physcol

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I gave this at badhoneff in Sept/09. This was a
90 minutes lecture. I finished on time but was
rushed at the end
For Barcelona, I commented out slides on evidence
for DM and on the CMB. Here I have 2 60 min
lectures
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The formation of cosmic structure
Carlos S. Frenk Institute for Computational
Cosmology, Durham
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Flammarion 1888 tete des etoiles
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The emergence of a cosmological paradigm
? LCDM model

• The CDM model
• What is it?
• How do we test it?

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The LCDM model
A cosmological model is a model for the dynamics
of the Universe and for the origin and evolution
of cosmic structure.

• It must specify
• The material content of the universe
• The initial conditions for the formation of
  structure
• The growth mechanism
• The values of the fundamental cosmological
  parameters

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The content of our universe
Dark matter ? matter that does not emit light at
any wavelength
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What is the universe made of?
r rrel rmass rvac
? 1 for a flat univ.
critical density density that makes univ. flat

• Radiation (CMB, T2.7260.005 oK) ?r
  4.7 x 10-5

• Neutrinos
  ?n 6 x 10-2 (ltmngt/ev)

• Baryons
  ?b 0.044 0.004

• Dark matter (cold dark matter) ?dm
  0.20 0.04

• Dark energy (cosm. const. L) ??
  0.75 0.04

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Evidence for dark matter
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Galaxy rotation curves
Flat Vc ? M(ltr) ? r but
L(ltr)const ? dark halos around
galaxy
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Mapping the dark matter
Light rays are deflected by gravity (Emc2)
Distant galaxy
Observer
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Gravitational lensing
Light from distant galaxies is deflected by dark
matter in cluster, distorting the galaxies
images into arcs
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The nature of the dark matter
? Dark matter must be non-baryonic
13
Non-baryonic dark matter candidates
Type candidate mass
hot neutrino a few eV
warm Sterile neutrino keV-MeV
cold axion neutralino 10-5eV-gt100 GeV
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? ?? ?b ?dm ?? 1
In LCDM
The simplest cosmological model would have a flat
geometry and no dark energy, ie Wm1 and WL0
Clusters give direct evidence for Wm lt 1
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X-ray emission from hot plasma in clusters
Galaxy clusters
Images from David Buote
About 90 of baryons in clusters are in hot gas
X-rays ? gas mass Photometry ? stellar mass Gas
is in hydrostatic equilibrium so X-rays/lensing
? total gravitating mass
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W from the baryon fraction in clusters
The baryon fraction in clusters, fb, is related
to the universal baryon fraction by
White, Navarro, Evrard Frenk 93
where g1 if fb has the universal value
simulations ? g 0.9 10
X-rayslensing ? fb (0.060h-3/2 0.009)
10 BBNS, CMB ? Wbh2 0.019 20 HST
? h 0.7 10
Allen etal 04
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W lt 1 open or flat universe?
White et al 1993
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(Some) evidence for dark energy
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Evidence for ? from high-z supernovae
WL
Wm
SN type Ia (standard candles) at z0.5 are
fainter than expected even if the Universe were
empty
? The cosmic expansion must have been
accelerating since the light was emitted
Perlmutter et al 98
a/a01/(1z)
Reiss et al 98
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Friedmann equations

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Evidence for ? from high-z supernovae
Distant SN are fainter than expected if expansion
were decelerating
Riess et al 98
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Evidence for ? from high-z supernovae

• Latest data rules out WL 0.
• Main concerns
• Physics of SNIa not understood
• Systematic errors?

Clocchiatti et al 06
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The LCDM model

• A cosmological model must specify
• The material content of the universe
• The initial conditions for the formation of
  structure
• The growth mechanism
• The values of the fundamental cosmological
  parameters

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The beginning of the Universe
In 1980, a revolutionary idea was proposed
our universe started off in an unstable state
(vacuum energy) and as a result expanded very
fast in a short period of time ? cosmic inflation
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Cosmic Inflation

• Inflation theory predicts
• Flat geometry (??1)
• (eternal expansion)
• Small ripples in mass distribution

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Spectrum of inhomogeneities
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In practice, the correlation function is
estimated as
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The origin of cosmic structure
n1
? FLAT UNIVERSE
hot neutrino a few eV
warm Sterile neutrino keV-MeV
cold axion neutralino 10-5eV-gt100 GeV
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The LCDM model

• A cosmological model must specify
• The material content of the universe
• The initial conditions for the formation of
  structure
• The growth mechanism
• The values of the fundamental cosmological
  parameters

