Quote:
Originally Posted by Robh
Given that the degree of lensing will be both a function of the mass and the expansion of space, how on Earth do you differentiate between the two? I would have thought that the mass of the dark matter would be estimated from the lensing but if this has an expansion component then the mass estimate is going to be somewhat unknown. Do we know enough about the visual galaxy components of Abell 1689 (e.g. relative motions) to estimate the mass of the dark matter?
Regards, Rob.
|
It's a matter of geometry. You model what the lensing effect will be with matter + dark matter alone and then overlay that with the observed lensing effects. Any difference that can't be accounted for by either the modeled lens and the variations due to uncertainties in the modeled values would then be most likely due to the expansion of spacetime being generated by dark energy. However, as you have pointed out, it's predicated on having a good handle of the mass/DM distribution and relative motions of the galaxy in the cluster.