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“Observing Dark Energy”. Bob Nichol ICG, Portsmouth. SDSS, DES & WFMOS teams. Special thanks to Masao Sako, David Weinberg, Andy Connolly, Albert Stebbins, Rob Crittenden, Daniel Eisenstein, Josh Frieman, Tom Giannantonio, Ryan Scranton, Will Percival. Outline. Dark Energy Primer - PowerPoint PPT Presentation
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““Observing Dark Energy”Observing Dark Energy”
Bob NicholBob Nichol
ICG, PortsmouthICG, Portsmouth
Special thanks to Masao Sako, David Weinberg, Andy Connolly, Albert Stebbins, Rob
Crittenden, Daniel Eisenstein, Josh Frieman, Tom Giannantonio, Ryan Scranton, Will
Percival
SDSS, DES & WFMOS teams
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
Outline Dark Energy PrimerDark Energy Primer Growth of Structure: ISWGrowth of Structure: ISW Geometry: SN & BAOGeometry: SN & BAO
(DARK) MATTER
(DA
RK
) EN
ER
GY
CMB
SN
SNe and CMB force us into a Universe ~75% DE and ~25% DM. We are trace elements! Can this be true?
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
Understanding Dark EnergyUnderstanding Dark Energy
We can make progress on questions:• Is DE just a cosmological constant (w(z)=-
1)? (Make better observations and push to higher z)
• Is DE a new form of matter (with negative effective pressure) or a breakdown of GR?
(Study DE using different probes)
But there are only two broad avenues:• Geometrical tests (SN, BAO) • Growth of structure (CL, WL)
No compelling theory, so must be observational driven
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
““Massive Surveys”Massive Surveys”
SDSS: first “massive” survey ISW SDSSII SNe
Baryon Acoustic Oscillations (BAO)
DES: next “massive” imaging surveyThe power of photo-z’s
WFMOS: next “massive” redshift surveyThe power of spectroscopy
SDSSSDSSwww.sdss.orgwww.sdss.org
DR5: Million spectra, 8000 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 equation DE also effects the growth of structure i.e. Poisson equation with dark energy:with dark energy:
In a flat, matter-dominated universe (CMB tells us this), then In a flat, matter-dominated universe (CMB tells us this), then density fluctuations grow as:density fluctuations grow as:
Therefore, for a flat geometry, changes in the gravitational Therefore, for a flat geometry, changes in the gravitational potential are a direct physical measurement of Dark Energy as potential are a direct physical measurement of Dark Energy as they should be non-evolving if DE=0they should be non-evolving if DE=0
[ ])(4' 12DEma
d
dGk δρδρη
π +−=Φ −
€
δρm ∝ a
Experimental Set-upExperimental Set-up
Nolta et al, Boughn & Crittenden, Myers et al, Ashfordi et al, Fosalba Nolta et al, Boughn & Crittenden, Myers et al, Ashfordi et al, Fosalba et al., Gaztanaga et al., Rassat et al.et al., Gaztanaga et al., Rassat et al.
WMAP-SDSS WMAP-SDSS cross-correlationcross-correlation
WMAP W band
Luminous Red Galaxies (LRGs)
No signal in a flat, matter dominated Universe
ISW DetectedISW Detected 5300 sq degrees 5300 sq degrees Achromatic Achromatic
(no (no contamination)contamination)
Upto 5Upto 5 detection detection
Update of Scranton et al. 2003
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
Theoretical PredictionsTheoretical PredictionsW-band z=0.49 LRGs
m=0.3
m=0.2
Degeneracy between b, n(z) and cosmology
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
Giannantonio et al. 2006(astro-ph/0607572)
WMAP3-photoQSO
WMAP3 best fit
Detection of DE at z>1
0.075<0.075<mm<0.45<0.45-1.15<-1.15<ww<-0.76<-0.76
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
Evolution of DEEvolution of DEw=-1 survives w=-1 survives another (weak) another (weak)
testtest
But rules out models But rules out models with with DD(z=1.5) > (z=1.5) >
0.50.5
Important for tests Important for tests of modified gravity of modified gravity
theories theories
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
• bridge low-z (z<0.05; bridge low-z (z<0.05; LOSS, SNF) and high-z LOSS, SNF) and high-z (0.3<z<1.0; ESSENCE, (0.3<z<1.0; ESSENCE, SNLS) sourcesSNLS) sources
• understand and understand and minimize systematics of minimize systematics of SN Ia as distance SN Ia as distance indicators (look at indicators (look at correlations with host correlations with host galaxy properties)galaxy properties)
SDSSII SNe SurveySDSSII SNe SurveyExploring DE & SNe at an epoch when DE dominates
Riess et al. (2004)compilation
Astier et al. (2005)
9% measurement of w by 2008 comparable with SNLS
6% measurement of w when combined with SNLSEspana-Bonet, Nichol, Ruiz-Lapuente
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
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• ““Stripe82” (UKIDSS data)Stripe82” (UKIDSS data)
Survey AreaSurvey Area
N S
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
• Color-type SNe candidates using nightly g r i data
• fit light-curve for redshift, extinction, stretch for Ia
• Able to type with >90% efficiency after ~2 - 4 epochs
Photometric TypingPhotometric Typing
IaIa
II
SN2005hy
II
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
• 332 spectroscopically confirmed SN Ia
• 254 unconfirmed Ia’s with good LC’s (galaxy redshifts exist for 60)
• Many Ia’s now have multi-epoch spectra
• Follow-up on NTT, WHT, Subaru, ARC3.5m, HET, MDM
• One more season, expecting over 500 SNe
International Follow-upInternational Follow-up
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
2005
spe
ctro
scop
ical
ly c
onfi
rmed
+ p
roba
ble
SN
Ia
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
dispersion ~ 0.18 maginternal consistency
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
Galaxy-SNe CorrelationsGalaxy-SNe Correlations
Baryon OscillationBaryon Oscillation
o Gravity squeezes the gas, pressure pushes back! Gravity squeezes the gas, pressure pushes back! They oscillateThey oscillate
o 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 i.e. the CMB!• That was the Universe at 400,000 years. Can we see these sound waves today?
