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

Bob NicholBob Nichol

ICG, PortsmouthICG, Portsmouth

Thanks to all my collaborators on SDSS

and other teams

OutlineOutline

• A A veryvery brief overview of Dark Energy brief overview of Dark Energy• A A veryvery brief overview of the SDSS brief overview of the SDSS• SDSS searches for the “Dark Side”SDSS searches for the “Dark Side”

SDSS SNeSDSS SNe ISW effectISW effect Cosmic magnificationCosmic magnification Baryon acoustic oscillations (BAO)Baryon acoustic oscillations (BAO)

• Future experimentsFuture experiments

WMAP: Universe at 380,000 yrs

Largest oscillations that are causally connected

(DARK) MATTER

(DA

RK

) EN

ER

GY

CMB

SN

SNe and CMB force us into a Universe ~75% DE and ~25% DM. But is this true?What is DE?

Understanding Dark EnergyUnderstanding Dark Energy(The billion dollar question)

To confirm DE we need to observe it in as many ways as possible, but there are only two broad avenues:• Geometrical tests (distances, volumes)• Growth of structure (cluster counts)

To determine what DE is, we can make progress on two simple questions:• Is DE just a cosmological constant (w(z)=-1)?

(Push observations to higher redshifts)• Is DE a new form of stress-energy with

negative effective pressure or a breakdown of General

Relativity at large distances? (Study DE using different probes)As we don’t know much, all observations are important

Fairbairn & Goobar 2005

DGP model for 5D gravity

Also, Sawicki & Carroll (2005) & Koyama (2006) show there are noticeable differences in the evolution of structure in DGP models. This maybe testable!

DGP CosmologiesDGP Cosmologies

SDSSSDSS

DR4: 849k spectra, 6670 sq degs

Done 07/2005: ~700,000 redshifts, 8000 sq degs

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

• Type Ia supernovae (SNe)Type Ia supernovae (SNe)

• spectroscopically confirm spectroscopically confirm and obtain “well-measured” and obtain “well-measured” light curves of ~200 SN Ia light curves of ~200 SN Ia from z = 0.05 to ~ 0.4from z = 0.05 to ~ 0.4

• bridge low-z (z<0.05; LOSS, bridge low-z (z<0.05; LOSS, SNF) and high-z (0.3<z<1.0; SNF) and high-z (0.3<z<1.0; ESSENCE, SNLS) sourcesESSENCE, SNLS) sources

• understand and minimize understand and minimize systematics of SN Ia as systematics of SN Ia as distance indicatorsdistance indicators

• SN Ib/c, II, rare typesSN Ib/c, II, rare types

• Other transientsOther transients

SDSSII SNe SurveyExploring DE & SNe at an epoch when DE dominates

Riess et al. (2004)compilation

Astier et al. (2005)

Use the SDSS 2.5m telescopeUse the SDSS 2.5m telescope• September 1 - November 30 of 2005-2007September 1 - November 30 of 2005-2007• Scan 300 square degrees of the sky every 2 daysScan 300 square degrees of the sky every 2 days• discover supernovae and obtain multi-color light discover supernovae and obtain multi-color light

curvescurves

Survey AreaSurvey Area

N S

ARCHETMDMWHT

Subaru(NTT)

Follow-up

• Color-type SN candidates using nightly g r i data:

• make template light curves from multi-epoch spectra (Peter Nugent) and other sets of spectra of well-observed historical SNe (SUSPECT database)

• Ia, Ia-pec, II-P, II-L, IIb, Ibc, Ibc-hypernova

• fit for redshift, extinction, stretch for Ia

• Able to type with >90% efficiency after ~2 - 4 epochs

Photometric TypingPhotometric Typing

Ia Ia II

SN2005hy

II

Team of 15 “hand-scanner” visually inspected 144,000 Team of 15 “hand-scanner” visually inspected 144,000 objects selecting nearly 10k SN targets!objects selecting nearly 10k SN targets!

