Tuesday, 9 December 2014

cosmology - How to find the distance between two quasars

I want to calculate the distance between two quasars of which I know the angular position and the red shift. Let $Q_1=(alpha_1,delta_1, z_1)$ and $Q_2=(alpha 2,delta 2, z_2)$ and suppose $z_2 > z_1$.



I know how to find the angular separation $theta$ between them by means of the angular coordinates. But how to find the comoving distance (at epoch $z=0$) from them ? I know how to find the comoving distance from the Earth of the two quasars, can we find the distance between them using these two distances?



A related question is to find the redshift of $Q_2$ as seen by $Q_1$ at the epoch when $Q_1$ received the light emitted from $Q_2$ .



There is some standard method to solve this problem ?

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