Observational Cosmology

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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 - PowerPoint PPT Presentation

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  • Observational Cosmology

    Tom Shanks Durham University

  • SummaryReview observational evidence for standard cosmological model - CDMThen review its outstanding problems - astrophysical + fundamental Briefly look at difficulties in finding an alternative modelConclude - 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 SpectrumSpatially flat, (k=0) universe comprising:~72% Dark Energy~24% CDM~4% Baryons(Hinshaw et al. 2003, 2006, Spergel et al. 2003, 2006)

  • Supernova CosmologySNIa 0.5mag fainter than expected at z~1 if m=1 Universe flat (k=0) + accelerating with ~0.7Vacuum/ Dark energy eqn of state Credits: ESSENCE+ Supernova Legacy Survey + HST Gold Sampledistance modulus

  • AAT 2dF Redshift Surveys 2dF ~400 fibres over 3deg2 -50 x bigger field than VLT vs 4x smaller mirror2dF galaxy and QSO z survey clustering also supports CDM

  • 2dF Galaxy Redshift Survey

  • 2dFGRS Power Spectrum2dFGRS power spectrum from ~250000 galaxies (Cole et al 2005)Results fitCDM

  • The 2dF QSO Redshift Survey23340 QSOs observed

  • 2dF QSO Power SpectrumObserved QSO P(k) also agrees with LCDM Mock QSO Catalogue from Hubble Volume simulationOutram et al 2003500h-1Mpc50h-1MpcLCDM Input SpectrumHubble Volume 1

  • SDSSDR5:Million Spectra, 8000 sq degsExtension (2005-2008): Legacy, SNe, Galaxy

  • Baryon Acoustic Oscillations (BAO) as a standard rulerDetections 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 2-3 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)

  • 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
  • Photometric redshifts

    Today - photo-z available from imaging surveys such as SDSSRedshift accuracy typically z~0.05 or ~150Mpc for Luminous Red Galaxies even from colour cutsUse 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 overdensityPhysical detection of Dark Energy: Influencing the growth of structureIntegrated Sachs Wolfe (ISW)

  • WMAP W bandLuminous Red Galaxies (LRGs)No ISW signal in a flat, matter dominated UniverseWMAP-SDSS cross-correlation

  • ISW: SDSS LRGs-WMAPCross-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. downsizingSlope 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 Silks CDM issues(~2005)

  • CDM Mass Function v Galaxy LFCDM halo mass function is steeper than faint galaxy LFVarious forms of feedback are invoked to try and explain this issue awayGravitational 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
  • No evolution seen for z
  • QSO Luminosity Evolution2dF QSO Luminosity Function (Croom et al 2003)Brighter QSOs at higher zAgain 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 10102Also, today ~ Matter - Why?To start with one fine tuning (flatness) problem and end up with several - seems circular! anthropic principle ?!?

    CDM Particle - No Laboratory DetectionOptimists 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 DEArgues on basis of general utility of telescopesBut not a ringing vote of confidence in DE!!! astro-ph/0704.2291

  • Ed Witten -Strings 2001http://theory.tifr.res.in/strings/Proceedings/witten/22.htmlString 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 10102Also, today ~ Matter - Why?To start with one fine tuning (flatness) problem and end up with several - seems circular! anthropic principle ?!?

    CDM Particle - No Laboratory DetectionOptimists 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 limitXENON10 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 baryoncomponent

  • 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

  • 3 Advantages of low H0

    Shanks (1985) - if Ho Globular Cluster Ages of 13-16Gyr require Ho

  • 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 CMBGalaxy Clusters - lensing of CMB

  • Cluster-strong lensing+shearHST 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 Survey23340 QSOs observed

  • 2dF QSO LensingCross-correlate z~2 QSOs with foreground z~0.1 galaxy groupsAt faint QSO limit of 2dF lensinganti-correlation measure group massesSDSS Galaxy Groups in 2QZ NGC area

  • 2dF QSO-group lensingStrong anti-correlation between 2dF QSOs and foreground galaxy groups high group masses M1 and/or mass clusters more strongly than galaxiesMyers 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=220Still 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 theoremCould 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 LensingCMB lensing smoothing functions, ()/Only one that improves WMAP fit is ()=constant (black line)Requires massr-3 or steeperAlso requires anti-bias at b~0.2 level