Dark Matter and Gas in Clusters of Galaxies

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Some brief explanations

• For a spherical cluster of galaxies we show the distribution of dark matter and hot intracluster gas (ICM), and their properties: density, mass inside radius r, the speeds of circular orbits and for escape from radius r, and the maximum ram pressure that would be experienced by a galaxy when it comes as close as radius r of the centre, on a circular or a radial orbit.
• The central densities can be entered in various units. Click on a field to make it the currently valid input field (marked in light green).
• The radial distributions of dark matter and ICM follow beta profiles with the parameters specified by the user.
• The hot ICM is observed in the X-rays, and its distribution is often described by a beta profile. From this and the observed (or assumed) temperature on then deduces the distribution of the dark matter by assuming hydrostatic equilibrium:
• To compute this, select masses vs. log. radius. Clicking the wipe&plot button will show three curves:
1. blue: the ICM distribution
2. red: the deduced dark matter distribution
3. black: the dark matter distribution with its current beta profile parameters
Now change the parameters for the dark matter beta-profile until the black curve matches the red curve in the range of radii for which you seek a good representation of the deduced dark matter with a beta profile.
• Selecting e.g. pressures you then get the range of maximum ram pressures that a galaxy will encounter at different radii on circular and radial orbits.