Introduction to Cosmology Example Exam Question: Hints

Lecture 11: Hubble's Law, part 2

Describe carefully any two of the following Cepheid-calibrated extragalactic distance indicators. Your account should explain the basis of the technique and how it is used to measure distance. Mention any particular advantages or disadvantages.
Note that this is not the same question as the similar-looking one in problems and homework 4! Here you are being asked to go into significant detail – 5 marks is 10% of the exam, so 10–15 minutes' work. Also note that you are asked to consider only two out of the three choices on offer. Should you attempt all three, you will be credited with the best two (so, if you were to get 3/5, 2/5 and 2/5, your total mark would be 5/10). It is not efficient to do this unless (a) you have spare time and (b) you are genuinely not sure which two you understand best.
(i) The Fundamental Plane;	[5]
The basic questions you should ask yourself for each of these titles are: What is the basis of the method, i.e. what properties of the target object do you measure, and how do you deduce the distance? (This will also tell you whether it is a luminosity distance or an angular size distance.) What are the target objects, i.e. what type of star/galaxy/cluster is being observed? How is the method calibrated? Are there any significant systematic errors or model dependences involved? What are the advantages and disadvantages of the technique?
(ii) Type II supernovae;	[5]
(iii) Gravitational Lens time delays.	[5]

(2005 Q5(b) [slightly modified].)