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Galaxy effective radius

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Half light radius Re encloses half of the total light emitted by an object

Galaxy effective radius or half-light radius () is the radius at which half of the total light of a galaxy is emitted.[1][2] This assumes the galaxy has either intrinsic spherical symmetry or is at least circularly symmetric as viewed in the plane of the sky. Alternatively, a half-light contour, or isophote, may be used for spherically and circularly asymmetric objects.

is an important length scale in term in de Vaucouleurs law,[3] which characterizes a specific rate at which surface brightness decreases as a function of radius: where is the surface brightness at . At ,

Thus, the central surface brightness is approximately .

See also

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References

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  1. ^ "Half-light Radius". Swinburne University. Retrieved 22 May 2013.
  2. ^ Binney, James; Tremaine, Scott (2008). Galactic Dynamics (Second ed.). Princeton Series in Astrophysics. p. 21. ISBN 9780691130279.
  3. ^ Mazure, Alain (15 February 2002). "Exact solutions for the spatial de Vaucouleurs and Sérsic laws and related quantities" (PDF). Astronomy & Astrophysics. 383 (2): 384–389. arXiv:astro-ph/0112147. Bibcode:2002A&A...383..384M. doi:10.1051/0004-6361:20011751. S2CID 17651247.