Observational Cosmology

Tom Shanks

Durham University

Summary

• Review observational evidence for standard cosmological model - CDM

• Then review its outstanding problems - astrophysical + fundamental

• Briefly look at difficulties in finding an alternative model

• Conclude - whether CDM is right or wrong - its an interesting time for cosmology!

Observational cosmology supports CDM!

• Boomerang + WMAP CMB experiments detect acoustic peak at l=220(≈1deg)

• Spatially flat, CDM Universe (de Bernardis et al. 2000, Spergel et al 2003, 2006)

• SNIa Hubble Diagram requires an accelerating Universe with a cosmological constant,

• CDM also fits galaxy and QSO clustering results (e.g. Cole et al 2005)

WMAP 3-Year CMB Map

WMAP 3-Year Power Spectrum

Spatially flat, (k=0) universe comprising:

~72% Dark Energy

~24% CDM

~4% Baryons

(Hinshaw et al. 2003, 2006, Spergel et al. 2003, 2006)

• SNIa 0.5mag fainter than expected at z~1 if m=1

• Universe flat (k=0) + accelerating with ~0.7

• Vacuum/ Dark energy eqn of state

Supernova Cosmology

Credits: ESSENCE+ Supernova Legacy Survey + HST Gold Sample

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AAT 2dF Redshift Surveys

• 2dF ~400 fibres over 3deg2 -50 x bigger field than VLT vs 4x smaller mirror

• 2dF galaxy and QSO z survey clustering also supports CDM

2dF Galaxy Redshift Survey

2dFGRS Power Spectrum

60h-1Mpc

300h-1Mpc15h-1Mpc

• 2dFGRS power spectrum from ~250000 galaxies (Cole et al 2005)

• Results fitCDM

The 2dF QSO Redshift Survey

23340 QSOs observed

2dF QSO Power Spectrum

• Observed QSO P(k) also agrees with CDM Mock QSO Catalogue from Hubble Volume simulation

• Outram et al 2003

500h-1Mpc 50h-1Mpc

CDM Input Spectrum

Hubble Volume 1

SDSS

DR5:Million Spectra, 8000 sq degs

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

Baryon Acoustic Oscillations (BAO) as a standard ruler

• Detections of BAOs in the galaxy power spectrum at low redshift (e.g. Cole et al.,2004, Tegmark et al.,2006) and the Luminous Red Galaxy Correlation Function (Eisenstein et al., 2005) at 2-3σ

• Many large projects and studies propose to use BAOs in survey volume of ~Gpc3 as a standard ruler (DES, WFMOS, WiggleZ) to study Dark Energy Equation of State . (w= -1 for cosmological constant)

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2SLAQ LRG Wedge Plot

SDSS LRG correlation function

• Correlation function from 45000 SDSS Luminous Red Galaxies - LRGs (Eisenstein et al 2005 - see also Cole et al 2005)

• Detects Baryon Acoustic Oscillation (BAO) at s~100h-1

Mpc from z~0.35 LRGs

First Baryon Wiggles in 1985

• (s) from ~500 Durham/AAT Z Survey B<17 galaxies (Shanks et al 1985)

• First “detection” of baryon wiggles

• But not detected in Durham/UKST or 2QZ surveys

Photometric redshifts• Today - photo-z available from imaging surveys such as SDSS

• Redshift accuracy typically z~0.05 or ~150Mpc for Luminous Red Galaxies even from colour cuts

• Use photo-z to detect BAO and also Integrated Sachs Wolfe Effect

In a flat matter-dominated universe, photon blueshift and redshift on entering and leaving cluster cancels but not if DE acceleration. Results in net higher temperature near

overdensity

Physical detection of Dark Energy: Influencing the growth of structure

Integrated Sachs Wolfe (ISW)

WMAP W band

Luminous Red Galaxies (LRGs)

No ISW signal in a flat, matter dominated Universe

WMAP-SDSS cross-correlation

ISW: SDSS LRGs-WMAP• Cross-correlation of

SDSS LRGs and WMAP CMB suggests direct evidence of Dark Energy (Scranton et al 2005)

• Many caveats but various surveys now aimed at BAO and ISW using spectroscopic and photo-z LRG samples

And yet…….

Astrophysical Problems for CDM

• Too much small scale power in mass distribution?

• Mass profile of LSB galaxies less sharply peaked than predicted by CDM (Moore et al, 1999a)

• Instability of spiral disks to disruption by CDM sub-haloes (Moore et al, 1999b)

• Observed galaxy LF is much flatter than predicted by CDM - even with feedback (eg Bower et al, 2006).

• CDMMassive galaxies form late vs. “downsizing”

• Slope of galaxy correlation function is flatter than predicted by CDM mass anti-bias simple high peaks bias disallowed (eg Cole et al, 1998)

• LX-T relation galaxy clusters not scale-free?

Joe Silk’s CDM issues(~2005)

CDM Mass Function v Galaxy LF

• CDM halo mass function is steeper than faint galaxy LF

• Various forms of feedback are invoked to try and explain this issue away

• Gravitational galaxy formation theory becomes a feedback theory!

(from Benson et al 2003)

CDM haloes

CDM Mergers vs Observation

• CDM requires large amount of hierarchical merging at z<1 due to flat slope of power spectrum

• CDM E/S0 (d~10kpc) at z=0 scattered over ~1Mpc at z~1

• But latest observations show little evidence of strong dynamical evolution

No evolution seen for z<1 early-types

Brown et al (2007)

CDM predicts big galaxies form late but observe the reverse - “downsizing”!

