Testing LCDM on Large and Small Scales Carlos S. Frenk Institute For

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University of Durham

Testing LCDM on large and small scales

Carlos S. Frenk Institute for Computational Cosmology, Durham

Institute for Computational Cosmology University of Durham The emergence of a cosmological paradigm

⇒ ΛCDM model

cosmological constant cold dark matter or dark energy

The CDM model:

• What is it?

• How do we test it?

Institute for Computational Cosmology The ΛCDM model

• Material content: Cold dark matter (eg neutralino;21%), baryons (4%), dark energy (Λ; 75%)

• Initial conditions for formation of structure: Quantum fluctuations during inflation: 2 n |δk| k , n≈1; Gaussian amplitudes

• Growth processes: Gravitational instability

Ω size = 0.21, Ω = 0.04, Ω = 0.75, • Parameters: CDM b Λ h = 0.70,σ 8 = 0.9, ...

time € The density & geometry of the University of Durham Universe

density Ω= ρ = ρrel + ρmass + ρvac critical density

critical density = density that makes univ. flat:

In ΛCDM: Ωtot= Ω matter+ Ω Λ + Ω radn = 1 consistent with the flat universe expected in inflation

Institute for Computational Cosmology University of Durham The cold dark matter cosmogony

The CDM model is an intrinsically implausible model, all the more so when the cosmological constant Λ is required.

Couldn’t we have something simpler?

Institute for Computational Cosmology University of Durham

In particular, couldn’t we just have

Ωmatter = 1

Clusters give direct

evidence for Ωmatter < 1

Institute for Computational Cosmology Galaxy University of Durham X-ray emissionclusters from hot plasma in clusters Images from David Buote

(z=0.0348 1' A2052 Perseus (z=0.0183 ) ) Hydra A (z=0.054) About 90% of baryons in clusters are in hot gas X-rays ⇒ gas mass Photometry ⇒ stellar mass ⇒ Baryon fraction, f Gas in hydrostatic equilibrium so X-rays b (or lensing) total gravitating mass ⇒ Institute for Computational Cosmology Ω from the baryon fraction in clusters University of Durham

In clusters matter that has fallen in

is still in the cluster (rvir ~ rnon-linear) size ⇒ baryon fraction in clusters ≈ baryon fraction of universe

time

Mb = Mgas + Mstars

White, Navarro, Evrard & Frenk ‘93 where γ=1 if fb has the universal value Simulations =0.9 ⇒ γ Institute for Computational Cosmology Ω from the baryon fraction in clusters University of Durham

The baryon fraction in clusters, fb, is related to the universal baryon fraction by: Mb Ωb White, Navarro, fb = = γ Evrard & Frenk ‘93 Mtot Ωm where γ=1 if fb has the universal value simulations  γ = 0.9 + 10% X-rays+lensing  f = (0.060h-3/2 +0.009) +10% € b 2 + BBNS, CMB  Ωbh = 0.019 20% HST  h = 0.7 + 10%

Ωbγ Ωm = = 0.31± 0.12 Allen etal ‘04 f b Institute for Computational Cosmology

€ University of Durham Ω < 1: open or flat universe?

Open universe

Ωmatter < 1 ⇒ Cosmological constant to give Ωtot=1

White et al 1993

Institute for Computational Cosmology University of Durham

(Some) evidence for dark energy

Institute for Computational Cosmology Evidence for Λ from high-z University of Durham supernovae

Ω ΩΛ SN type Ia (standard candles) m at z~0.5 are fainter than expected even if the Universe flux were empty Þ The cosmic expansion must have been accelerating since the light was emitted .. 4π = − Gρa(3w + 1) a 3 2 where p = wρc

ρtot = ρmass + ρrel + ρvac Perlmutter et al ‘98 -3 -4 a/a0=1/(1+z) € a a const Institute for Computational ? Cosmology € Evidence for Λ from high-z University of Durham supernovae Distant SN are fainter than expected if expansion were decelerating

Riess et al ‘98 Institute for Computational Cosmology Evidence for Λ from high-z University of Durham supernovae

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

Clocchiatti et al ‘06

Institute for Computational Cosmology University of Durham The cold dark matter cosmogony

So (implaussibly), we seem to need dark energy

But why cold dark matter?

