# A How to convert between different mass measurements for CDM H

1. Jul 6, 2016

### floyd0117

If I have a cluster with a mass measured in M_500c, then how do I go about converting that mass to M_200c given some concentration and an NFW profile?

2. Jul 6, 2016

### Chalnoth

What do you mean converting the mass? What are you converting? Why?

3. Jul 7, 2016

### floyd0117

I have a dataset of cluster masses, expressed in units of M_500c, which I need to relate to a velocity dispersion. But the relation between cluster mass and velocity dispersion is in terms of M_200c, so I need to convert the masses in the dataset before I can find the equivalent dispersions.

4. Jul 7, 2016

### Chalnoth

Ahh, okay. I'm honestly not sure. I did find this resource, which describes these measures a bit:

It looks like $M_{500}$ is the mass within $R_{500}$, while $M_{200}$ is the mass within $R_{200}$, where $R_{500} \approx 0.7 R_{200}$. If you've got a good understanding of the NFW profile, you might be able to use that to do the conversion.

That said, my guess is it'd be even better to convert the relation between mass and dispersion to be in terms of $M_{500}$ instead of $M_{200}$, as that's most likely a far simpler operation.

Last edited by a moderator: May 8, 2017
5. Jul 7, 2016

### floyd0117

Perhaps, but I'm trying to follow the methodology presented in a specific paper and replicate their results. Thanks anyway

Last edited by a moderator: May 8, 2017
6. Jul 7, 2016

### Chalnoth

Makes sense. Sorry I can't be of more help.