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Observational Cosmology

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

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Observational Cosmology

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  1. Observational Cosmology Tom Shanks Durham University

  2. 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!

  3. 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)

  4. WMAP 3-Year CMB Map

  5. 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)

  6. Supernova Cosmology • 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 distance modulus Credits: ESSENCE+ Supernova Legacy Survey + HST Gold Sample

  7. 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

  8. 2dF Galaxy Redshift Survey

  9. 300h-1Mpc 15h-1Mpc 60h-1Mpc 2dFGRS Power Spectrum • 2dFGRS power spectrum from ~250000 galaxies (Cole et al 2005) • Results fitCDM

  10. The 2dF QSO Redshift Survey 23340 QSOs observed

  11. 2dF QSO Power Spectrum • Observed QSO P(k) also agrees with LCDM Mock QSO Catalogue from Hubble Volume simulation • Outram et al 2003 LCDM Input Spectrum Hubble Volume 1 500h-1Mpc 50h-1Mpc

  12. SDSS DR5:Million Spectra, 8000 sq degs Extension (2005-2008): Legacy, SNe, Galaxy

  13. 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 ~Gpc3as a standard ruler (DES, WFMOS, WiggleZ) to study Dark Energy Equation of State . (w= -1 for cosmological constant)

  14. 2SLAQ LRG Wedge Plot

  15. 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

  16. 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

  17. 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

  18. Integrated Sachs Wolfe (ISW) Physical detection of Dark Energy: Influencing the growth of structure 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

  19. WMAP-SDSS cross-correlation WMAP W band Luminous Red Galaxies (LRGs) No ISW signal in a flat, matter dominated Universe

  20. 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

  21. And yet…….

  22. 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). • CDMMassive 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?

  23. Joe Silk’s CDM issues(~2005)

  24. 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! CDM haloes (from Benson et al 2003)

  25. 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

  26. Wake et al (2007) Brown et al (2007) No evolution seen for z<1 early-types CDM predicts big galaxies form late but observe the reverse - “downsizing”!

  27. QSO Luminosity Evolution • 2dF QSO Luminosity Function (Croom et al 2003) • Brighter QSOs at higher z • Again not immediately suggestive of “bottom up” CDM

  28. 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!

  29. 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

  30. Ed Witten -“Strings 2001” String theory prefers a negative  (anti-de Sitter!) rather than the observed positive  http://theory.tifr.res.in/strings/Proceedings/witten/22.html

  31. 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!

  32. 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)

  33. MSSM Neutralino Excluded? allowed by WMAP CDMS2 direct detection upper limit XENON10 direct detection upper limit m0, m1/2 related to masses of particles which mix to become neutralino (Ellis et al 2007 hep-ph/0706.0977)

  34. 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

  35. Coma cluster dark matter

  36. 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!

  37. H0 route to a simpler model - or Shanks’ road to ruin! • X-Ray gas becomes Missing Mass in Coma. In central r<1h-1Mpc:- • Thus Mvir/MX=15 if h=1.0, 5 if h=0.5, 1.9 if h=0.25

  38. 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 h0.3 • 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

  39. 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

  40. 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

  41. The 2dF QSO Redshift Survey 23340 QSOs observed

  42. 2dF QSO Lensing • Cross-correlate z~2 QSOs with foreground z~0.1 galaxy groups • At faint QSO limit of 2dF lensinganti-correlation •  measure group masses SDSS Galaxy Groups in 2QZ NGC area

  43. 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

  44. 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

  45. 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

  46. Implications for CMB Lensing • CMB lensing smoothing functions, ()/ • Only one that improves WMAP fit is ()=constant (black line) • Requires massr-3 or steeper • Also requires anti-bias at b~0.2 level

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