Proper absorber separation from a wavelength interval
= Proper absorber separation from a wavelength interval
{title2=$\ell\simeq c\Delta\lambda/[H(z)(1+z)\lambda_{\rm rest}]$}
A local redshift spacing between absorbers corresponds to proper path length $c\Delta z/[H(z)(1+z)]$. Using the same rest-frame transition for all lines gives $\Delta z=\Delta\lambda/\lambda_{\rm rest}$. This conversion assumes <cosmological redshift> dominates the line spacing and uses a local Hubble-rate approximation.