NOAO >   Observing Info >   Approved Programs >   2005A-0174

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Proposal Information for 2005A-0174


PI: Megan Donahue, Michigan State University, donahue@pa.msu.edu
Address: Physics Department, 3275 Biomed and Physical Science, East Lansing, MI 48824-2320, USA

CoI: Mark Dickinson, National Optical Astronomy Observatories
CoI: Piero Rosati, European Southern Observatory
CoI: Marc Postman, Space Telescope Science Institute
CoI: Mark Voit, Michigan State University

Title: Harvesting the High Redshift Cluster Candidates from the ROX Survey

Abstract: Positively identified galaxy clusters at z>1 are still rare and prized objects, desirable for cosmological and galaxy evolution studies. Our primary goal here is to identify extended X-ray sources from the ROSAT Optical X-ray Survey (ROXS, 2002) that are likely to be galaxy clusters at z>1. The presence of extended X-ray emission is an extremely robust indicator of a massive gravitational potential and an unambiguous signature of a galaxy cluster. Of the 52 extended X-ray sources in ROXS, 12 did not have a significant cluster counterpart in our I-band data (I<21-22), which should have been sufficient to detect clusters nearer than z ~ 1. We propose to obtain deep (m<20) J and K-band imaging of these 12 high-redshift cluster candidates. The color information is necessary to confirm each cluster's red sequence and to aid in redshift estimation. Ground-based near-IR followup of other X-ray surveys has shown that massive clusters are detectable to z~1.3. With these observations we expect to harvest at least 6 new high-redshift clusters from the ROX Survey while critically cross- testing optical and X-ray methods for cluster identification.


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NOAO >   Observing Info >   Approved Programs >   2005A-0174

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