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Linear theory fluctuation growth rate
The growth rate of density fluctuations depends
on Wm , WL and w
Wm 0.25, WL 0.75, w-1
Growth factor
Wm 1, WL 0
(At high-z, the growth rate always approaches the
Wm 1 case)
z
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The cosmological model
Growth mechanism
Gravitational instability driven by dark matter
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Dynamics of structure formation
Gravitygeneral relativity, butNewtonian
approximation in expanding space usually
sufficient
N-body simulations
dark matter is collisionless (described by Vlasov
equation)
Monte-Carlo integration as an N-body system
3N coupled, non-linear differential equations of
second order
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The Tree-PM method (Gadget-2)
Periodic peculiar potential
Idea Compute the long-range force with the PM
algorithm, and only a local short-range force
with the tree.
Let's split the potential in Fourier space into a
long-range and a short-range part
Solve in real space with TREE

• Solve with PM-method
• CIC mass assignment
• FFT
• multiply with kernel
• FFT backwards
• Compute force with 4-point finite difference
  operator
• Interpolate forces to particle positions

FFT gives long-range force in simulation box
Tree has to be walked only locally
5 rs
short-range force-law
Volker Springel

• Accurate and fast long-range force
• No force anisotropy
• Speed is insensitive to clustering (as for tree
  algorithm)
• No Ewald correction necessary for periodic
  boundary conditions

Advantages of this algorithm include
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dalla Vechia, Jenkins Frenk
Comoving coordinates
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The LCDM model

• A cosmological model must specify
• The material content of the universe
• The initial conditions for the formation of
  structure
• The growth mechanism
• The values of the fundamental cosmological
  parameters

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The cosmological model
Cosmological parameters (simplest case)
Neutrino mass fraction
tensor index
Wbh2
curvature
dark energy
tensor/scalar
scalar index
Hubble parameter
Wdmh2
fluctn amplitude
pwr
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Hot vs cold dark matter?
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The origin of cosmic structure

• Hot DM (eg ev neutrino)
• Top-down formation
• Cold DM (eg neutralino)
• Bottom-up (hierachical)

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Neutrino (hot) dark matter
Free-streaming length so large that superclusters
form first and galaxies are too young
Neutrinos cannot make an appreciable contribution
to W and mnltlt 30 ev
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Non-baryonic dark matter cosmologies
Neutrino dark matter produces unrealistic
clustering
Early CDM N-body simulations gave
promising results
Neutrinos W1
HDM W1
In CDM structure forms hierarchically
Davis, Efstathiou, Frenk White 85
Davis, Efstathiou, Frenk White 85
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The paradigm of structure formation LCDM
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The cold dark matter cosmogony
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The cold dark matter cosmogony
The CDM model is an intrinsically implausible
model, all the more so when the cosmological
constant L is required.
?? Observational tests are crucial
CDM model is well specified ?? testable
predictions possible
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The cold dark matter cosmogony
Observational tests

• Cosmic microwave background fluctuations
• Galaxy distribution
• Structure of dark matter halos

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The microwave background radiation
Plasma
t0
t380 000 yrs
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The microwave background radiation
inflation
380 000 years after the big Bang
Plasma
T2.73 K
z ?
z 1000
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The CMB
1992
The cosmic microwave background radiation (CMB)
provides a window to the universe at t3x105
yrs In 1992 COBE discovered temperature
fluctuations (DT/T10-5) consistent with
inflation predictions
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The CMB
1992
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The CMB
1992
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The CMB
1992
2003
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WMAP temp anisotropies in CMB
Amplitude of fluctuations
3-year data
The amplitude of the CMB ripples is exactly as
predicted by inflationary cold dark matter
theory The position of the first peak
consistent ? FLAT UNIVERSE
Hinshaw etal 06
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The Emergence of the Cosmic Initial
Conditions
3-year data
Polarization TE x-power spectrum
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The cold dark matter cosmogony
Observational tests

• Cosmic microwave background fluctuations
• Galaxy distribution
• Structure of dark matter halos

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The 2dF Galaxy Redshift Survey
221,000 redshifts
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Sloan Digital Sky Survey
500,000 galaxy redshifts
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The cold dark matter cosmogony
Observational tests

• Cosmic microwave background fluctuations
• Galaxy distribution
• Structure of dark matter halos

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Testing the CDM paradigm
z1000
dr/r 10-5
Initial conditions LCDM
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Testing the CDM paradigm
Small scales
Initial conditions LCDM
z0
dr/r 1-106
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Moore's Law for Cosmological N-body Simulations

