““The Dark Side of The Dark Side of the SDSS”the SDSS”

Bob NicholBob Nichol

ICG, PortsmouthICG, Portsmouth

Chris Miller, David Wake, Brice Menard, Idit Zehavi,

Ryan Scranton, Gordon Richards, Daniel Eisenstein,

all my SDSS colleagues

OutlineOutline

• Brief overview of the SDSSBrief overview of the SDSS• New paths to the “Dark Side”New paths to the “Dark Side”

ISW effectISW effect Cosmic magnificationCosmic magnification Baryon Acoustic OscillationsBaryon Acoustic Oscillations

• WFMOSWFMOS

SDSSSDSS

DR4: 849,920 spectra, 6670 sq degs

Extension (2005-2008): Legacy, SNe, Galaxy

Late-time Integrated Late-time Integrated Sachs Wolfe (ISW) EffectSachs Wolfe (ISW) Effect DE also effects the growth of structure i.e. Poisson DE also effects the growth of structure i.e. Poisson

equation with dark energy:equation with dark energy:

In a flat, matter-dominated universe (CMB tells us this), In a flat, matter-dominated universe (CMB tells us this), then density fluctuations grow as:then density fluctuations grow as:

Therefore, for a flat geometry, changes in the Therefore, for a flat geometry, changes in the gravitational potential are a direct physical gravitational potential are a direct physical measurement of Dark Energymeasurement of Dark Energy

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dGk δρδρ

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δρm ∝ a

Experimental Set-upExperimental Set-up

See also: Nolta et al, Boughn and Crittenden, Myers et al, Ashfordi et See also: Nolta et al, Boughn and Crittenden, Myers et al, Ashfordi et alal

ISW and the SDSSISW and the SDSS Searching for a detectionSearching for a detection

LRG selection to z~0.8 LRG selection to z~0.8 (Eisenstein et al. 2001)(Eisenstein et al. 2001)

5300 sq degrees 5300 sq degrees Achromatic (no Achromatic (no

contamination)contamination) Errors from 5000 CMB skiesErrors from 5000 CMB skies Compared to a null result Compared to a null result

>95% for all samples>95% for all samples Data prefers DE model over Data prefers DE model over

null hypothesis at the >99% null hypothesis at the >99% confidence for all confidence for all combinationscombinations

Yellow: “smoothed clean”, Black: “Clean”, Red: Q, Blue: W, Green: V

Future ISW directionsFuture ISW directions Probe of DE sound speed (Hu & Scranton 2004; Pogosian 2004) and Probe of DE sound speed (Hu & Scranton 2004; Pogosian 2004) and

highly complementary to geometrical measures of DEhighly complementary to geometrical measures of DE Circa 2006 (SDSS)Circa 2006 (SDSS)

8000 sq degrees 8000 sq degrees (≥3(≥3 per redshift) per redshift)

Tighter redshift intervals Tighter redshift intervals (> 5 bins)(> 5 bins)

BeyondBeyond ASTRO-F all-sky out to z~1.5ASTRO-F all-sky out to z~1.5 UKIDSS+VISTA all-sky (LRG selection to z>1)UKIDSS+VISTA all-sky (LRG selection to z>1) QSO catalogs (z out to 3)QSO catalogs (z out to 3) DES & LSST will provide competitive DE constraints from ISW for DES & LSST will provide competitive DE constraints from ISW for

Kink models of DE (Pogosian et al. 2005)Kink models of DE (Pogosian et al. 2005)

Cosmic MagnificationCosmic Magnification

Gravitational magnification increases flux received from galaxies and hence allows us to see fainter galaxies, resulting in an increased apparent galaxy number

density. But, it also magnifies the solid angle of the projected lensed sky which results in a decrease in the apparent galaxy number density. Therefore a

competition between the two!

more flux

more solid angle

more sources come in than area diluted: positive positive correlationcorrelation

less sources come in than area diluted: negative correlationnegative correlation

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Hunting for quasarsHunting for quasars

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are needed to see this picture.

Traditional UVX approach to finding quasars uses hyper-planes (Richards et al. 2002). However, significant contamination (~40%), thus demanding spectroscopic follow-up. New bayesian technique provides <5% contamination (Richards et al. 2004): photometric QSO catalogs

Blue points = dataBlack line = best fitRed line = best fit + alphaGrey shading = 1sigma

195,000 quasars13.5 million

galaxies

8 detection

Now fully consistent with CDM model

Ideal for next generation imaging surveys like DES

Baryon Acoustic Baryon Acoustic OscillationOscillation

Gravity squeezes the gas, pressure pushes back. Gravity squeezes the gas, pressure pushes back. They oscillateThey oscillate

When the Universe cools below 3000K, these When the Universe cools below 3000K, these baryonic acoustic oscillations are frozen in baryonic acoustic oscillations are frozen in

Courtesy of Wayne Hu

BAO observationsBAO observations Effect of these oscillations already seen in the CMB Can we see them today in the distribution of galaxies?

LRG

LRG Correlation FunctionLRG Correlation Function

The correlation function is the probability of finding pairs at a given separation, above that of a random distribution.

Excess of galaxies separated by 500 million

light years

What does it mean?What does it mean? We have detected the BAO at two different epochs consistent with our theory of gravitational structure formation BAO provide a fixed scale, or “standard ruler” BAO are consistent with LCDM model Assuming LCDM model, then BAO constrain flatness of universe to 1% - break the degeneracy between w & curvature

WFMOSWFMOS3000 thousands of fibers over a 1.5 degree field-of-view on an 8-meter class telescope

(Subaru/Gemini)z~1 survey with

2 million galaxies with

twice LRG volume

1% accuracy

Taken from WFMOS Feasibility Study by NOAO, JHU, AAO, Oxford, Durham, Portsmouth, UATaken from WFMOS Feasibility Study by NOAO, JHU, AAO, Oxford, Durham, Portsmouth, UA

w ~ 5%dw/dz ~ 20%

WFMOS will also be a user instrument and have significant archival value-added science eg. Baldry et al. (2004) SDSS color bimodality as fn(L,ρ at z~1

mod = 5 + L/L-20

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