Observational Cosmology

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Observational Cosmology

• Tom Shanks
• Durham University

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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!

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Observational cosmology supports ?CDM!

• Boomerang WMAP CMB experiments detect acoustic
  peak at l220(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)

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(No Transcript)
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WMAP 3-Year CMB Map
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WMAP 3-Year Power Spectrum
Spatially flat, (k0) universe comprising 72
Dark Energy 24 CDM 4 Baryons (Hinshaw et al.
2003, 2006, Spergel et al. 2003, 2006)
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Supernova Cosmology

• SNIa 0.5mag fainter than expected at z1 if ?m1
• ? Universe flat (k0) accelerating with ??0.7
• Vacuum/ Dark energy eqn of state

distance modulus
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

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2dF Galaxy Redshift Survey
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2dFGRS Power Spectrum

• 2dFGRS power spectrum from 250000 galaxies
  (Cole et al 2005)
• Results fit?CDM

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The 2dF QSO Redshift Survey
23340 QSOs observed
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2dF QSO Power Spectrum
LCDM Input Spectrum

• Observed QSO P(k) also agrees with LCDM Mock QSO
  Catalogue from Hubble Volume simulation
• Outram et al 2003

Hubble Volume ?1?
500h-1Mpc
50h-1Mpc
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SDSS
DR5Million Spectra, 8000 sq degs Extension
(2005-2008) Legacy, SNe, Galaxy
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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
  2-3s
• 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
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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
  s100h-1 Mpc from z0.35 LRGs

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First Baryon Wiggles in 1985

• ?(s) from 500 Durham/AAT Z Survey Blt17 galaxies
  (Shanks et al 1985)
• First detection of baryon wiggles
• But not detected in Durham/UKST or 2QZ surveys

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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

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

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And yet.
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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?

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Joe Silks ?CDM issues(2005)
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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)
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CDM Mergers vs Observation

• ?CDM requires large amount of hierarchical
  merging at zlt1 due to flat slope of power
  spectrum
• ?CDM ? E/S0 (d10kpc) at z0 scattered over
  1Mpc at z1
• But latest observations show little evidence of
  strong dynamical evolution

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No evolution seen for zlt1 early-types
?CDM predicts big galaxies form late but observe
the reverse - downsizing!
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QSO Luminosity Evolution

• 2dF QSO Luminosity Function (Croom et al 2003)
• Brighter QSOs at higher z
• Again not immediately suggestive of bottom up
  ?CDM

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Fundamental Problems for ?CDM

• ?CDM requires 2 pieces of undiscovered physics!!!
• ??makes model complicatedfine-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!

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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
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Ed Witten -Strings 2001
String theory prefers a negative ? (anti-de
Sitter!) rather than the observed positive ?
http//theory.tifr.res.in/strings/Proceedings/witt
en/22.html
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Fundamental Problems for ?CDM

• ?CDM requires 2 pieces of undiscovered physics!!!
• ??makes model complicatedfine-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!

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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)

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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)
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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

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Coma cluster dark matter
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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/L5 then less plausible to invoke
  cosmological density of exotic particles than if
  M/L60-600!

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

• X-Ray gas becomes Missing Mass in Coma. In
  central rlt1h-1Mpc-

Virial Mass ? 6?1014h-1Mo
Mvir/MX 15h1.5
X-ray Gas Mass ??4?1013h-2.5Mo

• Thus Mvir/MX15 if h1.0, 5 if h0.5, 1.9 if
  h0.25

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3 Advantages of low H0

• Shanks (1985) - if Holt30kms-1Mpc-1 then
• X-ray gas becomes Dark Matter in Coma
• Inflationary ?baryon1 model in better agreement
  with nucleosynthesis
• Light element abundances ? ?baryonh2lt0.06
• ???baryon ?1 starts to be allowed if h?0.3
• InflationEdS gt ??1 gt Globular Cluster Ages of
  13-16Gyr require Holt40kms-1Mpc-1
• But the first acoustic peak is at l330, not l220

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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

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Cluster-strong lensingshear

• HST Advanced Camera for Surveys image of A1689 at
  z0.18 (Broadhurst et al 2006)
• Effects of lensing recognised to be widespread
  since advent of HST high resolution images 10
  years ago

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The 2dF QSO Redshift Survey
23340 QSOs observed
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2dF QSO Lensing

• Cross-correlate z2 QSOs with foreground z0.1
  galaxy groups
• At faint QSO limit of 2dF lensing?anti-correlation
  
• ? measure group masses

SDSS Galaxy Groups in 2QZ NGC area
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2dF QSO-group lensing

• Strong anti-correlation between 2dF QSOs and
  foreground galaxy groups
• ?high group masses
• ? ?M1 and/or mass clusters more strongly than
  galaxies

Myers et al 2003, 2005, Guimaraes et al, 2005,
Mountrichas Shanks 2007
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Can lensing move 1st peak?

• WMAP z10 Reionisation
• QSO lensing effects of galaxies and groups from
  Myers et al (2003, 2005)
• ? l330 ? l220
• Still need SZ for 2nd peak!?!
• ? other models can be fine-tuned to fit WMAP
  first peak?

Shanks, 2007, MNRAS, 376, 173
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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
  matterenergy or by new models

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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 b0.2 level