• Computers double their speed every 18 months
• A naive N-body force calculation needs N2 op's
• Simulations double their size every 16.5 months
• N 1010 should have been reached in 2008
• ..but was reached in 2004

Springel et al 2005
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The Millennium simulation

• Cosmological N-body simulation
• 10 billion particles
• 500 h-1 Mpc box
• mp 8?108 h-1 Mo
• W 1 Wm0.25 W b0.045 h0.73 n1 s8
  0.9
• 20 ?106 gals brighter than LMC

UK, Germany, Canada, US collaboration
Simulation data available at http//www.mpa-garc
hing.mpg.de/Virgo
Carried out at Garching using L-Gadget by V.
Springel
Pictures and movies available at
www.durham.ac.uk/virgo
(27 Tbytes of data)
Nature, June/05
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The mass power spectrum
z0
The non-linear mass power spectrum is accurately
determined by the Millennium simulation over
large range of scales
z1
z3.05
z7
dk2
z14.9
linear theory
k h/Mpc
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Solid curves are the empirical fitting formula
from Jenkins et al 2001 with no parameters
adjusted At z 0 half of all mass is in lumps
of M gt 2.1010MO
M2/r dn/dM
Jenkins etal 01
Mass (h-1 Mo)
Springel et al 2005
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z 0 Dark Matter
What is the connection between the distributions
of galaxies and dark matter?
Springel etal 05
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z 0 Dark Matter
Springel etal 04
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z 0 Galaxy light
Croton etal 05
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real
simulated
Springel, Frenk White Nature, April 06
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Real and simulated 2dF galaxy survey
? Real Simulated ?
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Galaxy autocorrelation function

• The galaxy 2-point correlation function in the
  MS agrees well with 2dFGRS
• Galaxies are less clustered than DM on small
  scales

Springel et al 2005
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Clustering on very large scales
x(r) can be measured accurately to r30 h-1Mpc
(k0.2/ h-1Mpc) in 2dFGRS or SDSS
On larger scales, it is better to calculate the
power spectrum (k)
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The final 2dFGRS power spectrum
2dFGRS P(k) well fit by LCDM model convolved with
window function
Cole, Percival, Peacock, Baugh, Frenk 2dFGRS 05
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The final 2dFGRS power spectrum
P(k) / Pref(Wbaryon0)
LCDM model
LCDM convolved with window
Cole 2dFGRS 05
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CMB anistropies and large-scale structure
Meiksin etal 99
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Baryon wiggles in the galaxy distribution
Power spectrum from MS divided by a baryon-free
LCDM spectrum Galaxy samples matched to
plausible large observational surveys at given z
z3
z7
DM
gals
z0
z1
Springel et al 2004
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The final 2dFGRS power spectrum
P(k) / Pref(Wbaryon0)
Baryon oscillations conclusively detected in
2dFGRS!!! Demonstrates that structure grew by
gravitational instability in LCDM universe
LCDM model
LCDM convolved with window
Also detected in SDSS LRG sample (Eisenstein etal
05)
Cole 2dFGRS 05
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SDSS LRG correlation function
Again, CDM models fit the correlation function
adequately well (although peak height is slightly
too large assuming ns1, h0.72) Wbh2 0.024,
Wmh2 0.1330.011, ? Wb/Wm 0.18
x(s)
Eisenstein et al. 05
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Cosmological parameters CMB 2dF
The 2dF power spectrum depends on Wmh, Wb /Wm,
s8gal, fn,
The CMB power spectrum depends on
Combining 2dF and CMB breaks parameter
degeneracies
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Parameter constraints
CMB only
Sanchez etal 05
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Effect of neutrinos
Free-stream length 80(S mn /eV)-1 Mpc
(Wm h2 Smn / 93.5 eV) Smn 1 eV causes lower
power at almost all scales, or a bump at the
largest scales
2dFGRS ? Smn lt 1.2 ev
Sanchez et al 05
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Parameter estimation
CMB 2dFGRS
Wm 0.224 ? 0.024 Wb 0.055 ?
0.007 Wk -0.031 ? 0.018 WL
0.809 ? 0.037 h 0.683 ? 0.031 ns
1.07 ? 0.10 s8 0.812 ? 0.072

• Data
• CMB ? WMAP, CBI, ACBAR and VSA
• LSS ? 2dFGRS
• Free parameters
• Wk , WL , Wcdmh2, Wbh2, ns, t, As

