Cluster-sized diffuse radio waveband synchrotron radiation
This is the last post in answer to RC's question about what sort of things one should expect to see if one looked at (rich) clusters (of galaxies), in a universe where the model Peratt outlined in his pair of 1986 papers ruled.
Recall that a) we cannot actually answer this question, at least not without running simulations using the same code Peratt used; and b) in any case, Peratt's model is so strongly inconsistent with so many, and so many types of, good astronomical observations that it's safe to say it does not describe the universe we live in. Rather, I have taken a look at clusters with the objective of exploring the extent to which there is any evidence for the ubiquitous galactic-scale filaments so central to that model.
I looked at the visual/optical, x-ray, and radio wavebands. There's no evidence in the first two, because what emission there is is well accounted for by stars (optical) and hot plasma (x-ray), not to mention a lack of filaments*.
For the radio, I introduced
a recent review, by Ferrari et al., pointing out that where diffuse radio emission has been detected from clusters, it bears the signatures of synchrotron radiation ... just what you'd expect from Peratt's filaments.
The first thing to note about this cluster radio emission is that it's pretty rare.
Peratt includes ~50 double-lobed galaxies and quasars in Paper I, and that may seem like a lot; in fact it's the same number (within a factor of two or so) as the
total number of clusters with extended radio emission! To understand just how few this is, consider that the famous
Abell catalogue (of rich, local clusters) has >4,000 members.
So the scarcity of any extended cluster (synchrotron) radio emission would seem to suggest that Peratt's galactic-scale filaments are far from ubiquitous.
Ferrari et al. divide extended cluster radio emission into three classes: radio halos, radio mini-halos, and radio relics, with the last being a heterogenous class comprising "AGN relics", "Phoenix", and "radio gischt". The mini-halos (of which there are only ~10) and AGN relics are closely associated with individual galaxies, and so should be considered wrt Peratt's 1986 papers directly. The radio halos and gischt are clearly associated with cluster collisions/mergers; there are no filaments in the former, and those in the latter seem to arise from shocks that are produced by the collision.
Which leaves just one sub-class of object that might be consistent with Peratt's model, the "Phoenix" radio relics.
So, RC, in a word, no astronomical observations, of rich clusters, that support the Peratt idea, with the possible exception of a particularly rare kind of radio relic found only in a very few merging clusters.
But the extended cluster radio emission, being synchrotron, means there are magnetic fields in galaxy clusters (or at least some clusters), as well as sources of relativistic electrons ... so does this point to a way to rule out the Peratt model more directly?
Yes ... and it also addresses the second of Anaconda's topics (that he wanted to focus discussion on, before he left us); namely, what can we say about the processes - plasma or otherwise or combo - that produce the relativistic electrons that produce the (radio) synchrotron emission, both in clusters and individual galaxies. Stay tuned.
*
one thing I omitted in my earlier posts: Peratt makes it clear that he expects the synchrotron radiation from (galactic-sized) "Bennett-pinched filaments" to be observed from the x-ray to the microwave wavebands ... IOW, the plasma processes will generate copious quantities of (highly) relativistic electrons, and the magnetic fields associated with the field aligned currents are strong enough. Needless to say that a lack of synchrotron emission in wavebands other than the radio (and microwave, depending on how you define the bands) is but one more inconsistency between his model and the observed universe.
