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Radio Halos of Galaxies
There were a variety of goals of this workshop, the main scientific ones included probing the origin and physical conditions in galaxy halos and related science such as understanding differences between galaxies, the relation of halos to star formation and to the environment. Thirty-five edge-on galaxies are being imaged in full polarization and at two frequencies. As this was the first face-to-face meeting held by the CHANG-ES consortium, a very important part of the meeting was to ensure good communication between all participants, to present scientific ideas via more formal talks, as well as discuss more informally how the enormous volume of data and data processing could proceed effectively. At the time of the meeting, all data had been acquired, and approximately 25% of the data had been processed. Therefore many details related to data quality were part of the meeting (e.g. how to include single-dish data, how data could be protected for PhD students, how to understand the errors, how to separate thermal from non-thermal emission given our data set, what supplementary data might be needed, etc.). A preliminary outline of scientific papers and who would be the lead author was also drawn up.
Several exciting results were emphasized, some of which were realized and some are in the process of exploration. An example is the discovery of a strong double-lobed radio source immediately behind an edge-on galaxy (UGC 10288), an idea that may open up new possibilities for probing foreground disks and halos (like a flashlight illuminating a foreground source). This result has led to a press release https://public.nrao.edu/news/pressreleases/surprising-image-provides-new-tool which was featured on many websites. The concept is now being followed up more thoroughly as a direct result of the Lorentz Center@Snellius workshop, since it was realized that many such sources around other galaxies may be used as probes of foreground gas and magnetic fields. Moreover, new techniques (such as rotation measure synthesis) permit the more detailed analysis of such systems. Another important result is the prevalence of nuclear cores, at least one of which is varying with time. This science has yet to be fully explored but will be soon. Our discussion of scientific papers has led, among other things, to the organization of our 4th paper and the first that will include all galaxies, namely the results of our low resolution/high sensitivity data, led by Dr. T. Wiegert. This paper is now well-advanced and will also culminate in the first public data release for CHANG-ES.
Our group was very impressed with the support (both organizational and financial) provided by the Lorentz Center and the freedom associated with the workshop format. The size and venue were excellent. Since it was our first meeting, the ratio of formal talks to informal discussions was perhaps higher than might be typical for a Lorentz Center@Snellius workshop, but this was a necessary first step. Having learned from our experience at Lorentz Center@Snellius, our follow-up meeting, to be held in Kingston, Canada, in July 2014, will reverse this emphasis and, in addition, will focus more on new CHANG-ES results. The workshop dinner/cruise was a delight and helped us to become a cohesive group. While some of us knew each other only professionally via scientific publications and occasional conferences, the open communications encouraged by such activity permits scientific ideas to flow as well.
Kudos to the Lorentz Center for being so forward-thinking that such a center exists and is well supported. I would recommend it to others.