9
$\begingroup$

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 ?

$\endgroup$
5
$\begingroup$

Edit: I found you a very relevant paper!

http://arxiv.org/pdf/astro-ph/0007341v1.pdf seems to be solving exactly your problems for sources with arbitrary angular separation $\alpha$. Equations (12) and (14) will give you the comoving distance $\chi_2'$ and redshift $z_2'$ between them at the epoch when $Q_1$ received light from $Q_2$. You will have to solve these equations numerically to find the solutions, which will be more complicated depending on the cosmological model you use.


Have a read of these notes http://arxiv.org/abs/astro-ph/9905116. They are my go-to when trying to work out cosmological distances.

$\endgroup$
  • $\begingroup$ This is what we consider a link-only answer. While it may be helpful, a summary of the information found there is a good idea to include. $\endgroup$ – Hohmannfan Apr 27 '16 at 8:20
  • 1
    $\begingroup$ Thanks, I've edited with more information about another source $\endgroup$ – cnosam Apr 27 '16 at 18:04
  • 1
    $\begingroup$ That is better. Welcome to Astronomy SE! $\endgroup$ – Hohmannfan Apr 27 '16 at 18:26

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.