{{short description|Elongated structure composed of stars and gas that extends from a galaxy}} [[File:UGC 10214HST.jpg|right|thumb|The Tadpole Galaxy, image taken by the Hubble Space Telescope's ACS.]]
'''A tidal tail''' is a thin, elongated region of stars and interstellar gas that extends into space from a galaxy. Tidal tails occur as a result of galactic tide forces between interacting galaxies. Examples of galaxies with tidal tails include the Tadpole Galaxy and the Mice Galaxies. Tidal forces can eject a significant amount of a galaxy's gas into the tail; within the Antennae Galaxies, for example, nearly half of the observed gaseous matter is found within the tail structures.<ref>{{cite journal | doi = 10.1086/173373 | title = Modeling the Spatial Distribution of Star Formation in Interacting Disk Galaxies | journal = Astrophysical Journal | volume = 418 | pages = 82–99 | date = 1993 | author = Mihos, Christopher J. | display-authors = etal | bibcode = 1993ApJ...418...82M }}</ref>
== History == The phenomena now referred to as tidal tails were first studied extensively by Fritz Zwicky in 1953.<ref>{{cite journal | title = Luminous and dark formations of intergalactic matter | author = Zwicky, Fritz | journal = Physics Today | date = April 1953 | volume = 6 | issue = 4 | pages = 7–11 | doi = 10.1063/1.3061224|bibcode = 1953PhT.....6....7Z }}</ref> Several astrophysicists expressed their doubts that these extensions could occur solely as the result of tidal forces,<ref>{{cite journal | title = The Possibility of a Long Lifetime for Intergalactic Arms | author = Zasov, A. V. | journal = Soviet Astronomy | volume = 11 | issue = 5 | pages = 785 | date = 1968 | bibcode = 1968SvA....11..785Z}}</ref><ref>{{cite conference | title = Cosmic rays and radio waves as manifestations of a hot universe | author = Gold, T. | author2 = Hoyle, F. | name-list-style = amp | book-title = Paris Symposium on Radio Astronomy | publisher = Stanford University Press | pages = 583–588 | url = https://books.google.com/books?id=g56aAAAAIAAJ&pg=PA583| date = 1959}}</ref> including Zwicky himself, who described his own views as "unorthodox".<ref>{{cite journal | author = Zwicky, Fritz | title = Intergalactic Bridges | journal = Astronomical Society of the Pacific Leaflets | volume = 9 | issue = 403 | pages = 17–24 | date = 1963 | bibcode = 1963ASPL....9...17Z}}</ref> Boris Vorontsov-Velyaminov argued that the tails were too thin and too long to have been produced by gravity alone,<ref>{{cite conference | title = Interaction of Multiple Systems | author = Vorontsov-Velyaminov, B. | book-title = Problems of Extra-Galactic Research | date = 1962 | publisher = Macmillan Press | pages = 194–200 | url = https://adsabs.harvard.edu/full/1962IAUS...15..194V | bibcode = 1962IAUS...15..194V }}</ref> as gravity should instead produce broad distortions. However, in 1972, renowned astronomer Alar Toomre modeled close encounters of disk galaxies using three-body (test-particle) simulations and proved that tidal perturbations produce tail structures in interacting systems. that it was indeed tidal forces that were responsible for the tails.<ref name=":3">{{cite journal | title = Galactic Bridges and Tails | journal = Astrophysical Journal | volume = 178 | pages = 623–666 | date = 15 December 1972 | author = Toomre, Alan | author2 = Toomre, Juri | name-list-style = amp | doi = 10.1086/151823 | bibcode=1972ApJ...178..623T}}</ref>
== Structure ==
=== Morphology === When galaxies interact, the uneven tidal forces between the galaxies can pull matter away from the galactic disks forming tidal tails.<ref name=":3" /> Galaxy surveys have found the longest tidal tails can extend farther than 100 kpc from a galaxy, however, most tidal tails surveyed were 10-20 kpc.<ref>{{Cite journal|last1=Mohamed |first1=Y. H. |last2=Reshetnikov |first2=V. P. |last3=Sotnikova |first3=N. Ya |title=On the characteristics of tidal structures of interacting galaxies |journal=Astronomy Letters |date=2011 |volume=37 |issue=10 |pages=670–678 |doi=10.1134/S1063773711100045 |language=en |arxiv=1108.6155v1 |bibcode=2011AstL...37..670M }}</ref> The shapes of tidal tails can be fit into three broad categories: straight, curved, and plume (formed by the dispersion of tail materials that have gravitated back to the galaxy).