K correction

K correction is a correction to an astronomical object's magnitude (or equivalently, its flux) that allows a measurement of a quantity of light from an object at a redshift z to be converted to an equivalent measurement in the rest frame of the object. If one could measure all the light from an object at all wavelengths (a bolometric flux), a K correction would not be required. If one measures the light emitted in an emission line, a K-correction is not required. The need for a K-correction arises because an astronomical measurement through a single filter or a single bandpass only sees a fraction of the total spectrum, redshifted into the frame of the observer. So if the observer wants to compare the measurements through a red filter of objects at different redshifts, the observer will have to apply estimates of the K corrections to these measurements to make a comparison.

One claim for the origin of the term "K correction" is Edwin Hubble, who supposedly arbitrarily chose K to represent the reduction factor in magnitude due to this effect.[1] Yet Kinney et al., in footnote 7 on page 48 of their article,[2] note an earlier origin from Carl Wilhelm Wirtz (1918),[3] who referred to the correction as a Konstante (German for "constant"), hence K-correction.

The exact nature of the calculation that needs to be applied in order to perform a K correction depends upon the type of filter used to make the observation and the shape of the object's spectrum. If multi-color photometric measurements are available for a given object thus defining its spectral energy distribution (SED), K corrections then can be computed by fitting it against a theoretical or empirical SED template.[4] It has been shown, that K corrections in many frequently used broad-band filters for low-redshift galaxies can be precisely approximated using two-dimensional polynomials as functions of a redshift and one observed color.[5] This approach is implemented in the K corrections calculator web-service.[6]

References

  1. ^ Hubble, Edwin (1936). "Effects of Red Shifts on the Distribution of Nebulae". Astrophysical Journal 84: 517–554. Bibcode 1936ApJ....84..517H. doi:10.1086/143782. 
  2. ^ Kinney et al., A.C.; Calzetti, Daniela; Bohlin, Ralph C.; McQuade, Kerry; Storchi-Bergmann, Thaisa; Schmitt, Henrique R. (1996). "Template ultraviolet spectra to near-infrared spectra of star-forming galaxies and their application to K-corrections". Astrophysical Journal 467: 38–60. Bibcode 1996ApJ...467...38K. doi:10.1086/177583. 
  3. ^ Wirtz, V.C. (1918). "Über die Bewegungen der Nebelflecke". Astronomische Nachrichten 206 (13): 109. doi:10.1002/asna.19182061302. 
  4. ^ K-corrections and filter transformations in the ultraviolet, optical, and near infrared
  5. ^ Analytical approximations of K-corrections in optical and near-infrared bands
  6. ^ K-corrections calculator

External links