Simulating the SZ Sky

Predictions for Upcoming Sunyaev-Zel’dovich Effect

Galaxy Cluster Surveys

Eric J. Hallman

CASA, University of Colorado

16 February, 2007

Clusters of Galaxies as Cosmological Probes Conference

Aspen, CO

Collaborators

• Brian O’Shea (LANL)

• Jack Burns (University of Colorado)

• Mike Norman (UCSD)

• Rick Wagner (UCSD)

• Robert Harkness (SDSC)

SZ Surveys of Galaxy Clusters

• Survey yield depends on cosmology AND gas physics AND details of dynamical states of clusters

• How does observable scale with mass?

• What is the selection function in mass for cluster surveys?

• Also depends on instrument properties, survey strategy, confusion, etc.

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•ΛCDM m=0.3, =0.7, 8=0.9•AMR gives high resolution (8 h-1 kpc) in dense regions• 512 h-1 Mpc on a side, use 7 levels of refinement• 5123 root grid, 7 levels everywhere•DM mass = 7.3x1010 Msolar, baryon mass = 1.1x1010

•Initial run is adiabatic physics only

Adaptive Mesh Refinement (AMR) Light Cone Simulations (N-body + Hydro)

Enzo (O’Shea et al. 2005, http://cosmos.ucsd.edu/enzo)

How do we make simulated surveys?

• Surveys sample the universe at all observable epochs, so….

• Stack simulations at different evolutionary states in discrete redshift intervals to approximate

• Each z uses physical extent of box in line of sight which matches that redshift interval

• Modify angular scale of image to fixed angular size for all redshifts, flux diminishes (but not in SZE!)

• Random shifting, rotating, some tiling• Model telescope response, background, foreground

contamination, point sources, etc etc (Future work)

Sky Surveys

• X-ray and SZE synthetic surveys• 5000+ Clusters above 1x1014Msolar in field out to z=3• 2048x2048, 10x10 degrees, 17.6” / pixel

Why do we have N-body + hydro?

• In real universe, clusters are neither isothermal nor in equilibrium generally (e.g. M. Voit’s talk)

• Variations in cluster physics make a difference (Evrard’s and Rudd’s talks)

• In order to characterize scatter, survey selection (in mass) from simulations, must include baryons!

Cold Fronts Filaments Bullet Subcluster

1E 0657-56Abell 1795Abell 2256

(Sun et al 2002) (Fabian et al 2001) (Markevitch et al 2002)

Clusters are NOT generally in equilibrium (dynamical, hydrostatic or otherwise)

Merger Boosting

• See also C. Sarazin’s talk

Identification of Sources

• Hallman et al. 2007

Identification with SExtractor

• Upcoming Surveys:

SPT: 1.0’, ~4000deg^2, 10K

APEX-SZ: 1.0’, ?deg^2, 10K

ACT: 1.7’,100-200deg^2,2K

Planck, 5.0’, all-sky, 2.2K

• 90% limits for 200 stacking realizations of the survey

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• APEX: 472 +- 100

• ACT: 1211+- 200

• Planck: 90 +- 40

What else should be included?

• What we get: full array of dynamical stateslarge volumegaussian background

• What we’re missing (so far) ref. N. Sehgalatmospherepoint sourcesadditional physicsother instrumental effects We are working on all of these!

Halos in the Simulation

• Identify via HOP algorithm

• 12000 clusters at z=0 in simulation box above M = 5x1013Msolar

• Identify their locations in the 2d projection of the simulated survey

• Match to locations of halos provided by SExtractor

• Hallman et al. 2007

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Recall L. Verde’s talk

Stacking Caveats

• Stacking with a single simulation has problems

• Constant physical resolution (as f(z)) on the grid does not equal constant angular resolution on the sky

• Large scale correlations can be generated

• How can we solve that? Use multiple simulations!

The Big One(s)

• We are generating a complete, unique numerical simulation for each z

• Each simulation has a physical size specified by it’s angular extent at that redshift (ITC 10 degrees square).

• Allows lower computational effort for the most nearby volumes, since their physical resolution must be highest.

• Eliminates stacking issues (almost).• 2 cubic Gpc of total simulated volume

Plans for Huge LCs

• From smaller set of simulations, refine baryonic physics (cooling, star formation, SN feedback, AGN feedback, conduction, etc.)

• Vary cosmology (e.g., w, 8), determine precision necessary to distinguish

• Synthetic Observations (X-ray/SZE primarily) including both instrumental effects, backgrounds/foregrounds, etc.

Summary

• Survey yields depend on luminosity function, which depends on cosmology AND detailed baryonic physics AND dynamical states AND confusion, etc.

• If you want high precision, non-trivial problems in counting clusters

• Numerical N-body + hydro (!) simulations coupled with realistic synthetic observations allow us to understand systematics, get the “right” answer!

Sample Stacking Solution

Synthetic Observations

Constraints from Clusters, Dark Energy Equation of State

• Haiman et al 2001

Results from Adiabatic Physics Model (Projected Emission-Weighted Temperature)

5 Mpc