<ref>{{Cite journal |last1=Ren |first1=Jian |last2=Zheng |first2=X Z |last3=Valls-Gabaud |first3=David |last4=Duc |first4=Pierre-Alain |last5=Bell |first5=Eric F |last6=Pan |first6=Zhizheng |last7=Qin |first7=Jianbo |last8=Shi |first8=D D |last9=Qiao |first9=Man |last10=He |first10=Yongqiang |last11=Wen |first11=Run |date=2020-10-29 |title=Long tidal tails in merging galaxies and their implications |url=https://academic.oup.com/mnras/article/499/3/3399/5937491 |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=499 |issue=3 |pages=3399–3409 |doi=10.1093/mnras/staa2985 |doi-access=free |issn=0035-8711|arxiv=2009.11879 }}</ref>
The structure of tidal tails depends on the geometry of encountered galaxies.<ref>{{Cite journal |last1=Toomre |first1=Alar |last2=Toomre |first2=Juri |title=1972ApJ...178..623T Page 623 |url=https://adsabs.harvard.edu/full/1972ApJ...178..623T |access-date=2026-02-18 |journal=The Astrophysical Journal |date=1972 |volume=178 |page=623 |doi=10.1086/151823 |bibcode=1972ApJ...178..623T }}</ref> When the spin of a galactic disk is aligned with the direction of orbital motion, interactions usually generate long and prominent tidal tails. When the disk rotation opposes the orbital motion, tidal features tend to be weaker.<ref>{{Cite journal |last1=Rudnick |first1=Gregory |last2=Rix |first2=Hans-Walter |date=September 1998 |title=Lopsidedness in Early-Type Disk Galaxies |journal=The Astronomical Journal |volume=116 |issue=3 |pages=1163–1168 |doi=10.1086/300518 |arxiv=astro-ph/9805316 |bibcode=1998AJ....116.1163R |issn=0004-6256}}</ref> Some interacting galaxy pairs have two distinct tails, as is the case for the Antennae Galaxies, while other systems have only one tail. The mass ratio between the interacting galaxies can influence how many tidal tails form and how symmetric they appear.<ref>{{cite journal|last1=Duc |first1=Pierre-Alain |title=Tidal dwarf galaxies |date=1997-11-21 |last2=Mirabel |first2=Felix |journal=The Messenger |volume=89 |page=14 |arxiv=astro-ph/9711253 |bibcode=1997Msngr..89...14D }}</ref> Gravitational torques transmitting during close passages transfer angular momentum outward, making material from the outer disk to move far from the center of the galaxy.<ref>{{cite arXiv|last=Bournaud |first=Frederic |title=Star formation and structure formation in galaxy collisions |date=2009-09-16 |class=astro-ph.CO |eprint=0909.1812 }}</ref>
=== Gas content === Tidal tails (and other tidal features) are found to have a gas content primarily composed of atomic hydrogen (HI),<ref name=":4">{{cite arXiv|last=Combes |first=F. |title=Extended gas in interacting systems |date=1997-11-03 |eprint=astro-ph/9711006 }}</ref> however, regions of molecular hydrogen (H<sub>2</sub>), traced by CO, are sometimes found in areas of proportionally high densities of HI.<ref>{{Cite journal |last1=Braine |first1=Jonathan |last2=Lisenfeld |first2=Ute |last3=Due |first3=Pierre-Alain |last4=Leon |first4=Stéphane |date=2000-02-24 |title=Formation of molecular gas in the tidal debris of violent galaxy–galaxy interactions |url=https://www.nature.com/articles/35002521 |journal=Nature |language=en |volume=403 |issue=6772 |pages=867–869 |doi=10.1038/35002521 |pmid=10706277 |bibcode=2000Natur.403..867B |issn=1476-4687|url-access=subscription }}</ref> Additionally, it is found that tidal tails tend to have low metallicity and dust content, which decrease exponentially at increasing distances from the galaxy.<ref name=":4" />