Wake et al (2007)

QSO Luminosity Evolution

• 2dF QSO Luminosity Function (Croom et al 2003)

• Brighter QSOs at higher z

• Again not immediately suggestive of “bottom up” CDM

Fundamental Problems for CDM CDM requires 2 pieces of undiscovered physics!!!

• makes model complicated+fine-tuned • is small - after inflation, /rad ~ 1 in 10102

• Also, today ~ Matter - Why?• To start with one fine tuning (flatness) problem and end

up with several - seems circular!• anthropic principle ?!?

• CDM Particle - No Laboratory Detection• Optimists like search for neutrino!• Pessimists like search for E-M ether!

Dark Energy - bad for Astronomy?

• Simon White arguing against devoting too many resources to chasing DE

• Argues on basis of general utility of telescopes

• But not a ringing vote of confidence in DE!!!

astro-ph/0704.2291

Ed Witten -“Strings 2001”

http://theory.tifr.res.in/strings/Proceedings/witten/22.html

String theory prefers a negative (anti-de Sitter!) rather than the observed positive

Fundamental Problems for CDM CDM requires 2 pieces of undiscovered physics!!!

• makes model complicated+fine-tuned • is small - after inflation, /rad ~ 1 in 10102

• Also, today ~ Matter - Why?• To start with one fine tuning (flatness) problem and end

up with several - seems circular!• anthropic principle ?!?

• CDM Particle - No Laboratory Detection• Optimists like search for neutrino!• Pessimists like search for E-M ether!

XENON10 + CDMS2 Limits

• Best previous upper limits on mass of CDM particle from direct detection - CDMS2 in Soudan Underground lab (Akerib et al 2004)

• Now further improved by 3 months data from XENON10 experiment - (Angle et al astro-ph/0706.0039)

MSSM Neutralino Excluded?

m0, m1/2 related to masses of particles which mix to become neutralino(Ellis et al 2007 hep-ph/0706.0977)

allowed by WMAPCDMS2 direct detection upper limit

XENON10 direct detection upper limit

Fundamental Problems for CDM

• Even without , CDM model has fine tuning since CDM ~ baryon (Peebles 1985)

• Baryonic Dark Matter needed anyway!• Nucleosynthesis baryon ~ 10 x star

• Also Coma DM has significant baryon component

Coma cluster dark matter

Coma galaxy cluster gas

• Coma contains hot X-ray gas (~20%)

• X-ray map of Coma from XMM-Newton (Briel et al 2001)

• If M/L=5 then less plausible to invoke cosmological density of exotic particles than if M/L=60-600!

H0 route to a simpler model - or Shanks’ road to ruin!

• X-Ray gas becomes Missing Mass in Coma. In central r<1h-1Mpc:-

Virial Mass 61014h-1Mo

Mvir/MX =15h1.5

X-ray Gas Mass 41013h-

2.5Mo

• Thus Mvir/MX=15 if h=1.0, 5 if h=0.5, 1.9 if h=0.25

3 Advantages of low H0

Shanks (1985) - if Ho<30kms-1Mpc-1 then:

• X-ray gas becomes Dark Matter in Coma

• Inflationary baryon=1 model in better agreement with nucleosynthesis

• Light element abundances baryonh2<0.06• baryon 1 starts to be allowed if h0.3

• Inflation+EdS => =1 => Globular Cluster Ages of 13-16Gyr require Ho<40kms-1Mpc-1

• But the first acoustic peak is at l=330, not l=220

Escape routes from CDM?

• SNIa Hubble Diagram - Evolution?

• Galaxy/QSO P(k) - scale dependent bias - abandon the assumption that galaxies trace the mass!

• WMAP - cosmic foregrounds?• Galaxy Clusters - SZ inverse Compton

scattering of CMB• Galaxy Clusters - lensing of CMB

Cluster-strong lensing+shear

• HST Advanced Camera for Surveys image of A1689 at z=0.18 (Broadhurst et al 2006)

• Effects of lensing recognised to be widespread since advent of HST high resolution images 10 years ago

The 2dF QSO Redshift Survey

23340 QSOs observed

SDSS Galaxy Groups in 2QZ NGC area

2dF QSO Lensing

• Cross-correlate z~2 QSOs with foreground z~0.1 galaxy groups

• At faint QSO limit of 2dF lensinganti-correlation

• measure group masses

2dF QSO-group lensing

• Strong anti-correlation between 2dF QSOs and foreground galaxy groups

• high group masses

• M≈1 and/or mass clusters more strongly than galaxies

Myers et al 2003, 2005, Guimaraes et al, 2005, Mountrichas & Shanks 2007

Can lensing move 1st peak? • WMAP z~10

Reionisation +

• QSO lensing effects of galaxies and groups from Myers et al (2003, 2005)

• l=330 l=220

• Still need SZ for 2nd peak!?!

• other models can be fine-tuned to fit WMAP first peak?

Shanks, 2007, MNRAS, 376, 173

Conclusions

• CDM gains strong support from observational cosmology - WMAP, SNIa, P(k)

• But assumes “undiscovered physics” + very finely-tuned + problems in many other areas eg “downsizing”

• QSO lensing galaxy groups have more mass than expected from virial theorem

• Could smoothing of CMB by lensing give escape route to simpler models than CDM??

• But excitement guaranteed either via exotic dark matter+energy or by new models

Implications for CMB Lensing

• CMB lensing smoothing functions, ()/

• Only one that improves WMAP fit is ()=constant (black line)

• Requires massr-3 or steeper

• Also requires anti-bias at b~0.2 level