Sanchez etal 06
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Parameter estimation
CMB 2dFGRS
WMAP 1-year
Sanchez etal 05
Wm 0.237 ? 0.020 Wb 0.042 ? 0.003
WL 0.763 ? 0.020 h 0.735 ?
0.022 t 0.118 ? 0.056 ns
0.954 ? 0.023 s8 0.773 ? 0.050
Wm 0.236 ? 0.023 Wb 0.042 ? 0.003
WL 0.764 ? 0.023 h 0.732 ?
0.021 t 0.083 ? 0.029 ns
0.948 ? 0.016 s8 0.737 ? 0.039
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Parameter estimation
CMB 2dFGRS
These values agree with constraints from
Wtot 1
WMAP 3-years
Wm 0.236 ? 0.023 Wb 0.042 ? 0.003
WL 0.764 ? 0.023 h 0.732 ?
0.021 t 0.083 ? 0.029 ns
0.948 ? 0.016 s8 0.737 ? 0.039

• Big Bang nucleosynthesis
• HST determination of Ho
• Cluster abundance
• Gravitational lensing (2s)
• Ly-a forest (2s)

Spergel etal 06
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Constraints on w from SnIa, WMAP and 2dFGRS
Assume wconst (cosmological constant)
w-0.9 ? 0.1
Spergel et al 2006
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The cosmic power spectrum from the CMB to the
2dFGRS
CMB

• Convert angular separation to distance (and k)
  assuming flat geometry
• Extrapolate to z0 using linear theory

z0
WMAP
2dFGRS
? LCDM provides an excellent description of mass
power spectrum from 10-1000 Mpc
Sanchez et al 06
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The cold dark matter cosmogony
Observational tests

• Cosmic microwave background fluctuations
• Galaxy distribution
• Structure of dark matter halos

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A cold dark matter universe

• There are two famous problems on small scales
• The halo core problem
• The satellite problem

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Explanations for the core/satellite "crises"

• The dark matter is warm
• The dark matter has a finite self-scattering
  cross-section
• The primordial density power spectrum has a
  break (or running spectral index)
• There is no dark matter -- gravity needs
  modifying
• Astrophysics baryon effects, black holes, bars
• The comparison of models and data is incorrect

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The structure of cold dark matter halos
The halo cusp problem
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z 0.0
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The Density Profile of Cold Dark Matter Halos
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The Aquarius programme
Carlos Frenk Amina Helmi Adrian Jenkins Aaron
Ludlow Julio Navarro Volker Springel, Mark
Vogelsberger Jie Wang Simon White Aquarius
Shaun Cole Andrew Cooper Gabriella de
Lucia Takashi Okamoto
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The Aquarius programme

• 6 different galaxy size halos simulated at
  varying resolution, allowing for a proper
  assessment of numerical convergence and cosmic
  variance

Simulation data, movies, pictures available
at www.mpa-garching.mpg.de/Virgo www.durham.ac.uk
/virgo
Springel et al 08
UK, Germany, Canada, Japan, US collaboration
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Aquarius - the movie
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Images of all Aquarius halos (level-2)
The Aquarius Billennium halo simulation. A dark
matter halo with 1 billion particles within the
virial radius.
500 kpc
Play Movie
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Density profile r(r)
z0
Orignal NFW simulations resolved down to 5 of
rvir
NFW
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Density profile r(r)
z0
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Density profile r(r) convergence test
z0
The spherically averaged density profiles show
very good convergence, and are approximately fit
by a NFW profile
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Deviations from NFW
The density profile is fit by the NFW form to
10-20. In detail, the shape of the
profile is slightly different.
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Universality of the mass profile
6 HALOS LEVEL 2 RESOLUTION
density ? r2
circular velocity
scaled radius
Slight but significant deviations from
similarity. A third parameter needed to
describe accurately mass profiles of CDM halos.
Einasto
Virgo Consortium 08
102
The structure of the cusp
slope
slope
Moore etal
Moore etal
NFW
NFW
Einasto
Einasto
radius
scaled radius
Logarithmic slope scales like a power-law of
radius the Einasto profile Innermost profile
shallower than r-1
Virgo Consortium 08
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A Cold dark matter universe
N-body simulations show that cold dark matter
halos (from galaxies to clusters) have
Cuspy density profiles
Does nature have them?
Look in galaxies and clusters
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A cold dark matter universe
Probing the structure of cluster halos with X-rays
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A2589 another relaxed cluster
(Buote Lewis 2004)
NFW
Mass within R
R (kpc)
(z0.0414 1 arcsec 0.83 kpc)
NFW (c4.9 2.4) is good fit for rgt0.02 Rvir
15 ks Chandra data show no asymmetries from 1 kpc
to 1 Mpc
From David Buote
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The central density profile of galaxy cluster
dark halos
X-ray data
Mass profile of galaxy clusters, from X-ray data
assumption of hydrostatic equilibrium
NFW
Excellent agreement with CDM halo predictions
Pointecouteau et al 05
107
The central density profile of galaxy cluster
dark halos
X-ray data
Mass profile of galaxy clusters, from X-ray data
assumption of hydrostatic equilibrium
Excellent agreement with CDM halo predictions
108
A cold dark matter universe
Probing the structure of cluster halos using
gravitational lensing
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The density profile of galaxy cluster dark halos
Johnston et al 07
Total
NFW
BCG
Weak lensing for 130,000 groups and clusters from
SDSS
Projected surface density
Model contributions from brightest central
galaxy, cluster dark halo and neigbouring dark
halos
r h-1Mpc
r h-1Mpc
r h-1Mpc
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The density profile of galaxy cluster dark halos
Concentration-mass relation
Weak lensing for 130,000 groups and clusters from
SDSS
CDM prediction
(Neto et al 07)
Johnston et al 07
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Halo structure conclusions

