# B Graph of rotation curve of a cluster (not a galaxy)

Tags:
1. Sep 22, 2016

I'm familiar with galactic rotational curves and there are plenty of graphs depicting such curves, but I'm interested in the rotation curves of entire galactic clusters at the moment and I'm not too good with sifting through what shows up in the search engines. (not a physicist, just a hobbyist) Has anyone graphed the rotation curve of any cluster? What I'm interested in learning is:
1) the locations of the galaxies involved relative to the axis of rotation of the cluster (not all, just a handful but at varying distances from the axis)
2) the velocities of these galaxies around the axis of rotation.
3) (optional) The single dimension location of the galaxy along the axis
3) these things depicted in a graph or in the absence of that, the spreadsheet or chart.

I would think this would be out there somewhere, but I'm at a loss how to find it, but perhaps someone here is actually doing work on this sort of thing.

Thanks,

2. Sep 23, 2016

### Chalnoth

One issue is that galaxy clusters don't have a single axis of rotation. Each galaxy in the cluster may be orbiting in a different plane entirely from every other.

Instead, what is measured for galaxy clusters is the velocity dispersion, as you can see here for example:
https://ned.ipac.caltech.edu/level5/Biviano/Biviano6_3.html

3. Sep 25, 2016

Thank you for the reply and insight. Does this mean that clusters are more like elliptical galaxies than spiral galaxies if an analogy were to be drawn? In this case one more thing I would need to know is the plane of rotation and the direction (clockwise or counter clockwise within this plane) for the study I'm trying to do. Is this data just not available in this form?

4. Sep 26, 2016

### Chalnoth

Yes, clusters are more like elliptical galaxies. However, being larger and with fewer constituents* than galaxies, they tend to have less regular shapes.

As for whether the data exists, I don't really know. I suspect that some data on this exists, but it may be difficult to track it down precisely.

* Fewer in the sense that the number of galaxies in a cluster is much, much less than the number of stars in a galaxy.

5. Sep 28, 2016

### ohwilleke

FWIW, clusters have very high proportions of dark matter, while elliptical galaxies have low proportions of dark matter (and the amount of dark matter in an elliptical galaxy is strongly correlated with the extent to which is is not spherical - nearly spherical elliptical galaxies have the least dark matter of any galaxy type).

6. Sep 28, 2016

### Chalnoth

I doubt that has much impact. My understanding is that the prevailing model has the amount of gas and dust in the galaxy being the primary determinant of its fate. Spiral galaxies tend to have a lot more gas and dust, and it is likely that the friction of this material is what causes them to settle into this shape.

From what I recall, the primary way that gas becomes expelled from a galaxy is by radiation pressure from an active galactic nucleus.