Learning Center
Plans & pricing Sign in
Sign Out

Future Prospects for Sunyaev-Zeldovich Effect Studies


       Cluster Surveys

                    Subha Majumdar

   Canadian Institute of Theoretical Astrophysics

           along with Joe Mohr, Martin White & Jose Diego

International Conference on Gravitation and Cosmology, Kochi, 5th January 2004
              Introduction to Galaxy Clusters
              Introduction to the Surveys
              Studying Dark Energy with Galaxy Cluster Surveys,
               the stress in on the eqn. of state “w” of dark energy

                 (This was the parameter that was not constrained by WMAP+SDSS!
                 But knowledge of “w” is fundamental to our understanding of dark

              Something new: Self Calibration in cluster surveys
               and precision cosmology

Jan 2004                                ICGC – 04, Kochi
What Are Galaxy Clusters?
Galaxy clusters are the most                        HST
                                                      Chandra Image of Zw3158
   massive, collapsed structures in
   the universe. They contain
   galaxies, hot, ionized gas (107-8K)
   and dark matter.

In typical structure formation
    scenarios, low mass clusters
    emerge in significant numbers at
Clusters are good probes, because                     X-ray

    they are massive and “easy” to
    detect through their:
  • X-ray emission
 • Sunyaev-Zel’dovich Effect
 • Gravitational lensing

Jan 2004                         ICGC – 04, Kochi
The Basics of SZ Effect

   distortion  freq _ dependence amplitude(cluster)
   amplitude            gas _ pressure
                 line  of  sight

Jan 2004                              ICGC – 04, Kochi
Whats nice about SZE?
      1) Ofcourse, the distinct spectral signature
      2) Measures the total thermal content of the cluster
      3) More or less redshift independent
      4) Less susceptible to messy cluster substructure, core
         physics (prop to density and not density squared as in XRays)

Jan 2004                    ICGC – 04, Kochi
   Example: Local Abundance/Mass Function
                             Reiprich & Boehringer 2001

 Look at the large error bars!! We want to do much better.

            Things will change drastically with future surveys.
           Especially as a probe of dark energy eqn `of state “w”

Jan 2004                           ICGC – 04, Kochi
  Upcoming Cluster Surveys
  Planck    :    2008(?)       7,000/8,000 – 30,000/40,000
  SPT       :    2005(?)       20,000-30,000
  ACT        :   late 2004     few thousands
  APEX      :    middle 2004   few thousands

X-Ray surveys

DUET   : Unsuccesful                        20,000-30,000
DUO    : very +ve report, late 2004         ~10,000
XMM-LSS : 2004+ ,                           ~1000(?)

      Cluster surveys will be a thrust area for some time to come!
Jan 2004                    ICGC – 04, Kochi
From observations to detecting clusters:
                           an example

Diego & SM 04

Jan 2004         ICGC – 04, Kochi
    The Cluster Redshift Distribution

           One can get dN/dz if we can get the redshifts of the detected clusters

     Cluster redshift distribution probes:
             1) volume-redshift relation
             2) abundance evolution
             3) cluster structure and evolution.          Mass Selection Function

           dN(z) dV
                     nz   c d 2 1 z2  dM f M  dn M , z
           dzd dz d        H z A
                                            0             dM
                 Volume    Abundance         Volume                  Abundance

Jan 2004                               ICGC – 04, Kochi
   Sensitivity of Cluster Redshift Distribution to
   Dark Energy Equation of State

Increasing w keeping E fixed
 hasthe following effects

             It decreases
           volume surveyed

      It decreases growth
     rate of perturbations

                                    Volume effect                   Growth Effect
Jan 2004                     ICGC – 04, Kochi       Fig courtesy Joe Mohr
Potential for different methods to
constrain `w’

                                                   Highly Competetive

  Levine, Shultz & White 2002

Jan 2004                        ICGC – 04, Kochi
Dual Nature of Galaxy Clusters
      It’s critical- for almost any analysis- to keep in mind that clusters
       are young objects and yet as a population they exhibit striking

      Statistical studies of (x-ray flux limited samples of) galaxy
       clusters reveal that more than half exhibit merger signatures.
       There’s lot of substructures.

      Statistical studies of (x-ray flux limited samples of) galaxy
       clusters reveal regularity

                   Existence of simple flux-mass relation

Jan 2004                         ICGC – 04, Kochi
       Self-Calibration in SZ surveys
     Two surveys, the South Pole Telescope                   Assumptions required:
      Survey and the Planck all sky survey                       1.    Hierarchichal structure formation is
      (yielding > 20000 clusters), contain                             correct
      enough information to constrain the                        2.    A mass-X-ray luminosity relation
      interesting cosmological parameters and                          exists (or a mass-SZE luminosity
      solve for the structure of galaxy clusters                       relation exists)
      simultaneously!                                            3.    Crude redshift estimates are
                                                                       available for each cluster detected in
                                                                       the survey

                                   f x z4dL  AM  E 2 z

        Survey       m      tot       w         s8       h            n        b       Norm    Slope
        Priors              flat                        0.07          0.050    0.004
        Planck      0.017    -        0.075    0.013    0.053         0.041    0.004     24%      0.004
                  0.024    -        0.062    0.013    0.047         0.048    0.004     21%      0.005
                                                                                       SM & J. Mohr 2003

    Jan 2004                                  ICGC – 04, Kochi
Self-Calibration : Continued

A Caveat:       What if there is “evolution” ??
                    f x z4 d  AM E z1 z
                                                 2

                                     Everything is lost ! Or is it?

 Self Calibration can be regained (by adding complimentary info) !
          1. Need to do follow-up mass estimates of a few clusters
          2. Cluster power spectrum, P(k)

       Not impressive by themselves, when combined with dN/dz they do wonders

Jan 2004                            ICGC – 04, Kochi
An Example: Planck All Sky Cluster Survey
                Nclusters ~ 22000

                                    SM & J. Mohr, 2004

Jan 2004         ICGC – 04, Kochi
How well do we get `w’ ?
           1s error around w=-1, normalized over 9 other parameters

Survey         On its          + P(k)              +100       + Both
               own                                 clusters
SPT            0.18            0.16                0.06       0.035
Planck         0.39            0.10                0.12          0.041

                       Note: WMAPext gives ~ 0.11
 To pin down dark energy we must have cluster surveys + (CMB+SNe)

Jan 2004                        ICGC – 04, Kochi
So what did I say,
  Upcoming large yield cluster surveys would unveil a new
era of doing cosmology with clusters.
    It has the promise to become 4th pillar of precision cosmology
along with CMB, SNe and weak lensing.

   As an example, we have shown that these surveys provide us an
opportunity to probe the enigma of dark energy with high precision
                       (the other great way is to do weak lensing tomography)

 Most importantly, we’ve seen that even with uncertainties in cluster
physics, `self-calibration’ in these surveys makes clusters an important
tool in precision cosmology           ( “w” to few percents, certainly competetive or maybe
even better than what can be done with CMB or SNe alone. )

Jan 2004                                ICGC – 04, Kochi

To top