngc.cgi?5218

|url-status=dead

|archive-date=2012-12-21

|title=NGC 5218

|accessdate=2008-08-03

|work=The interactive NGC catalog online

|publisher=Students for the Exploration and Development of Space (SEDS)

}}

|size_v=

|notes=bridged

|names=Keenan's system

NGC 5216/NGC 5218

UGC 8528/UGC 8529{{cite arXiv

|eprint=astro-ph/9911186

|title=The molecular gas-star formation connection in an optically-selected sample of interacting galaxies

|last=Bushouse

|first=Howard A. |author2=Steven D. Lord |author3=Susan A. Lamb |author4=Michael W. Werner |author5=K. Y. Lo

|date=1999-11-10

}}

VV 33a{{cite web

|url=http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=NGC+5216#lab_ident

|title=VV 33a -- Interacting Galaxies

|accessdate=2009-01-14

|work=SIMBAD astronomical object database

|publisher=Centre de Données astronomiques de Strasbourg}}/VV 33b{{cite web

|url=http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=NGC+5218#lab_ident

|title=NGC 5218 -- Galaxy in Pair of Galaxies

|accessdate=2009-01-14

|work=SIMBAD astronomical object database

|publisher=Centre de Données astronomiques de Strasbourg}}}}

Arp 104, also known as Keenan's system, is entry 104 in Halton Arp's Atlas of Peculiar Galaxies catalog for spiral galaxy NGC 5216 and globular galaxy NGC 5218.{{cite web

|url=http://www.universetoday.com/2008/07/25/bridge-across-space-keenans-system-by-martin-winder-and-dietmar-hager/

|title=Bridge Across Space: "Keenan's System" by Martin Winder and Dietmar Hager

|accessdate=2008-08-02

|last=Plotner

|first=Tammy

|date=2008-07-25

|publisher=Universe Today

|archiveurl=https://web.archive.org/web/20080730141220/http://www.universetoday.com/2008/07/25/bridge-across-space-keenans-system-by-martin-winder-and-dietmar-hager/

|archivedate=2008-07-30

|url-status=live

}} The two galaxies are joined by a bridge of galactic material spanning 22 000 light years.{{cite book

|last=Zwicky

|first=Fritz

|title=Ergebnisse der Exakten Naturwissenschaften

|authorlink=Fritz Zwicky

|year=1956

|chapter=Multiple galaxies

|volume=29

|pages=361

|bibcode=1956ErNW...29..344Z

|doi=10.1007/BFb0118841

|isbn=978-3-540-74717-8}}

In 1790 William Herschel discovered the galaxies, and in 1926 they were studied by Edwin Hubble. In 1935 Philip C. Keenan first published a paper about the bridge connecting the galaxies,{{cite journal

|last=Keenan

|first=Philip C.

|date=May 1935

|title=An unusual pair of nebulae: NGC 5216 and 5218

|journal=Astrophysical Journal

|volume=81

|pages=355

|doi=10.1086/143641

|bibcode=1935ApJ....81..355K

}} which was rediscovered in 1958 at the Lick and Palomar observatories.{{cite journal

|last=Vorontsov-Vel'Iaminov

|first=B. A.

|authorlink=Boris Vorontsov-Velyaminov

|year=1958

|title=The interaction of galaxies and the nature of their arms, spanning filaments and tails. The morphology of galaxies. V

|journal=Astronomicheskii Zhurnal

|volume=35

|pages=858

|bibcode=1958AZh....35..858V

}}