Difference between revisions of "SLAC-2017:Clusters"

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High level:
High level:
* Define neutrino mass requirement from cluster counts
* Define neutrino mass requirement from cluster counts
* Define DE/growth function requirement from kSZ
* Define sigma(w(z)) requirement from counts, and growth function requirement from kSZ
* Define reionization requirement
* Define reionization requirement
* Define astrophysics requirements (e.g. on feedback parameters)
* Define astrophysics requirements (e.g. on feedback parameters)

Revision as of 21:03, 27 February 2017

Back to SLAC-2017 main page

Clusters and High ell science

Chairing: David Spergel

General context

Cosmology focused part - mnu and w

  • 11.08 - 11.18 Nick Battaglia - mnu and w from lensing-calibrated clusters slides
  • 11.20 - 11.30 Mat Madhavacheril - mnu and w from CMB-calibrated clusters slides
  • 11.32 - 11.42 Colin Hill - mnu and w from tSZ power spectrum slides
  • 11.44 - 11.49 Lindsey Bleem - Cluster Simulation tools at ANL here
  • 11.50 - 12.00 Christian Reichardt - forecasting cosmology from cluster lensing, and kSZ with 4MOST File:20170227 cmbs4.pdf
  • 12.02 - 12.12 David Alonso - growth function from kSZ, comparison to DESI/Euclid File:KSZgrowth.pdf

Astrophysics focused part - reionization and cluster astrophysics

  • 12.14 - 12.24 Simone Ferraro - reionization case from kSZ slides
  • 12.26 - 12.36 Nick Battaglia - cluster astro case from tSZ+kSZ slides
  • 12.38 - 12.48 Jim Bartlett - Probing the Circumgalactic Medium File:Bartlett.pdf
  • David Spergel - few minute wrap-up

Notes from session

Notes from Steve Allen's talk:

  • 1 arcminute resolution provides an enormous increase in cluster discovery potential relative to 3 arcminutes
  • 1 arcminute would greatly increase galaxy science, and the size of the community served.

Here is the strawman conversion between size of telescope and FWHM as a function of channel that Mat and Nick were looking at (provided by Darcy Barron/Mike Niemack). Just a strawman. Ignore the noise column.

Tel size.png


  • Can do extraordinary things in cluster astro and cluster cosmology with sufficiently small beam.
  • Current leading catalogs are X-ray, optical, SZ. Need a well-defined selection function, and mass-observable relation. This used to be a problem. But, now we split into two parts: relative mass (x-rays) and absolute mass (lensing).
  • Current best constraints are Mantz et al from 220 ROSAT clusters, z<0.5, with Chandra follow-up and WtG WL masses. Similar results come from from Planck clusters. Currently have 15% on DE w from clusters.
  • Radical change coming. Optical: DES/HSC, Euclid, LSST. Mm: SPT-3G, ACT, S4. End of 2017 eROSITA for X-ray.
  • Strengths for optical: cluster finding, photo-z, WL mass calibration. Strengths for mm: high-z clusters, CMB-WL mass calibration. Strengths for X-rays: cluster-finding, low-scatter mass proxies.
  • Target: 100k clusters; far stronger in combination.
  • Optical clusters are limited to z=1.2. X-ray eROSITA find all clusters at low-z, some up to 1.5. Unique discovery space for CMB is at z=1.5 and above, up to z=3. A beam of 3’ loses much of the science.
  • On galaxy cluster astrophysics: we can find virialized haloes out to where they first formed. Things to study: Impact of environment on triggering and quenching of star formation and AGN activity. Evolution of feedback process. Integrated history of star formation.
  • The majority of SPT papers came from cluster astrophysics/cosmology and galaxy astrophysics. (Spergel - ACT too)
  • Conclusion: with 1’ we can be transformative.
  • Douglas Scott: dubious about cluster cosmology. Allen: results have held up.


  • Forecasting constraining power of mass-calibrated SZ cluster counts
  • Summary of code: non-white-noise, 1.5 uK’ at 90 and 150, includes extragalactic foregrounds, marginalizes over scaling relation. Planck tau prior 0.01.
  • Need to calibrate SZ masses, here use optical WL to get mass errors as function of mass. Assume HSC-like coverage and use optical WL out to z=1 or z=2.
  • Going from 5m to 6m to 7m does not affect counts and forecasts, but 3m is much worse
  • Main conclusion: neutrino mass is well constrained by clusters +Planck (as good as CMB lensing +DESI), using both z=1 and z=2
  • Completely independent and complementary to lensing and DESI. Forecast a better w than DESI BAO.
  • Going from 5m to 7m gets about 2x more clusters.
  • Optical surveys are required to obtain redshifts.
  • Requirements: couple percent on w, and 2.5-3 sigma on mnu minimal mass.
  • Allen: likely can do even better, and may want higher res, if look at w model that varies at high z.

(Jo is also taking notes, will paste after session!)

Action items/Next steps

Summarize action items here

High level:

  • Define neutrino mass requirement from cluster counts
  • Define sigma(w(z)) requirement from counts, and growth function requirement from kSZ
  • Define reionization requirement
  • Define astrophysics requirements (e.g. on feedback parameters)
  • Then define measurement requirements for these things

Details that came up in talks include:

  • Extend cluster forecasts to extended w models, check resolution requirements
  • Look at 4m-5m range
  • Include scatter in scaling relation
  • Combine cluster counts and SZ pdf together
  • Compare patchy reionization constraints clearly to 21cm