• 126 spectroscopically confirmed SN Ia

• 13 spectroscopically probable SN Ia

• 6 SN Ib/c (3 hypernovae)

• 10 SN II (4 type IIn)• 5 AGN• ~hundreds of other

unconfirmed SNe with good light curves (galaxy spectroscopic redshifts measured for ~25 additional Ia candidates)

• Focused primarily on Ia

Results from 2005Results from 2005

<z> = 0.21

2005

spe

ctro

scop

ical

ly c

onfi

rmed

+ p

roba

ble

SN

Ia

PreliminaPreliminaryry

No reddeningNo reddening=0.27=0.27

Important training set for next Important training set for next generation of imaging surveys e.g. generation of imaging surveys e.g. DES will detect 3000 SN by ~2010DES will detect 3000 SN by ~2010

w) = 0.1 from w) = 0.1 from SDSS+ESSENCE+WMAP+LSS (statistical SDSS+ESSENCE+WMAP+LSS (statistical

errors only, constant w, flat Universe)errors only, constant w, flat Universe) SDSS data on host galaxies will allow SDSS data on host galaxies will allow study the scattering in this relation in study the scattering in this relation in

greater detailgreater detail

Lambda = 0.74

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 Energy as they should be non-measurement of Dark Energy as they should be non-evolving if DE=0evolving if DE=0

[ ])(4' 12DEma

d

dGk δρδρη

π +−=Φ −

€

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

WMAP vs SDSSWMAP vs SDSS

WMAP W band temperatures across 50% of SDSS areaWMAP W band temperatures across 50% of SDSS area

Density of Luminous Red Galaxies (LRGs) selected from the SDSSDensity of Luminous Red Galaxies (LRGs) selected from the SDSS

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 contamination)Achromatic (no contamination) Errors from 5000 CMB skiesErrors from 5000 CMB skies Compared to a null resultCompared to a null result

>95% for all samples>95% for all samples Low redshift sample Low redshift sample

contaminated by starscontaminated by stars Individually >2Individually >2 per redshift per redshift

sliceslice 4 redshift shells (not 4 redshift shells (not

significant overlap)significant overlap)

Yellow: “smoothed clean”, Black: “Clean”, Red: Q, Blue: W, Green: V Overall, we have detected signal at 5

ISW PredictionsISW Predictions

Halo model. Halo model. Biasing of Biasing of b=1,2,3 & 4 for LRGsb=1,2,3 & 4 for LRGs

Plus SZ on small scalesPlus SZ on small scales Data prefers DE model Data prefers DE model

over null hypothesis at over null hypothesis at the >99% confidence the >99% confidence for all combinationsfor all combinations

The measurement is The measurement is very sensitive to n(z) very sensitive to n(z) assumed and assumed and mm

Scranton et al 2003Scranton et al 2003

Future ISW directionsFuture ISW directions dg/dz is a very powerful probedg/dz is a very powerful probe Only probe of DE clustering (Hu & Only probe of DE clustering (Hu &

Scranton 2004; Pogosian 2004) and Scranton 2004; Pogosian 2004) and highly complementary to geometrical highly complementary to geometrical measures of DE (SNe etc)measures of DE (SNe etc)

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(>4.5(>4.5 detection if there!) detection if there!)

UKIDSS+VISTA all-sky (LRG UKIDSS+VISTA all-sky (LRG selection to z>1)selection to z>1)

QSO catalogs (z out to 3)QSO catalogs (z out to 3) Cooray, Huterer, Baumann 2003

Dark Energy Survey Dark Energy Survey (DES)(DES)

5000 sq deg multiband survey of SGP using CTIO, 40 sq deg time domain search for SNe The survey will study the expansion history of the universe and

the growth of density perturbations using four distinct techniques: 1. 4000 sq deg survey in collaboration with the SPT2. weak lensing study3. galaxy angular power spectrum distance measurement study4. SNe Ia distance measurement study

Each will independently constrain the dark energy eqn of state ~10%

ISW with DES+Planck is as good as SNAP for non-constant w (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 diluted

less source

come in than

diluted

Effe

cts

can

cel

Hunting for quasarsHunting for quasarsQuasi-stellar sources: by definition they look like stars!