=== Stellar composition === Along with the stars pulled out or created by tidal effects, tidal tails have also been found to have active star forming regions with similar properties to those found in galactic disks.<ref name=":5">{{Cite journal |last1=Rodruck |first1=Michael |last2=Charlton |first2=Jane |last3=Borthakur |first3=Sanchayeeta |last4=Chitre |first4=Aparna |last5=Durrell |first5=Patrick R |last6=Elmegreen |first6=Debra |last7=English |first7=Jayanne |last8=Gallagher |first8=Sarah C |last9=Gronwall |first9=Caryl |last10=Knierman |first10=Karen |last11=Konstantopoulos |first11=Iraklis |last12=Li |first12=Yuexing |last13=Maji |first13=Moupiya |last14=Mullan |first14=Brendan |last15=Trancho |first15=Gelys |date=2023-09-29 |title=Star clusters in tidal debris |url=https://academic.oup.com/mnras/article/526/2/2341/7286662 |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=526 |issue=2 |pages=2341–2364 |doi=10.1093/mnras/stad2886 |doi-access=free |issn=0035-8711}}</ref> Star clusters, including active regions, can be generally found throughout the whole length of the tail.<ref name=":5" /> In galaxies with tidal tails, the tails harbor approximately 10% of the galaxy's stellar formation.<ref>{{cite journal | title = Remarkable Disk and Off-Nuclear Starburst Activity in the Tadpole Galaxy as revealed by the Spitzer Space Telescope | author = Jarrett, T. H. | display-authors = etal | journal = Astronomical Journal | volume = 131 | issue = 1 | pages = 261–281 | date = 2006 | doi = 10.1086/498414 | bibcode=2006AJ....131..261J|arxiv = astro-ph/0510788 }}</ref> Overall, roughly 1% of all stellar formation in the known universe occurs within tidal tails.<ref>{{cite web | title = 'Shot in the Dark' Star Explosion Stuns Astronomers | url = http://www.nasa.gov/centers/goddard/news/topstory/2007/intergalatic_shot.html | publisher = NASA Goddard Flight Center | date = 18 December 2007 | author = Naeye, Robert | access-date = 18 June 2010}}</ref>
== Observational properties ==
Most images show that many nearby disk galaxies host extended and faint tidal structures.<ref>{{Cite journal |last=Martínez-Delgado |first=David |last2=Gabany |first2=R. Jay |last3=Crawford |first3=Ken |last4=Zibetti |first4=Stefano |last5=Majewski |first5=Steven R. |last6=Rix |first6=Hans-Walter |last7=Fliri |first7=Jürgen |last8=Carballo-Bello |first8=Julio A. |last9=Bardalez-Gagliuffi |first9=Daniella C. |last10=Peñarrubia |first10=Jorge |last11=Chonis |first11=Taylor S. |last12=Madore |first12=Barry |last13=Trujillo |first13=Ignacio |last14=Schirmer |first14=Mischa |last15=McDavid |first15=David A. |date=2010-09-07 |title=STELLAR TIDAL STREAMS IN SPIRAL GALAXIES OF THE LOCAL VOLUME: A PILOT SURVEY WITH MODEST APERTURE TELESCOPES |journal=The Astronomical Journal |volume=140 |issue=4 |pages=962–967 |doi=10.1088/0004-6256/140/4/962 |issn=0004-6256|arxiv=1003.4860 }}</ref> Identifying the tidal tails can be limited by background modelling and imaging artifacts in data.<ref>{{Cite journal |last=Sola |first=Elisabeth |last2=Duc |first2=Pierre-Alain |last3=Richards |first3=Felix |last4=Paiement |first4=Adeline |last5=Urbano |first5=Mathias |last6=Klehammer |first6=Julie |last7=Bílek |first7=Michal |last8=Cuillandre |first8=Jean-Charles |last9=Gwyn |first9=Stephen |last10=McConnachie |first10=Alan |date=2022-06-01 |title=Characterization of low surface brightness structures in annotated deep images |url=https://www.aanda.org/articles/aa/abs/2022/06/aa42675-21/aa42675-21.html |journal=Astronomy & Astrophysics |language=en |volume=662 |pages=A124 |doi=10.1051/0004-6361/202142675 |issn=0004-6361|arxiv=2203.03973 }}</ref> Tidal tails are a common outcome of gravitational interactions between disk galaxies.<ref>{{Cite journal |last=Barnes |first=Joshua E. |last2=Hernquist |first2=Lars |date=1992-09-01 |title=Dynamics of Interacting Galaxies |url=https://www.annualreviews.org/content/journals/10.1146/annurev.aa.30.090192.003421 |journal=Annual Review of Astronomy and Astrophysics |language=en |volume=30 |issue= |pages=705–742 |doi=10.1146/annurev.aa.30.090192.003421 |issn=0066-4146|url-access=subscription }}</ref> Neutral hydrogen can trace tidal debris farther out than the optical light.<ref>{{Cite journal |last=Hibbard |first=J. E. |last2=van Gorkom |first2=J. H. |date= |title=HI, HII, and R-Band Observations of a Galactic Merger Sequence |url=https://ui.adsabs.harvard.edu/abs/1996AJ....111..655H/abstract |journal=The Astronomical Journal |language=en |volume=111 |pages=655 |doi=10.1086/117815 |issn=0004-6256|arxiv=astro-ph/9512035 }}</ref> Star-forming condensations in tidal debris can tend to be tidal dwarf galaxies during the approach.<ref>{{Cite journal |last=Barnes |first=Joshua E. |last2=Hernquist |first2=Lars |date=1992-09-01 |title=Dynamics of Interacting Galaxies |url=https://www.annualreviews.org/content/journals/10.1146/annurev.aa.30.090192.003421 |journal=Annual Review of Astronomy and Astrophysics |language=en |volume=30 |issue= |pages=705–742 |doi=10.1146/annurev.aa.30.090192.003421 |issn=0066-4146|url-access=subscription }}</ref>
