# I How to extract dark matter mass from a hydrostatic study

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1. Dec 1, 2016

### Jules Winnfield

In 2005, A. Vikhlinin et al. made a hydrostatic equilibrium study - https://arxiv.org/abs/astro-ph/0507092 - of some dozen galaxy clusters. These hydrostatic studies are useful because they don't contain the M/L assumptions of other methods. From this document, I'm trying to extract the dark matter mass of the cluster. Is it safe to assume that the dark matter mass is the total mass less the gas fraction ($M_{500}$ - $M_{500}$ * $F_{g,500}$)?

Or is there another way to extract an unambiguous value of dark matter from the concentration parameter that I've not yet found? In table 4, he lists the concentration parameter, but doesn't list the central density. Am I missing something?

2. Dec 2, 2016

### Jules Winnfield

The author responded to my query. The formula above is the right way to extract the dark matter mass. He added that the stellar mass is about $\frac{1}{10}$ percent of the gas mass, so if I wanted to be even more accurate, I could subtract that also.

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