Past exam of the astrophysics course of the University of Oxford / 2015 / 8 / f / ii

For a small radial comoving interval, $d{D}_C/dz=c/H(z)$. At $z=2$,ThusThis uses the unbound cosmological radial separation between separate quasars, unlike the peculiar-velocity redshift dispersion of galaxies inside the bound group. Integrating the distance relation instead of linearizing gives a small correction for a specified direction and endpoint. The quoted characteristic spacing alone does not assert that the same nearest object lies both purely transverse and purely radial.