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The ultimate galaxy cluster survey

The Sunyaev-Zeldovich (SZ) effect is the method of choice for assembling a catalog of clusters at high redshift, of particular interest for cosmology because of the tight correlation between integrated y-distortion and cluster mass. When PRISM flies, all-sky cluster samples (e.g. from eROSITA, EUCLID) will likely count some 105 objects, mostly at z < 1. PRISM will find 10 times more clusters extending to deeper redshifts, with many thousands beyond z = 2. In fact, PRISM will detect all clusters in the universe of mass larger than 1014 solar masses, and a large fraction of those with mass above 5×1013 solar masses. Owing to its exquisite spectral coverage, angular resolution and sensitivity, PRISM will measure the peculiar velocity of hundreds of thousands of clusters via the kinetic SZ effect, initiating a new research area: the complete mapping of the large-scale velocity field throughout the Hubble volume. In addition, PRISM will also be able to probe the relativistic corrections to the classic SZ spectral distortion spectrum, thus measuring the gas temperature. This cluster sample will allow us to probe dark energy and better understand structure formation at large redshift.

fig1a
Lower mass limits for detection of the labeled SZ effects at signal-to-noise S/N > 5 as a function of redshift.

fig1b
The completeness of the detection for all three effects, as a function of mass. Objects more massive than 4 × 1013 solar masses are detected at more than 5σ at all redshifts, a limit extending well down into the relatively unexplored group range (light blue line). PRISM is able to measure peculiar velocities over most of the cluster range, i.e., for M > 2 × 1014 solar masses (dashed yellow line), and relativistic effects, giving access to cluster temperature, for the more massive systems (dot-dashed purple line), both out to high redshift. Note that in practice, the detection depth will be lower close to the galactic plane, where a fraction of the clusters will inevitably be missed (although this should be only a very small fraction of the total).