• Halos extend to 10 times the 'visible' radius
  of galaxies and contain 10 times the mass in the
  visible regions
• Halos are triaxial ellipsoids (not spherical)
• Halos have nearly universal cuspy" density
  profiles
• Cusps are inferred in cluster halos

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The satellite problem
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The satellites of the Local Group
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Halo substructures
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The Aquarius programme

• 6 different galaxy size halos simulated at
  varying resolution, allowing for a proper
  assessment of numerical convergence and cosmic
  variance

Springel et al 08
116
z 1.5
N200750?106
24003 run
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N(M) ? Ma
a -1.90
Msub Mo
300,000 subhalos within virialized region in
Aq-A-1
Springel, Wang, Vogelsberger, Ludlow, Jenkins,
Helmi, Navarro, Frenk White 08
118
N(M) ? Ma
a -1.90
Msub Mo
MASS PER LOG INTERVAL
Msub2 dN/dMsub h-1 Mo
Msub Mo
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The substructure circ velocity function
We find 3 times as many subhalos as Diemand et al
find for VL I, but VLII is close to our ensemble
120
z 0.1
24003 run
How many of these subhalos actually make a
visible galaxy?
and what do they look like ?
121
Feedback in galaxy formation
The faint end of luminosity function White
Rees 78 ? Injection of supernovae/stellar wind
energy
122
Photoionization
123
Luminosity Function of Local Group Satellites

• Photoionization inhibits the formation of
  satellites
• Abundance of satellies reduced by large factor!

LCDM
Benson, Frenk, Lacey, Baugh Cole 02 (see also
Kauffman etal 93, Bullock etal 01)
124
The satellites of the Local Group
Satellite LF
LF of satellites within the virial radii of MW
and M31
Model
data
Photoionization inhibits the formation of
satellites
Benson, Frenk, Lacey, Baugh Cole 02 (see also
Kauffman etal 93, Bullock etal 01)
125
The satellites of the Milky Way
Name Year discovered
LMC 1519
SMC 1519
Sculptor 1937
Fornax 1938
Leo II 1950
Leo I 1950
Ursa Minor 1954
Draco 1954
Carina 1977
Sextans 1990
Sagittarious 1994
126
The satellites of the Milky Way
Several new satellites discovered in the past few
years
Name Year discovered
Canis Major 2003
Ursa Major I 2005
Wilman I 2005
Ursa Major II 2006
Bootes 2006
Canes Venatici I 2006
Canes Venatici II 2006
Coma 2006
Leo IV 2006
Hercules 2006
Leo T 2007
Segue I 2007
Boo II 2007
Segue II 2009
Name Year discovered
LMC 1519
SMC 1519
Sculptor 1937
Fornax 1938
Leo II 1950
Leo I 1950
Ursa Minor 1954
Draco 1954
Carina 1977
Sextans 1990
Sagittarious 1994
127
Luminosity Function of Local Group Satellites

• Photoionization inhibits the formation of
  satellites
• Abundance of satellies reduced by large factor!

