DES Cluster Simulations and the ClusterSTEP

ProjectM.S.S. Gill (OSU / CBPF / SLAC)

In collaboration with: J. Young, T.Eifler, M.Jarvis, P.Melchior and other DES members

Pixels to Shears Workshop, University of Edinburgh

Friday, Jan 28, 2011

Our first ‘end-to-end’ DES simulations results from full analysis of a SIS simulated cluster

Progressing next to: ClusterSTEP

More complex ray-traced simulation

Higher statistics

Includes: PSF variation, seeing levels

Will be publically released 2

II. The Dark Energy Survey (DES) Cluster Simulations

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DES: Probe the nature of dark energy with• Supernovae• Baryon oscillations• Clusters of galaxies• Weak gravitational lensing

Our Initial DES Cluster Simulation

All 62 chips are simulated (H. Lin and N. Kouropatkin)Stepped up in increasing complexity:Start with just background galaxiesAdd in shearAdd in noiseAdd in psfAdd in starsAdd in cluster and foreground galaxiesPublically available to all at: ccapp.osu.edu/DEScluster

(See Gill et al. 2009,  arXiv:0909.3856 )

CLUSTER IMAGE INFORMATION

Truth Table Information contains: (RA, DEC) and (x,y) pixel positions for each object Redshift of galaxy objects grizy Magnitudes Theoretical shear for galaxy object positions

Image (only in one band): Corresponds to truth r Magnitude Theoretical shear convolved with intrinsic object ellipticity

Shear applied only for gamma < 0.2 (beyond ~400 pixels = 80” = 72 kpc for z=0.3), to avoid strong lensing

regime. Full plane radius: ~15k pixels (pixelscale=0.27”/pixel)

[ Cluster simulation made by H. Lin and N. Kourapatkine at FNAL]

APPLIED CLUSTER SHEAR

DES Full plane: averages of truth shears in cells inside of each CCD. Each CCD is split into equally sized 8x4 cells.

Same thing but close up on cluster center

pixels

pixels

Input: sigma_v = 1250 km/sec

SIMULATED IMAGES

Low Noise

No Noise

High Noise

Stars +BkgdGals

All images here show same part of CCD 28 – containing cluster center

Stars +BkgdGals

Stars +BkgdANDFrgndGals

Stars +BkgdANDFrgndGals

SIS Fits to the DES simulation

Screen clipping taken: 2/17/2009, 2:43 AM

                                                                                                                                          

After PSF correction, shear matches truth within error

Fit to SExtractor ellip = pink solid

Truth fit = red solid

Fit to extracted ellip. = dashed

Shear vs. radial distance from center in pixels

Each cyan or red point representsone galaxy with its ‘observed’ellipticity – an unbinned fit is thendone to these points

Results: E-mode PROFILESUsing r-i>0.6 Color Cut Files z = 0.8z = exact

1091386Z = EXACTSHAPELETS

661211Z = EXACTIMCAT

1.51252.8Z = EXACTTRUTH

841299Z = 0.8SHAPELETS [ RJM et al. ]

601168Z = 0.8 IMCAT

0.81212.7Z = 0.8TRUTH

UncertaintyσvREDSHIFT CORRECTION

FILE # sigma away

Many1.51

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1.5

Fit OutputLow NoiseFile, bkgd gals pickedby color

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Moving to ClusterSTEP - Goals• To extend results of STEP to high shear regime as would be found near clusters (g~0.1-0.15 vs. g<~ 0.05 in STEP) -- const shear images also being made

• To compare performance of modern pipelines on cluster images and see how errors in shape measurement propagate to final mass estimate

• To performing tests under different variations: e.g. noise level, PSF model, galaxy selection in simulated images (cf. van Waerbeke 2001ish)

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Making ClusterSTEP Images

• Start from R. Wechsler et al.’s full-scale N-body cosmological simulations for DES

•Ray-trace so that shear naturally follows properly from realistic cluster profiles

•Resulting shear is then applied back to galaxies in images

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Example of shear results from full DECam plane

Colored symbols are clusters (color redshift, size mass)

Shear map is from truth info here

This is old, get halo 2 or 6, we’ll pick justOne per image, only selected ones areGood according to Matt

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Typical realistic DECam focal plane PSF

New ones will have higher corner PSF, with ellipticity up to 0.05, may be more complex also (atm turbulence would do this)

Here: Longest whiskers are e ~ 0.01

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Variation of results with PSF variation

IMCATVs. TruthFitsshown

Conclusions and Next StepsAble to robustly reconstruct input velocity dispersion in initial simulation

Now moving to more realistic ClusterSTEP images with ray-tracing

Will get more robust answers for variation of cluster mass with differing observational conditions/cuts

Eventually plan to open this to public participation

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Thx for organizing a “GREAT” workshop! :->

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Click to edit Master text stylesSecond level

Third level Fourth level

Fifth level

In Bonny Ole Scotland !

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Extra Slides

SIMULATION FILES SUITEAcronym

File Description

Noise Shear Contents

OF Original Nonsheared

None None Background Galaxies

SF Sheared None Cluster Shear

Background Galaxies

NF Noise-added High Cluster Shear

Background Galaxies

HPF HN PSF-added High Cluster Shear+ PSF

Background GalaxiesStars

HFF HN Foreground Galaxies Added -- like a 600 sec DES exposure

High Cluster Shear+ PSF

Background GalaxiesStarsForeground Galaxies

LPF LN PSF-added Low Cluster Shear+ PSF

Background GalaxiesStars

LFF LN Foreground Galaxies Added

Low Cluster Shear+ PSF

Background GalaxiesStarsForeground Galaxies

Most realistic images are in red; Noise: LN ~ 1/13 * HN

Full Field Simulation

Model psfFrom stars(Imcat)

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Individual galaxies inside the clusters

Degrees (RA)

Degrees

(Dec)