UMICH-2015: Dark Energy / Gravity / Dark Matter break-out session 2

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Key Science Questions:

  • What are the cosmological constraints on dark energy, modified gravity, and neutrinos from a CMB-S4 SZ cluster survey?
  • What new cosmological probes will be enabled by overlap other multi-wavelength surveys?

Key Instrumental and Systematics Questions:

  • How many clusters (vs mass and redshift) will CMB-S4 detect? How will this vary with beam size, frequency coverage, and depth? Are foregrounds an issue (e.g. sources in clusters)?
  • How well can we calibrate cluster masses? What are the most promising techniques / measurements for reducing uncertainty, and improving cosmological constraints?

SZ Cluster Survey:

  • Plot of N(M,z) cluster counts for different S4 configurations. (S4 assumed depth of 1 uK-arcmin at 150 GHz, 2 uK-arcmin at 90, 220 GHz). (Left) N(z) per 4000 deg^2 survey. S4 would find roughly 19,000, 9,500, or 6,200 clusters for a 1,2,3 arcmin angular resolution survey, respectively, at a S/N ~ 4.5 (approximately a 99% purity threshold). For comparison, SPT-3G would find about 13,500 clusters over the same area at the stated SPT-3G survey depth (2.5 uK-arcmin at 150 GHz). (Right) the 50% completeness level of the S4 cluster survey

Dndz 19sep15.pngMass vs z cmbs4 20sep15.png

  • CMB cluster lensing. S/N of detection for different CMB S4 configurations. Translate to mass calibration vs mass and redshift. For ~100,000 clusters we would expect a ~0.5% mass calibration at a 1 uK-arcmin depth (Hu et al. 2006). How does this vary with beam size? How does this translate to cosmology?

Cmb lens mass calibration hu et al 2006.png

  • tSZ power spectrum projection: 1-d pdf, auto-spectrum, bispectrum

Estimate of cosmic variance-limited experiment's SNR on the tSZ auto-spectrum (from ) -- presumably not far off from S4, though very dependent on number of frequency channels / component separation details, which are TBD

TSZ power spectrum forecast.png

  • kSZ power spectrum: constraints on sigma8


  • Diffuse tSZ x optical weak lensing
  • Diffuse tSZ x CMB lensing
  • Joint SZ+Optical cluster survey
  • Cluster mass constraints / calibration from optical weak lensing (e.g., overlap with LSST, Euclid, WFIRST)


  • Dark Energy FOM from SZ cluster survey.
  • Constraints on neutrino mass, sigma8


  • Cluster and galaxy gastro-physics (e.g., shape of tSZ spectrum, galaxy cross-correlations, follow-up of highest redshift clusters)
  • Projected emissive point source catalog
  • Cosmic infrared background