XXL Map of Galaxy Clusters

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.

XXL

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!

 

5 Responses to “XXL Map of Galaxy Clusters”

  1. Despite what the ESA press release says, the XXL survey nothing like the largest ever survey of galaxy clusters undertaken. It is, however, the largest single observing program performed by XMM-Newton, so maybe the superlative generator got its wires crossed in the press release machine!

    Of course that doesn’t mean that we won’t be doing lots of interesting science with the XXL clusters – the first batch of papers are on the arxiv. The survey is remarkable compared to other X-ray clusters surveys for its combination of depth, contiguous area, and spatial resolution.

    Disclosure – I’m a member of the XXL consortium.

    • telescoper Says:

      Thanks. A number of people have pointed our that error. The claim did sound a bit odd, but I didn’t bother to check accuracy of the Press Release…

  2. How do they make a detection in the black region, near center, where they have no data?

    • telescoper Says:

      That’s there as a test to see who is paying attention.

    • Actually, there are data in the central black area. However, the background noise was too high to include them in this good looking map. This did not prevent the detection of a cluster though.

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