# Astrophysics Redshift Question

stuartgriffin
Homework Statement:
A galaxy cluster of mass 3.0 × 1013M⊙ with known distance of 20 Mpc is observed in the centre of a bright ring, which is presumably a lensed galaxy. The angular radius of the ring from the cluster is 1.13 arcmin. The ring is observed to have a redshift of 0.0075. Assuming a value of 70kms−1Mpc−1 for the Hubble constant, determine whether the ring’s redshift distance is consistent at an accuracy of ~5% to the distance expected for the lensed galaxy to actually be located directly behind the cluster.
Relevant Equations:
a=4GM/bc^2
V=H0D
I have attempted to link the equations, but I don't really understand how the data given fits. Does the angular radius get plugged in as the deflection angle?

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What is the distance to the lensed galaxy? How can this help you get the deflection angle?

• stuartgriffin
stuartgriffin
What is the distance to the lensed galaxy? How can this help you get the deflection angle?

Ahhh, thank you, so I calculate the distance using the redshift and hubbles constant? Am I on the right lines with the equations I am using?

stuartgriffin
What is the distance to the lensed galaxy? How can this help you get the deflection angle?
Does this look like I'm headed on the right track?

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