Archive for December 18, 2015

XXL Map of Galaxy Clusters

Posted in The Universe and Stuff with tags , on December 18, 2015 by telescoper

The press office at the European Space Agency is apparently determined to release as much interesting material as possible in the week before Christmas so that as few people as possible will notice. I mentioned one yesterday, and here is another.


The map is of preliminary data from the XXL Cluster Survey, the largest survey of galaxy clusters ever undertaken, and was obtained using the XMM-Newton telescope. (Thanks to various people, including Ben Maughan below who pointed out the error I made by relying on the accuracy of the ESA Press Release.)

The press-release marks the publication of the first results from this survey on 15th December 2015. The clusters of galaxies surveyed are prominent  features of the large-scale structure of the Universe and to better understand them is to better understand this structure and the circumstances that led to its evolution. So far 450 clusters have been identified – they are indicated by the red rings in the picture. Note that the full moon is shown at the top left to show the size of the sky area surveyed.

If you’ll pardon a touch of autobiography I should point out that my very first publication was on galaxy clusters. It came out in 1986 and was based on data from optically-selected clusters; X-rays emission from the very hot gas they contain is a much better way to identify these than through counting galaxies by their starlight. Cluster cosmology has moved on a lot. So has everything else in cosmology, come to think of it!


Is This the Beginning of the End of the Standard Model?

Posted in The Universe and Stuff on December 18, 2015 by telescoper

Thoughts from a proper particle physicist on the recent announcement from the LHC…

Of Particular Significance

Was yesterday the day when a crack appeared in the Standard Model that will lead to its demise?  Maybe. It was a very interesting day, that’s for sure. [Here’s yesterday’s article on the results as they appeared.]

I find the following plot useful… it shows the results on photon pairs from ATLAS and CMS superposed for comparison.  [I take only the central events from CMS because the events that have a photon in the endcap don’t show much (there are excesses and deficits in the interesting region) and because it makes the plot too cluttered; suffice it to say that the endcap photons show nothing unusual.]  The challenge is that ATLAS uses a linear horizontal axis while CMS uses a logarithmic one, but in the interesting region of 600-800 GeV you can more or less line them up.  Notice that CMS’s bins are narrower than ATLAS’s by a factor…

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