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Session 53 - The X Clusters: Cooling Flows.
Display session, Thursday, January 08
Exhibit Hall,

[53.11] A Complete X-ray Selected Sample of Galaxy Clusters from the ROSAT North Ecliptic Pole Survey

C. R. Mullis, J. P. Henry, I. M. Gioia (IfA, U. Hawaii)

We are using the ROSAT All-Sky Survey observations around the North Ecliptic Pole to construct a complete and unbiased sample of galaxy clusters in order to understand the nature of cluster evolution and determine implications for large scale structure models. Our database is unique in that it is both deep and contiguous.

Here we give an update on the survey's progress and discuss a few particularly exciting results.

Via optical follow-up, we have secured identifications for nearly 80% of the 465 X-ray sources in the survey area. The cluster sample now consists of 50 objects with redshifts approaching unity.

Evidence for large scale structure exists at both low and high redshifts in the NEP survey. A low-z spike in the redshift distribution for NEP clusters is consistent with a previously known supercluster at 0.088.

At the other extreme, we recently discovered a very distant cluster at z=0.813 which resembles a filament of galaxies. Such a massive, un-virialized cluster at high-z may be the vision quest of cosmic-web proponents. For this potential protocluster, we present a velocity dispersion analysis of its member galaxies from Keck II observations and a temperature measurement from ASCA data.

We construct the cluster X-ray luminosity function at high redshifts, incorporating a rigorous treatment of our survey selection function, and compare it to previous work.

Program listing for Thursday