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

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Key Questions

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?
  • Characterize other systematics: CIB, gastrophysics, kSZ from clusters, ...


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? What are systematics from TT based estimates (e.g., from tSZ leakage, cluster kSZ, etc.)?

Cmb lens mass calibration hu et al 2006.png

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

Tsz ps.pngTsz skewness.png

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

HkSZ from Calabrese 2014.png


  • Diffuse tSZ x optical weak lensing

Tsz x cfht.pngTsz x cmb lensing.png

  • Diffuse tSZ x CMB lensing forecast Planck + S3 CMB + LSST & Euclid (see Battaglia, Hill * Murray for tSZ x CMB & optical weak-lensing measurements


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


  • Mass calibration required and possible from optical Stage-4. (Left) Mass calibration required to be limited by Poisson statistics at various mass thresholds for a 10,000 deg^2 survey ( (Right) Mass accuracy from an optical stacked WL Stage-4 experiment.

Dm vs z.pngDm vs z stacked wl.png

  • Dark Energy FOM and growth constraints from a SZ cluster survey. (Left, Right) Improvement in DE FOM and growth from a S4 cluster survey, taken from (, contours represent improvement from a cluster survey with a 8, 4, 2, 1e14 Msun mass threshold.

De fom clusters.png

  • Constraints on neutrino mass. (Left) Euclid cluster survey constraints on sigma8, neutrino mass, which project a ~ 0.01 eV constraint on the sum of the neutrino masses from clusters alone (

Euclid clusters neutrinos.png


  • Simulations that incorporate lensing and gastrophysics will be key to understanding the cosmology constraints; what do we need here?
  • Cluster and galaxy gastro-physics (e.g., shape of tSZ spectrum, galaxy cross-correlations, follow-up of highest redshift clusters)

See Battaglia et al 2010 ( & McCarthy et al 2014 ( for gastrophysical impacts on the tSZ PS


See Battaglia, Hill & Murray 2015 ( for gastrophysical impacts on the tSZ x lensing cross spectrum)


  • Projected emissive point source catalog
  • Cosmic infrared background