# Galaxies and projected radius vs arcmins

I have two sets of data (globular clusters), one for the Andromeda Galaxy and one for the Milky Way.

I want to compare the distribution of globular clusters between the two galaxies according to their distance from the galaxy's centre, but the measurements they use in each are different.

Andromeda has $(X,Y)$ locations for the GCs in arcminutes, with $R = \sqrt{X^2 + Y^2}$

The MW data has $(X,Y)$ locations in kpc from the galactic centre. It also has a value for $R_{\rm gc}$ (distance from galactic centre) in kpc.

What's the easiest way to convert one of these sets so I can compare the two populations?

I would suspect it would be easier to convert the Milky Way data into arcminutes. I am aware of a way to get $R_{\rm projected}$ values, $R_{\rm projected} = (\pi/4)R_{\rm gc}$ but I'm not sure if that's what I need to do. Or is there something else I should be looking at?

• Hmmm, this is going well. Any thoughts, or could I rephrase the question perhaps? – Carl May 25 '12 at 9:16