HEAD 2000, November 2000
Session 18. Cluster Surveys/Galaxies
Oral, Tuesday, November 7, 2000, 1:00-2:30pm, Pago Pago Ballroom

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[18.03] MACS: The Most Massive Galaxy Clusters at z > 0.3

H. Ebeling (Institute for Astronomy), A.C. Edge (University of Durham), J.P. Henry (Institute for Astronomy)

The MAssive Cluster Survey (MACS) has begun to compile the largest sample ever of massive, distant (z>0.3) clusters of galaxies with the aim of taking cluster evolution studies from the qualitative to the quantitative level. Based on ROSAT All-Sky Survey (RASS) data and covering a solid angle more than 22,000 deg2 our X-ray flux limited and strictly X-ray selected survey systematically identifies all spectrally hard RASS sources in search of distant cluster candidates.

To date, MACS has discovered 88 clusters at 0.3< z< 0.6. By design all of them feature X-ray luminosities in excess of 5\times 1044 h-250 erg s-1 (0.1-2.4 keV); 60 have LX>1\times 1045 h-250 erg s-1. MACS thus finds the systems that are sparsely sampled by serendipitous X-ray cluster surveys, namely the high-redshift counterparts of the most massive, best-studied clusters at z<0.3. Already at this point (Aug 2000), at an estimated completeness of the full sample of ~60%, the MACS sample is more than 10 times larger than the EMSS cluster sample in the same redshift and luminosity range; at LX>1\times 1045 h-250 erg s-1 the current MACS sample is also larger than the sample of similarly X-ray luminous clusters known in the local universe (z<0.3).

MACS is the first X-ray cluster survey to provide a large, statistically well-defined sample of distant, massive clusters to allow detailed studies and accurate measurements of the properties of the subset of the cluster population that is most sensitive to the cosmological and physical parameters of structure formation and evolution. We here describe the design of the MACS survey, report on the status of the survey including ongoing and planned follow-up observations at radio, sub-mm, optical, and X-ray wavelengths, and present first quantitative conclusions concerning the evolution of massive clusters of galaxies at z>0.3.

MACS is funded by a 5-year NASA LTSA grant.

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