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
BAO 2006BAO 2006(Percival et al. 2006)(Percival et al. 2006)
WMAP3
SDSS DR5 520k galaxies
m=0.24 best
fit WMAP model
Miller et al. 2001, Percival et al. 2001, Tegmark et al. 2001, Cole et al. 2005, Eisenstein et al. 2005, Hutsei 2006, Blake et al. 2006, Padmanabhan et al. 2006
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
Smooth + sinc function(Blake & Glazebrook 2003)
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
One One parameteparamete
r r Standard ruler(flat,h=0.73,b=0.17)
Percival et al. 2006
Best fit m=0.2699.74% detection (3)
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
mm - h Degeneracy - h Degeneracy
h=0.72±0.08 HST
m=0.256+0.049-
0.029
m0.275h WMAP3
m=0.256+0.029-
0.024
mh2 WMAP3
m=0.256+0.019-
0.023
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
SummarySummary
ISW detected at several redshifts to z~1 and consistent with cosmological constant.
Good news for people looking for DE at high zGood news for people looking for DE at high z 229 SDSS SNIa’s so far, 400 by 2007
Systematics limited and will deliver w to 6% BAO have been detected at 3
m=0.256 to 10% from acoustic scale
Good news for future BAO experiments
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
Future ExperimentsFuture Experiments(Stage III)(Stage III)
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
Dark Energy Survey Dark Energy Survey (DES)(DES)
• 5000 sq deg multiband (g,r,i,z) survey of SGP using CTIO Blanco with a new wide-field camera
• 40 sq deg time domain search for SNe
1. Cluster counts from optical+SPT2. Weak lensing maps3. SNe Ia distance measurement study from 2000 Sne
I. Unable to gain spectroscopic follow-up for all these Sne. Must use photometric classifications and redshifts
II. Use SDSSII as a “training sample” to prepare for DES
4. Galaxy angular power spectrum for 300 million galaxies I. Baryon Acoustic Oscillations from photo-z’s
Each will independently constrain the dark energy eqn of state <10%
DES on-sky by 2009DES on-sky by 2009
The Dark Energy Survey The Dark Energy Survey UK Consortium UK Consortium
(I) PPARC funding: O. Lahav (PI), P. Doel, M. Barlow, S. Bridle, S. Viti, J. Weller (UCL), R. Nichol (Portsmouth), G. Efstathiou, R. McMahon, W. Sutherland (Cambridge), J. Peacock (Edinburgh) Submitted a proposal to PPARC in February 2005 requesting
£ 1.5 M for the DES optical design. In March 2006, PPARC Council announced that it “will seek participation in DES”.
(II) SRIF3 funding: R. Nichol, R. Crittenden, R. Maartens, W. Percival (ICG Portsmouth) K. Romer, A. Liddle (Sussex)
Funding the optical glass blanks for the UCL DES optical work
These scientists will work together through the UK DES Consortium and are collaborating with the Spanish DES Consortium
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
ANNz: Collister & Lahav 2005, Abdalla et al.
DES Photo-z’sDES Photo-z’sDES science relies on good photometric
estimates of the 300 million expected galaxies
Simulated DES
Simulated DES+VISTA
griz
grizJKu-band from VST could remove the
low-z errors(ugrizJK)
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
• Give photo-z’s to z~2 with < 0.1
• BAO improves by 50% with VISTA; 15% error on w just the BAO scale
• Targets for Gemini, VLT
• Overlap with CLOVER, SPT
DES + VISTA + VSTDES + VISTA + VST
DES + Planck ISW will be better than LSST for
non-constant w models(Pogosian et al. 2005)
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
WFMOSWFMOS• Proposed MOS on Subaru via
an international collaboration of Gemini and Japanese astronomers
• 1.5deg FOV with 4500 fibres feeding 10 low-res spectrographs and 1 high-res spectrograph
• First-light in 2013• ~20000 spectra a night
(2dfGRS at z~1 in 10 nights)• DE science, Galactic
archeology, galaxy formation studies and lots of ancillary science from database
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
z~1 survey with 2 million
galaxies with twice LRG
volume
1% accuracy
KAOS purple book (Seo, Eisenstein, Blake, Glazebrook)
WFMOS will measure w to <4% and dw/dz to <15%
Distance ScaleDistance Scale
August 1st 2006August 1st 2006 Durham "Cosmic Frontiers"Durham "Cosmic Frontiers"
Testing Modified Testing Modified GravityGravity
DGPLCDM
7 difference
Yamamoto et al. 2006
Summary IISummary IIa) Experiments by 2010 will measure w
(constant) to a few %, but that doesn’t mean we understand it!
b) Next generation surveys will probe w(z) and start testing “growth of structure” measurements of DE