NXS Observing at KPNO March/April 2009 [4m 05B-0045 run Mar 25-Apr 1, 2009]

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To measure photometric redshifts for about 50 X-ray cluster candidates from the XCS cluster survey. This is the final allocation of time (8 nights) for the NXS project (40 nights total) on NOAO 4m telescopes (CTIO and KPNO). XCS is a international collaboration led by Dr Kathy Romer at the University of Sussex. XCS aims to find all the X-ray clusters detected by accident by the XMM satellite during its 10 year lifespan, and then to use them to attack a variety of science questions in extra galactic astronomy and cosmology. The NXS data are being processed by an STFC supported PhD student at the University of Sussex, Nicola Mehrtens. She has found that redshifts can be measured in a robust way using images, rather than the more traditional - and time consuming - spectroscopy method. Through the combination of the NXS imaging with X-ray data available from the XMM, we are able to make a variety of scientific conclusions. These conclusions range from the way galaxies evolve in massive clusters to measurements of fundamental cosmological parameters (including the energy density of dark energy). The NXS project has been a major international endeavor, spanning 3 years and 8 telescope campaigns. The final campaign was awarded to NXS by NOAO to compensate for instrument problems during a previous run. It gives us a unique opportunity to complete the redshift coverage for our cluster sample in a particularly rich region of the sky (the North Galactic cap is visible during this run).