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Traditional approaches have used UVX approach to finding quasars, i.e., quasars are “very blue” so can be isolated in color-color space using simple hyper-planes (see Richards et al. 2002). However, there is significant contamination (~40%), thus demanding spectroscopic follow-up which is very time-consuming.

Probabilistic approachProbabilistic approach Use Kernel Density Estimation (KDE) to map color-color space

occupied by known stars and quasars (“training sets”) Use cross-validation to “optimal” smooth the 4-D SDSS color

space and obtain PDFs Fast implementation via KD-trees (Gray & Moore) ~16,000 known quasars and ~500000 stars Using a non-parametric Bayes classifier (NBC)

additional cut

95% complete95% pure

Stars

QSOs

F stars

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

195,000 quasars13.5 million

galaxies

8 detection

Now fully consistent with LCDM

Baryon OscillationBaryon Oscillation

• 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 sound waves are frozen in sound waves are frozen in

Courtesy of Wayne Hu

Cosmic Microwave Cosmic Microwave BackgroundBackground

Effect of this sound wave already discovered in relic light of the early universe That was the Universe at 400,000 years. Can we see these sound waves today?

700,000 light years

500 Million Light Years

Credit: SDSSA slice of the SDSS

The Correlation FunctionThe 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 sound wave in the Universe at two very different epochs (400,000 yrs after Big Bang and present-day). This is important because our theory of gravitational structure formation predicts that such features should have been preserved. Detecting the sound wave in the galaxies is the “SMOKING GUN” that our theory is correct. Better yet, the sound wave is an object of fixed size, a “standard ruler” or “cosmic yardstick”. This means that we can measure its apparent size anywhere in the Universe, and determine how far it is away because we know its true size.

FLAT GEOMETRYCREDIT: WMAP & SDSS websites

CM

B

Looking back in time in the Universe

FLAT GEOMETRY

SD

SS

GA

LAX

IES

Looking back in time in the Universe

FLAT GEOMETRYCREDIT: WMAP & SDSS websites

SD

SS

GA

LAX

IES

CM

B

Looking back in time in the Universe

OPEN GEOMETRY

Looking back in time in the Universe

FLAT GEOMETRYCREDIT: WMAP & SDSS websites

CM

B

Looking back in time in the Universe

CLOSED GEOMETRY

SD

SS

GA

LAX

IES

UNIVERSE IS FLAT TO 1% UNIVERSE IS FLAT TO 1% PRECISIONPRECISION

WFMOSWFMOSA quantum leap in spectroscopic efficiency.

Thousands of fibres over a 1.5 degree field-of-view on an 8-meter class telescope: over an order of over an order of magnitude increase in mapping efficiency of 2dFmagnitude increase in mapping efficiency of 2dF

z~1 survey with 2 million

galaxies with twice LRG

volume

1% accuracy

KAOS purple book (Seo, Eisenstein, Blake, Glazebrook)

Will get w to <5% and w’ to <20%

ConclusionsConclusions SDSS continues for 3 more years and has been successful in SDSS continues for 3 more years and has been successful in

finding many hundreds of SNe.finding many hundreds of SNe.

The quality and quantity of SDSS data has provide several The quality and quantity of SDSS data has provide several complementary detections of dark energy and dark matter, complementary detections of dark energy and dark matter, e.g., the ISW effect provided direct physical evidence that DE e.g., the ISW effect provided direct physical evidence that DE existsexists

Detected cosmic magnification and consistent with LCDM. Detected cosmic magnification and consistent with LCDM. Powerful new probe of the UniversePowerful new probe of the Universe

SDSS has detected the baryon oscillations in the local SDSS has detected the baryon oscillations in the local Universe, the “missing link” between CMB and LSS. Now have Universe, the “missing link” between CMB and LSS. Now have a “standard ruler”a “standard ruler”