# Calculating a rotation curve

1. Mar 3, 2015

### zaq

I hope this is in the right forum.
I'm trying to see how to calculate rotation curves for a spiral galaxy.
The data I have is brightness profile (mag/arcsec^2) and observed rotation curve - to see how it fits.
from what I found I need the total mass, and for that I need the surface mass density.
I couldn't find how to convert the brightness profile to mass density.
I can probably let matlab integrate the spline of the brightness profile, but that's not the mass density, so it wouldn't give me the mass I need.

Would appreciate help.
References to books (preferably with solved exercises) or other material are very welcome.

zaq

2. Mar 7, 2015

3. Mar 8, 2015

### zaq

no, but thanks for trying.
I think I need to clarify what I'm asking.
The steps I found for calculating an RC are:
get the intensity profile
use that to find the mass distribution
use mass distribution to find g
calculate rotation curve.

I have the luminosity profile. (\mu). The units are mag/pc^2.
I need to convert it to mass distribution \SIGMA r (M/ pc^2).
how do I do that? I know I'm suppose to assume mass to light ratio but how exactly?