A very elementary question, just to make sure I got this thing right.
Suppose we are given that the mass to luminosity ratio of a galaxy is $2 \frac{M_{\odot}}{L_{\odot}}$.

Let us say, that the luminosity of the galaxy = $L = 100\,L_{\odot}/pc^2$.

Then the mass density of the galaxy = $\rho = 100 L_{\odot}/pc^2 \times 2 \frac{M_{\odot}}{L_{\odot}} = 200 M_{\odot}/pc^2$.

Is this the right calculation?

  • 1
    $\begingroup$ The mass surface density. $\endgroup$
    – ProfRob
    Commented Oct 3, 2023 at 16:58


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