== Tidal tails of clusters == Tidal tails have been observed in clusters as well as galaxies. There have been tidal tails identified around NGC 5466.<ref name=":0">{{Cite journal |last=Dietrich |first=J. P. |date=February 2008 |title=The Importance of Being First: Position Dependent Citation Rates on arXiv:astro-ph |url=https://doi.org/10.1086/527522 |journal=Publications of the Astronomical Society of the Pacific |volume=120 |issue=864 |pages=224–228 |doi=10.1086/527522 |arxiv=0712.1037 |bibcode=2008PASP..120..224D |issn=0004-6280}}</ref> These tails appear to be roughly 4 degrees in the sky, or 1 kpc in length.<ref name=":0" /> There have been other clusters observed with tidal tails as well,<ref>{{Cite journal |last1=Piatti |first1=Andrés E. |last2=Carballo-Bello |first2=Julio A. |date=2020-05-01 |title=The tidal tails of Milky Way globular clusters |url=https://www.aanda.org/articles/aa/full_html/2020/05/aa37994-20/aa37994-20.html#:~:text=The%20formation%20of%20stellar%20streams,2004). |journal=Astronomy & Astrophysics |language=en |volume=637 |pages=L2 |doi=10.1051/0004-6361/202037994 |arxiv=2004.11747 |bibcode=2020A&A...637L...2P |issn=0004-6361}}</ref><ref>{{Cite journal |last1=Zhang |first1=Jiajun |last2=Zhao |first2=Jingkun |last3=Oswalt |first3=Terry D. |last4=Fang |first4=Xiangsong |last5=Zhao |first5=Gang |last6=Liang |first6=Xilong |last7=Ye |first7=Xianhao |last8=Zhong |first8=Jing |date=2019-12-12 |title=Stellar Chromospheric Activity and Age Relation from Open Clusters in the LAMOST Survey |journal=The Astrophysical Journal |volume=887 |issue=1 |pages=84 |arxiv=1909.13520 |bibcode=2019ApJ...887...84Z |doi=10.3847/1538-4357/ab4efe |issn=0004-637X |doi-access=free}}</ref>
* NGC 2516, from tip of leading tail to tip of trailing tail, 380 pc.<ref name=":1">{{cite journal |arxiv=2406.18767 |doi=10.1051/0004-6361/202449828 |title=Tidal tails of open clusters |date=2024 |last1=Kos |first1=Janez |journal=Astronomy & Astrophysics |volume=691 |pages=A28 |bibcode=2024A&A...691A..28K }}</ref> * Theia 456 (COIN-Gaia 13), tidal tail spans 200 pc.<ref name=":1" /> * NGC 752, estimates are less than 1.5 kpc to several kpc.<ref name=":1" /> *ASCC 101, trailing tail is 100 pc, leading tail is hard to measure due to its position.<ref name=":2">{{cite journal |arxiv=2501.17225 |last1=Risbud |first1=Dhanraj |last2=Jadhav |first2=Vikrant V. |last3=Kroupa |first3=Pavel |title=Tidal tails of nearby open clusters I. Mapping with Gaia DR3 |journal=Astronomy and Astrophysics |date=2025 |volume=694 |doi=10.1051/0004-6361/202453302 |bibcode=2025A&A...694A.258R }}</ref> *Alessi 3, leading tail 120 pc, trailing tail 60 pc.<ref name=":2" /> *Blanco 1, both tails extend approximately 50-60 pc.<ref name=":2" /> *Collinder 350, both tails extend approximately 50pc.<ref name=":2" /> *Melotte 111, both tails span 50 pc.<ref name=":2" /> *Melotte 25, leading tail is 70 pc, trailing tail is 70 pc.<ref name=":2" /> *Roslund 6, both tails extend approximately 100 pc.<ref name=":2" /> *Theia 517, leading tail is 120 pc and trailing tail is 150 pc.<ref name=":2" /> These tidal tails are difficult to measure and different studies show different results. We can most accurately measure tidal tails close to Earth and in the correct orientation.
== Gallery == <gallery> Galaxy with an ejected supermassive black hole.jpg|Arc-shaped tidal tails in galaxy 3C186.<ref>{{cite news|title=Hubble detects supermassive black hole kicked out of galactic core - Astronomers suspect gravitational waves|url=https://www.spacetelescope.org/news/heic1706/|access-date=27 March 2017|work=www.spacetelescope.org}}</ref> </gallery>
== Notes == {{reflist}}
*