Surveying the Surveying the Universe with Universe with

SNAPSNAP

Tim McKayUniversity of Michigan Department of Physics

Seattle AAS Meeting: 1/03For the SNAP collaboration

The Supernova/Acceleration ProbeThe Supernova/Acceleration Probe

• Mostly pure survey mode

• Step and stare across the sky, each location seen in all nine filters

• Dithered exposures at each location

• Two surveys: a deep, time domain SNe survey and wide single pass weak lensing survey

A space based optical/near-IR survey telescope

Large field of view coupled with 0.1” resolution and broad coverage

SNAP Deep & Time Domain SurveySNAP Deep & Time Domain Survey

• Base SNAP survey: 15 square degrees near ecliptic poles

• ~6000x as large as ACS deep field, to mAB=30.4 in nine optical and IR bands

• Provides ≥ 100 epochs over 16 months (each to mAB=27.8) for time domain studies in all nine bands

GOODS Survey area

Hubble Deep Field

SNAP Wide Weak Lensing SurveySNAP Wide Weak Lensing Survey

• ~300 square degree ‘wide’ survey surrounding each of the deep fields

• Roughly five months of observing time

• Four dithered 500 second exposures at each location; sensitive to mAB=28.1

• Every field observed in all nine optical NIR filters

GOODS Survey area

Hubble Deep Field

SNAP imaging surveys are uniqueSNAP imaging surveys are unique

• Depth —From the disk to z=10

—Depth in the time domain; R~27.8 in each epoch

• Optical + NIR—9 bands = Low resolution

spectroscopy (R~7)

—Available in time domain

—NIR follows Lyman- emission to z=12

• Image quality—High resolution

—PSF stability

• Photometric stability

Some of the topics impacted:1. Galaxy studies: evolution

and clustering, a census of R, I, z, and J band dropout galaxies

2. Galaxy clusters: identification of high redshift galaxy clusters, faint and small constituents

3. High-z quasar studies: mapping the quasar luminosity function to z=10, probing the structure of reionization

4. Transients; GRBs, QSO/AGN, outer solar system objects

5. Cool stars in the Milky Way6. Lensing: evolution of the

galaxy-mass correlation to z=1, cluster masses, etc.

7. Targets: Identification of targets for JWST, CELT, etc…

Galaxy evolution and photo-zGalaxy evolution and photo-z

• HDF’s illustrate the potential impact of SNAP studies

• Large area observations required to probe environmental effects at each redshift

• High resolution for structure and population studies

• Photo-z: —4000Å break for z=0-3.0—Ly- break for z=3.3-12—NIR for dust and high z

• ≥5x107 galaxies with photoz

Family of Galaxy Spectra: Budavari et al.

Simulated SNAP Photo-zSimulated SNAP Photo-z

• Expected photo-z performance for SNAP multiband survey is excellent (z~0.04/galaxy)

• Spatially resolved color gives photo-z + stellar population information

Conti & Connolly: Jan. 2002 AAS

Spectroscopic z

Pho

tom

etric

z

Single band image SFR per pixel

Linear survey size (h-1 Mpc)

J. Colberg, VIRGO simulations: Jenkins et al, 1998 ApJ,499,20-40

Evolution of Galaxy ClusteringEvolution of Galaxy Clustering

• Photo-z defines redshift sheets

• Evolution of 2D clustering• 12 nearly independent

redshift sheets from z=0-3• Optical/NIR covers

restframe optical out to z=3, simplifying evolution studies

• Wide fields substantially reduce sensitivity to cosmic variance constraints

Conti and ConnollyJan 2002 AAS

Rel

ativ

e E

rror

10%

Finding clusters in SNAP dataFinding clusters in SNAP data

• Important markers of structure formation which form relatively late.

• dn/dz exquisitely sensitive to cosmology; alternate dark energy probe?

• Widefield multicolor CCD data has revitalized optical cluster finding—Cluster members are the

reddest galaxies at each redshift

—Clusters in position-color space

Z=0.165

SDSS image of Abell 1553

Identification of high-z clustersIdentification of high-z clusters

• Clustering in position-color space essentially eliminates contamination by projection

• Gladders & Yee (2000), Goto et al. (2001), Annis et al. (2002)

• E/SO ridgeline provides extremely accurate (z0.01) photometric redshift

• Red sequence in place at z>1

Red sequence galaxies at z=1.27(van Dokkum et al, 2000)

i magnitude

g-r

colo

r

E/SO ridgeline

Z=0.041

Z=0.138

Z=0.277

Z=0.377

Example color cluster images from the SDSS

Expected SNAP cluster countsExpected SNAP cluster counts

15 square degree survey still suffers from cosmic variance. 300 square degree lensing survey will be more useful for cluster counts

Based on Virgo consortium Hubble Volume CDM Simulations

N (

M>

5x1

013 M

) in

15

sq. d

eg

.

Redshift in bins of 0.02

z=1

z=2

z=3

Quasar evolution to z>12Quasar evolution to z>12

• Quasar identification through multicolor observations

• Further selection through variability

• Good QSO redshift estimates through photoz

• Depth extends to 1000x less luminous objects

• NIR extends to much higher redshift (from 6.3-12)

SDSS QSO color selection

Fan et al., AJ, 2000

Setting up reionization probesSetting up reionization probes

• Highest redshift SDSS QSO’s show evidence for Gunn-Peterson absorption associated with neutral IGM

• Possibly seeing edge of reionization epoch

• Structure in reionization is unknown: caused by variations in UV flux from early stars + quasars

• SNAP discovered z>6 QSO’s, with NGST spectroscopy, can map the spatial structure of reionization

Pentericci et al, 2001z=6.3 quasar

Fan et al., 2002

Gun

n-P

eter

son

Opt

ical

De

pth

Redshift

Wavelength

f (e

rg c

m-2

s-1 A

-1)

Quasar number countsQuasar number counts

X. Fan, based on SDSS QSO LF

Z > 5Z > 7.5

Z > 10One in SNAP deep survey

AB magnitude

Qua

sars

per

squ

are

degr

ee

SNAP high-z weak lensing studiesSNAP high-z weak lensing studies

• Beyond cosmology: galaxy and cluster studies

• To measure lenses at z=1.0 requires many sources at z~3.0

• Ground based studies resolve galaxies to R~25, this limits available sources

• To study lenses at and beyond z=1 requires space based NIR observations —Evolution of galaxy-

mass correlation function

—Mass selected galaxy cluster number density and clustering

—Mass maps of filaments

Why go so faint?Why go so faint?

Basic geometry is similar for the three surveys.

Sensitivity changes due to available source density.

Lensing S/N is much higher for a deeper space based survey.

Sensitivity tilted to low-z.

25

2830

SNAP Surveys and NG TelescopesSNAP Surveys and NG Telescopes

• Wide area surveys have always fed massive spectroscopic instruments—Palomar 48” >

200”—SDSS > 8-10m’s—SNAP > JWST,

CELT and other next generation ground-based telescopes

• Biggest HST deep survey will be ACS survey:—6300x smaller than

SNAP main survey—About as deep

• SNAP NIR survey capabilities especially important