Friday, January 27, 2012

redshift space

what's the finger-of-god-effect and the Kaiser-effect in galaxy surveys?

1 comment:

  1. both effects are redshift-space distortions, that means one does not observe galaxies at their true cosmological redshifts but sees the galaxies displaced because of a kinematical redshift superimposed due to peculiar motion. The finger-of-god effect is an elongation of a relaxed system of galaxies with isotropic random velocities of which we just see the los-component, i.e. a random Doppler-redshift added to the cosmological redshift, which elongates the distribution of galaxies in redshift. The Kaiser effect concerns the spherically symmetric accretion of galaxies onto a large structure. Galaxies behind a structure move towards it and towards the observer, such that the cosmological redshift is decreased, and galaxies in front of a structure are moving towards it and away from the observer, such that the cosmological redshift is increased, leading to a flattening in redshift of the galaxies being accreted.

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