We examine the cosmological constraints that can be achieved with a galaxy cluster survey with the future CORE space mission .
Using realistic simulations of the millimeter sky , produced with the latest version of the Planck Sky Model , we characterize the CORE cluster catalogues as a function of the main mission performance parameters .
We pay particular attention to telescope size , key to improved angular resolution , and discuss the comparison and the complementarity of CORE with ambitious future ground-based CMB experiments that could be deployed in the next decade . A possible CORE mission concept with a 150 cm diameter primary mirror can detect of the order of 50,000 clusters through the thermal Sunyaev-Zeldovich effect ( SZE ) .
The total yield increases ( decreases ) by 25 % when increasing ( decreasing ) the mirror diameter by 30 cm .
The 150 cm telescope configuration will detect the most massive clusters ( > 10 ^ { 14 } M _ { \odot } ) at redshift z > 1.5 over the whole sky , although the exact number above this redshift is tied to the uncertain evolution of the cluster SZE flux-mass relation ; assuming self-similar evolution , CORE will detect \sim 500 clusters at redshift z > 1.5 .
This changes to 800 ( 200 ) when increasing ( decreasing ) the mirror size by 30 cm . CORE will be able to measure individual cluster halo masses through lensing of the cosmic microwave background anisotropies with a 1- \sigma sensitivity of 4 \times 10 ^ { 14 } M _ { \odot } , for a 120 cm aperture telescope , and 10 ^ { 14 } M _ { \odot } for a 180 cm one . From the ground , we estimate that , for example , a survey with about 150,000 detectors at the focus of 350 cm telescopes observing 65 % of the sky from Atacama would be shallower than CORE and detect about 11,000 clusters , while a survey from the South Pole with the same number of detectors observing 25 % of sky with a 10 m telescope is expected to be deeper and to detect about 70,000 clusters .
When combined with such a South Pole survey , CORE would reach a limiting mass of M _ { 500 } \sim 2 - 3 \times 10 ^ { 13 } M _ { \odot } and detect 220,000 clusters ( 5 sigma detection limit ) . Cosmological constraints from CORE cluster counts alone are competitive with other scheduled large scale structure surveys in the 2020 ’ s for measuring the dark energy equation-of-state parameters w _ { 0 } and w _ { a } ( \sigma _ { w _ { 0 } } = 0.28 , \sigma _ { w _ { a } } = 0.31 ) .
In combination with primary CMB constraints , CORE cluster counts can further reduce these error bars on w _ { 0 } and w _ { a } to 0.05 and 0.13 respectively , and constrain the sum of the neutrino masses , \Sigma m _ { \nu } , to 39 { meV } ( 1 sigma ) . The wide frequency coverage of CORE , 60 - 600 GHz , will enable measurement of the relativistic thermal SZE by stacking clusters .
Contamination by dust emission from the clusters , however , makes constraining the temperature of the intracluster medium difficult .
The kinetic SZE pairwise momentum will be extracted with S / N = 70 in the foreground-cleaned CMB map .
Measurements of T _ { CMB } ( z ) using CORE clusters will establish competitive constraints on the evolution of the CMB temperature : ( 1 + z ) ^ { 1 - \beta } , with an uncertainty of \sigma _ { \beta } \lesssim 2.7 \times 10 ^ { -3 } at low redshift ( z \lesssim 1 ) .
The wide frequency coverage also enables clean extraction of a map of the diffuse SZE signal over the sky , substantially reducing contamination by foregrounds compared to the Planck SZE map extraction .
Our analysis of the one-dimensional distribution of Compton- y values in the simulated map finds an order of magnitude improvement in constraints on \sigma _ { 8 } over the Planck result , demonstrating the potential of this cosmological probe with CORE .