are distortions (stretching and flattening) of the galaxy (2D) two-point correlation function
, and also power spectrum
(which have to be spherically symmetric in isotropic Universe) caused by peculiar (non-Hubble) motions of galaxies. These distortions can be divided onto:
- Finger of God effect — stretching of (or flattening of ) along the line of sight on non-linear (less then Mpc) scales due to random velocities of galaxies (e.g. virial velocities inside clusters), as far as redshift measurement errors;
- Kaiser effect (or -distortion) — flattening of (or stretching of ) along the line of sight on linear (more then ) due to the galaxies infall onto overdense regions.
There is also one more effect causing the distortions of
even in the real space
— the so called geometric flattening