galaxy clusters as cosmic probes

Galaxy Clusters as

Cosmic Probes

Subha Majumdar

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Cluster Cosmology - A flavour of decades old results

Pre WMAP - 1999 Science article Bahcall, Ostriker, Steinhardt

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In this era of CMB, SNe, etc Why do we need clusters?

LSST forecast: Strengths of different approaches within one single survey

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Cluster surveys / observational programs (incomplete list) Red Sequence Cluster Survey (RCS) Spitzer Adaptation of the RCS (SpARCS) Spitzer Legacy Extremeley Wide Survey (SLEWS) Gemini Cluster Astrophysics Spectroscopic Survey (GCLASS) South Pole Telescope (SPT) APEX-SZ Atacama Cosmology Telescope (ACT) Blanco Cosmology Survey Sunyaev-Zeldovich Array (SZA) ROSAT XMM-LSS Serendipitous Survey XMM-Cluster Survey Pan-Starrs Dark Energy Survey (DES) Hyper SuprimeCam (HSC) Large Synoptic Survey Telescope (LSST) eROSITA, Wide Field Xray Telescope AMIBA, SuZIE, Cluster Imaging Experiment, Cluster Cosmology Atacama Telescope

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South Pole Telescope papers are rolling in…

6+1 papersince June2009

Results arefull ofsurprises!!

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Atacama Cosmology Telescope papers are not behind…

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What are clusters?How do they form?

What do they contain?AND

How are they distributed?

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The WMAP SkyThe WMAP Sky

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QuickTime™ and a decompressor

are needed to see this picture.

Counting clusters: mass function, growth fn & 8:

Universality when written in terms M

Seth-Tormen: ellipsoidal collapse & Nbody

Jenkins etal, bestfit to simulationsAlso Warren etal, Lukic etal latest.

[8 for R=8h-1 Mpc]

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Cosmology with Cluster Number Counts

(with apologies to)1. with Xray luminosity function

2. Xray temperature function3. Xray gas mass fraction

4. Optical/Xray cluster 3D corr fn5. Optical/Xray 2D angular correlations

6. SZ+XR method of Hubble Const

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Cosmology affects cluster counts -

Almost 10 years back…Weller, Battye & Kneissi 2002

Ncl = 5200 Ncl = 1972 Ncl =90

Ncl = 13600

Fixed Mlim --> so NO uncertainty in cluster physics --> unrealistic , good as first attempt.

SNAP

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Chandra Image of Zw38

Problem is we have to deal with real clusters!

Large peak in matter density– Dark matter clump (~80% of

mass)– Many luminous galaxies (~2%:

10% of baryons)• BCG and red sequence• Additional galaxies• Diffuse light

– Hot gas (~18%: 90% of baryons)• Emits X-rays • Causes SZ decrement in

microwave background

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Cluster Physics Interplay -

€

fx z( )4πdL2 = AM β E 2 z( ) 1+ z( )

γExample SZ scaling:

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Example - Lets talk about scatter…

Scatter can boost signal, ex: Cl’s or n(z)Reason : shape of the mass function. Widens the range of possible masses for fixed value of the observableInclude it by convolving the mass fn with distribution of the scatter

Distribution of observable Probability of assigning obs mass-true mass

mass fn scaling

Standard assumption: gaussian scatter in loglog plane

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Scatter and cosmology :Scatter – 8 degeneracy in dn/dz

Pdf of 8 with priors on scatter

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1. Using the cluster power spectrum and P(k) oscillations2. Adding information from counts-in-cell3. Shape of mass-function in redshift slices (Majumdar & Mohr, Lima & Hu)

Self-Calibration - A paradigm shift in cluster cosmology

Use complimentary information from the survey itselfe.g. the mass dependence of bias / spatial distribution

Unbiased parameter estimation with small error bars in the presenceof systematics.

This idea has now propagated to other fields in cosmology - Weak Lensing Galaxy Bias BAO Photo-z Non-gaussianity from LSS etc

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Self Calibration using Cluster Power Spectrum

Power spectrum of dark matter density fluctuations P(k)– Clusters are biased: 20,000 clusters comparable to ~5x105 galaxies– Turnover on large scales- “standard rod” calibrated by primary CMB fluctuations

DUET P(k)

From redshift surveys, we will get P(k) for free !

Unfortunately, only P(k)gives almost no constraintson `w’. Combined with CMBpriors, one can constraintw ~ 25-30%Things become interestingwhen dn/dz and P(k) are Combined.

SM & J.Mohr 2003

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Prospects for Self-Calibrating Cluster Survey…

SM & J Mohr, 2003

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Some ideas on what to expect on DE …

Xray - < 5-10% for eROSITA ~ 1% like from WFXTSimilar constraints from optical with similar cluster numbersIgnore SZE for now!

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`The Proof of the Pudding is in Eating’or

Real Results from Real Survey(RCS1 and RCS2)

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• Pre 2009 - • SPT/ACT surveys forecasted to yield 4-7clusters/deg• (Planck ~ 1000 to few 1000)

• Post 2009 - • SPT/ACT finds 0.05-0.12 clusters/degsq• Also finds less SZ power in SZ Cl’s

Implication - Cosmological constraints are washed out !So, will doing cosmology with clusters become secondary science for these SZ surveys ?