LCDM
Benson, Frenk, Lacey, Baugh Cole 02 (see also
Kauffman etal 93, Bullock etal 01)
128
Modelling baryonic physics in Aquarius halos
The Aquarius Billennium halo simulation. A dark
matter halo with 1 billion particles within the
virial radius.
500 kpc
Play Movie
129
Luminosity function of Milky Way satellites
Semi-analytic modelling
Aquarius halos
Reionization as in the Okamoto et al simulations
data
Cooper, Cole, Frenk et al 09
130
The cold dark matter model
Detecting cold dark matter
131
Cold dark matter searches
- Indirect detection -
Supersymmetric particles annihilate and lead to
production of g-rays which may be observable by
GLAST/FERMI
? Theoretical expectation requires knowing r(x)
Often assume SHM boost factor to account
for substructure
132
How lumpy is the halo?
133
z 0.1
A galactic dark matter halo
1.1 billion particles inside rvir
Springel, Wang, Volgensberger, Ludlow, Jenkins,
Helmi, Navarro, Frenk White 08
24003 run
134
The subhalo number density profile
n(r)/ltngt

• The spatial distribution of subhalos (except
  for the few most massive ones) is independent of
  mass
• Most subhalos are at large radii -- subhalos
  are more effectively destroyed near the centre
• Most subhalos have completed only a few orbits
  dynamical friction unimportant below a subhalo
  mass threshold
• Subhalos are far from the Sun

r kpc
dfn(ltr)/dlog r
Enclosed no. fraction of substructures of
different mass
Sun
r kpc
135
The cold dark matter power spectrum
The linear power spectrum (power per octave )
Assumes a 100GeV wimp Green et al 04
k3P(k)
k h Mpc-1
136
Direct cold dark matter searches
How smooth is the dark matter mass distribution
at the solar position?
137
How lumpy is the MW halo?
Mass fraction in subhalos as a fn of cutoff mass
in CDM PS
The Milky Way halo is expected to be quite smooth!
Mass fraction in subhalos within Rsun lt 0.1
138
Mass and annihilation radiation profiles of a MW
halo
gt 105 M?
gt 108 M?
main halo Lum
main halo Mass
subhalos (smooth) Lum
139
The Milky Way seen in annihilation radiation
140
The Milky Way seen in annihilation radiation
141
The Milky Way seen in annihilation radiation
142
The Milky Way seen in annihilation radiation
143
The Milky Way seen in annihilation radiation
Aquarius simulation N200 1.1 x 109
Springel et al 08
144
A blueprint for detecting halo CDM
S/NF/(?2h??psf)1/2
S/N for detecting subhalos in units of that for
detecting the main halo. 30 highest
S/N objects, assuming use of optimal filters
(S/N)/(S/N)main halo

• Highest S/N subhalos have 1 of S/N of main halo
• Highest S/N subhalos have 10 times S/N of known
  satellites
• Substructure of subhalos has no influence on
  detectability

145
The Milky Way seen in annihilation radiation
146
The first all-sky image from GLAST/Fermi
147
The origin of cosmic structure
148
Conclusions the LCDM model

• LCDM is an intrinsically implausible model that
  requires

• An early epoch of inflation
• Quantum fluctuations in the early universe
• Non-baryonic dark matter
• Dark energy

• Yet, it agrees with staggering amount of data,
  from CMB to gals
• Existence of dark energy supported by WMAP2dFGRS
  
• Most cosmological params determined by
  WMAP2dFGRS Current limits wlt-0.9 (p wrc2)

149
Conclusions LCDM on small scales
Halos have cuspy profiles, with inner slope
shallower than -1 Profiles of relaxed halos
described by NFW or Einasto form
X-rays/lensing ? Evidence for cusps in relaxed
cluster halos
150
Open questions
Dark matter

• What is it?
• If SUSY particle, will LHC make it?
• Will direct searches find it?
• Is LCDM really right on large scales?
• Map DM directly ? gravitational lensing
• Measure PS growth ? galaxy surveys at high z
• Do galaxies trace mass ? ? galaxy formation
  theory
• Is LCDM right on small scales?
• Detect dark substructures ? gravitational
  lensing
• Sort out rotation curve mess ? simulations,
  observations
• Better study of cluster halo structure ?
  X-rays, lensing

151
Open questions
Dark energy

• What is it?
• Nothing is known! ? theory
• Is it
• constant in time (L) or varying (quintessence)?

• Fluctuation growth rate and geometry depend on
  w(z)
• effects are small but measurable
• baryon wiggles in clusters are a promising
  diagnostic

152
Our implausible Universe
153
The golden era in cosmology is not over
It has probably just begun!
154
Inelastic scattering
2008 Xmas card from the Finkbeiners