Polar-ring galaxy

NGC 660 showing polar-galaxy structure

A polar-ring galaxy is a type of galaxy with an outer ring of gas and stars that rotates over the poles of the galaxy.[1] These polar rings are thought to form when two galaxies gravitationally interact with each other. One possibility is that a material is tidally stripped from a passing galaxy to produce the polar ring.[2] The other possibility is that a smaller galaxy collides orthogonally with the plane of rotation of the larger galaxy, with the smaller galaxy effectively forming the polar-ring structure.[3]

The best-known polar-ring galaxies are S0s (lenticular galaxies), but from the physical point of view they are part of a wider category of galaxies, including several ellipticals.

The first four S0 galaxies that were identified as polar-ring galaxies were NGC 2685,[4] NGC 4650A,[5][6] A 0136 -0801,[3] and ESO 415 -G26.[6] While these galaxies have been extensively studied, many other polar-ring galaxies have since been identified.[7] Polar-ring S0 galaxies may be found around 0.5% of all nearby lenticular galaxies, and it is possible that 5% of lenticular galaxies may have had polar rings at some point during their lifetimes.[7]

The first polar-ring elliptical galaxies were identified in 1978. They were NGC 5128, NGC 5363, NGC 1947 and Cygnus A,[8] while the polar-ring S0 galaxies NGC 2685 and NGC 4650A were at that time indicated as resulting from similar formation processes.[8] Only some years later, when the first observations of the stellar and gas motion of polar-ring elliptical and S0 galaxies were possible with a better spectroscopic technology, the external origin of the gaseous rings was clarified.[3][6][9][10] In addition to the best-known example, NGC 5128 (Cen A), a very regular polar ring elliptical, is NGC 5266.[10]

  1. ^ James Binney; Michael Merrifield (1998). Galactic Astronomy. Princeton, New Jersey: Princeton University Press. ISBN 0-691-00402-1.
  2. ^ Ristea, Andrei (2023). "The SAMI Galaxy Survey: physical drivers of stellar-gas kinematic misalignments in the nearby Universe". Monthly Notices of the Royal Astronomical Society. 517 (2): 2677. arXiv:2210.01147. doi:10.1093/mnras/stac2839.
  3. ^ a b c F. Schweizer; B. C. Whitmore; V. C. Rubin (1983). "Colliding and merging galaxies. II - S0 galaxies with polar rings". Astronomical Journal. 88: 909–925. Bibcode:1983AJ.....88..909S. doi:10.1086/113377.
  4. ^ P. L. Schecter; J. E. Gunn (1978). "NGC 2685 - Spindle or pancake". Astronomical Journal. 83: 1360–1362. Bibcode:1978AJ.....83.1360S. doi:10.1086/112324.
  5. ^ J. L. Sérsic (1967). "Southern Peculiar Galaxies III". Zeitschrift für Astrophysik. 67: 306–311. Bibcode:1967ZA.....67..306S.
  6. ^ a b c B. C. Whitmore; D. B. McElroy; F. Schweizer (1987). "The shape of the dark halo in polar-ring galaxies". Astrophysical Journal. 314: 439–456. Bibcode:1987ApJ...314..439W. doi:10.1086/165077.
  7. ^ a b B. C. Whitmore; R. A. Lucas; D. B. McElroy; T. Y. Steiman-Cameron; P. D. Sackett; R. P. Olling (1990). "New observations and a photographic atlas of polar-ring galaxies". Astronomical Journal. 100: 1489–1522, 1721–1755. Bibcode:1990AJ....100.1489W. doi:10.1086/115614.
  8. ^ a b Bertola, F. & Galletta, G. (1978). "A new type of galaxy with prolate structure". Astrophysical Journal. 226: L115–L118. Bibcode:1978ApJ...226L.115B. doi:10.1086/182844.,
  9. ^ Bertola, F.; Galletta, G.; Zeilinger, W.~W. (1985). "Warped dust lanes in elliptical galaxies - Transient or stationary phenomena?". Astrophysical Journal. 292: L51–L55. Bibcode:1985ApJ...292L..51B. doi:10.1086/184471.
  10. ^ a b Varnas, S.R. Bertola; F., Galletta; G., Freeman; K.C., Carter, D. (1987). "NGC 5266 - an elliptical galaxy with a dust ring". Astrophysical Journal. 313: 69–88. Bibcode:1987ApJ...313...69V. doi:10.1086/164949.{{cite journal}}: CS1 maint: multiple names: authors list (link)