Cosmology seminar: Håkon Dahle
Håkon Dahle is a researcher at ITA.
The power spectrum amplitude from primary CMB anisotropies vs. the Planck SZ cluster counts — problem solved?
One of the highlights of the 2013 Planck results was the apparent discrepancy between the power spectrum amplitude derived from the measurements of the primordial CMB anisotropies and the power spectrum amplitude determined from the abundance of foreground galaxy clusters detected by Planck through the Sunyaev-Zel’dovich effect. This discrepancy could be a signature of a relatively high neutrino mass, new physics, or simply a problem with the mass calibration of the clusters.
A recent work (arXiv:1402.2670) claims that weak gravitational lensing-based mass measurements of a subset of highly X-ray luminous clusters in the Planck SZ cluster catalogue indicate a tension with the cluster mass calibration assumed by the Planck team. I will compare these results with other lensing-based mass measurements of (partially overlapping) samples of clusters. Progress can be made by establishing more complete samples of purely SZ-selected clusters at higher redshifts (z>0.5), where X-ray surveys are less efficient. I will show some results from follow-up programs at NOT and VLT to confirm Planck SZ cluster detections, determine their redshift and velocity dispersions, and measure the masses of the clusters via gravitational lensing. Current results demonstrate that NOT is a very efficient “spectroscopic redshift machine” for new Planck clusters in the range 0.5 < z < 0.7, and that some the “new" Planck clusters in this redshift range include gravitational lenses comparable to the strongest known lenses so far, such as those targeted in the ongoing HST “Frontier fields” programme.