Need to do something More with these surveys!

We are in a little spot with recent SZE results…

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Our Options -1. Come up with new ideas for cluster surveys

2a) Make progress with understanding of cluster physics (for cases wherecluster modeling cannot be avoided)2b) Make atleast a useful ‘working’ model of cluster

3) Fall back on some old ideas of combining diff SZE outputs

Example -ACT - 2000 deg2 survey

with tobs~107 s

1800 deg2

200deg2

tL = (1-ftime)tobs

tS = ftimetobs

ftime = fractional time spent on the smaller patch.

2000 deg2

tobs

Quick Thinking 1 - Change Survey Design

A, α, γ unkown γ unkown with follow-up

Ωm 0.676 0.019 0.032

w 1.343 0.400 0.147

σ8 2.849 0.121 0.028

Ωm 0.105 0.009 0.030

w 0.115 0.095 0.088

σ8 0.116 0.019 0.028

Wedding Cake survey(200+1800) deg2.

Single area survey(2000) deg2. factor of 4

improvement!

better than mass follow-

upBIG

improvement!

Bottomline - A simple change of survey plan can do wonders

Magic of a ‘tiered’ survey (in numbers) …(from Satej’s talk)

Overlapping areas for SZE+Xray surveys-An ensemble of dual detected clusters for free

mock catalog of 430 clusters created from

ACT/SPT+eROSITA for Nbeam=2 with minimum 20% errors in

dA(z).

SZ clusters

XRay clusters

Common

Temp

Sizes

ACT/SPT dN/dz only

ACT/SPTdN/dz + dA(430)

100 mass follow-up: 30-100 % error

ACT/SPT dN/dz + SNe(307)

dA from clusters ‘CAN BE LIKE’ dL from Sne !!

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Diego & SM

Use flux counts with SZ Cl to remove cluster uncertainties …

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Higher - z and Larger Surveys -

1. Completed Optical2. Proposed (and failed) Optical3. Upcoming and funded Xray

4. Proposed XRay

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PI - G Wilson (USA)

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…more

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What about masses? - For the cluster in SpARCS SOUTH

Vdisp = 1050 +/- 230 km/sM = 9.4 +/- 6.2 x 1014 Msun 5.7 x 1014 Msun (from scaling)z = 1.34

This cluster just should not exist !!Or maybe a sign of non-gaussianity We are working on it now.

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A comparison of survey volumes …

SDSS: 10000 deg, z<0.5, Vol ~ 7 Gpc3SPT/ACT : 2000- 4000deg, z=0.1 -1, Vol ~ 7-14 Gpc3RCS2: 900 deg, z=0.2-0.9, Vol ~ 2.4 Gpc3 & SpARCS ~ 0.5 Gpc3

350 deg, z=1-2 Vol ~ 3.6 Gpc3 high-z survey having smaller area has same leverage due to Its higher volume!

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Becoming more ambitious - More with Spitzer

Proposed, for ~3000 hours (i. e., 4 months of Spitzer time) making it a legacyclass survey:

The Spitzer Legacy Extremely Wide Survey (SLEWS)PI: Jonathan Gardner (NASA) & Gillian Wilson (UCRiverside)(Multi country, multi supportive PI from other surveys, huge teamTotal members : 84 (with different backgrounds and expertise) Roughly 59 (USA), 24 (Europe + Japan), 1 (India)

Basic coverage: 350 deg2 , 1< z < 2Basic aim: a) To do clusters at high z b) To do quasars at z>6.5 when reionization is about to occur and there are probable stromgen spheres

Passed initial stages but finally lost to a ExoPlanet Survey :-(

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Into the ‘not too distant future’ - Wide Field Xray Telescope(Mission pushed ahead by R. Giacconi , 2010 Decadal Survey)

If funded, this will be the mother of all cluster surveys

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Forecast for WFXT - using N(z) + P(k)

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Cluster constraints on ‘generalised’ modified gravity models

with

= 0.55 for standard model (GR+CDM)

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Can India have a world class optical survey ???A comparison -

Telescope RCS on 4m CFHT 2m in Hanle

Seeing 0.7 arc sec <1 arc sec

Resolution 0.187 arc sec 0.45 arc sec

FOV 1 deg sq 0.7 arc-min sq30 arc-min sq

RCS1 (100 degsq) - Equivalent time

~ 27 - 40 hrs ~ 1350-2000 hrsor 54 - 80 hrs

I think its possible with a little effort !!Technology additions are easy and cheap.

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Thanks

Thanks also to Ravi Subrahmanyan, Biman Nath, Joe MohrMartin White, Dick Bond, Wayne Hu, Nabila Aghanim, Joe Silk, Christoph Pfrommer, Nick Battaglia, Jon Sievers,Sudeep Das, Jose Diego,Bhuvnesh Jain, Howard Yee, Mike Gladders, Henk Hoekstra, Gillian Wilson, Adam Muzzin, Yen Ting Lin , Alexey Vikhlinin, Salman Habib, David GilbankZoltan Haiman + Satej Khedekar & Anya Chaudhuri.