Institute for Computational Cosmology Non-baryonic dark matter University of Durham candidates

Type candidate mass

hot neutrino a few eV

Sterile warm keV-MeV neutrino axion 10-5eV->100 cold neutralino GeV

Institute for Computational Cosmology The origin of cosmic structure University of Durham → QUANTUM FLUCTUATIONS: -35 Damping (nature Inflation (t~10 s) n≈1 + of dark matter)

→ FLAT UNIVERSE P(k)=Akn T2(k,t) Transfer function δρ/ superclusters clusters ρ galaxies ↓ ↓ ↓

P(k) Rh(teq) cold • Hot DM (eg ~30 ev neutrino) Meszaros damping - Top-down formation • Cold DM (eg ~neutralino)

n=1 - Bottom-up (hierachical) Free streaming

Large scales Small scales Institute for Computational Cosmology Neutrino (hot) dark matter University of Durham

Ων=1 (mν = 30 ev) Free-streaming length so large that superclusters form first and galaxies are too young

Zf=0.5 Zf=2.5 Neutrinos cannot make an appreciable CfA redshift survey contribution to Ω and m << 10 ev ν Frenk, White & Davis ‘83

Institute for Computational Cosmology Non-baryonic dark matter University of Durham cosmologies

Neutrino dark CDM matter produces Ω=0.2 unrealistic clustering

Early CDM N-body simulations gave Neutrinos promising results HDM ΩΩ=1=1

In CDM CfA redshift structure forms survey Davis,Davis, Efstathiou,Efstathiou, hierarchically FrenkFrenk && WhiteWhite ‘85‘85

Institute for Computational Cosmology The cold dark matter cosmogony University of Durham

Peebles ‘82

Davis, Efstathiou, Frenk & White 1985

Bardeen, Bond, Kaiser & Szalay 1986

Blumenthal, Faber, Primack & Rees 1984

Institute for Computational Cosmology University of Durham The cold dark matter cosmogony

Cold dark matter candidates:

-5 • Axion ma ~ 10 eV

• Sterile neutrino mν ~ 100 MeV

• Neutralino (lightest stable susy particle) mX > 100 GeV

Institute for Computational Cosmology Modelling large-scale structure Cosmological model (Ω, Λ, h…); dark matter

Primordial fluctuations Standard model: δρ/ρ(M, t) ΛCDM • Material content: Cold dark matter (eg neutralino;21%), baryons (4%), dark energy (Λ; 75%) Quantum fluctuations during inflation: 2 n • Initial conditions: |δk| k , n≈1; Gaussian amplitudes

• Growth processes: Gravitational instability Ω = 0.21, Ω = 0.04, Ω = 0.75, • Parameters: CDM b Λ h = 0.70,σ 8 = 0.9, ...

€ University of Durham

Testing ΛCDM on very large scales (and very early times)

Institute for Computational Cosmology The microwave background radiation 380 000 years after the big Bang

Plasma T=2.73 K

t=0

John Mather 2006 Nobel laureate t=380 000 yrs The microwave background radiation 380 000 years after the big Bang

inflation

Plasma T=2.73 K

z = ∞ z =1000 The CMB

University of Durham 1992

The cosmic microwave background radiation (CMB) provides a window to the universe at t~3x105 yrs In 1992 COBE discovered temperature fluctuations (ΔT/ T~10-5) consistent with inflation predictions

Institute for Computational Cosmology The CMB

University of Durham 1992

George Smoot - Nobel Prize 2006

Institute for Computational Cosmology The CMB

University of Durham 1992

George Smoot - Nobel Prize 2006

Institute for Computational Cosmology The CMB

University of Durham 1992

2003

Institute for Computational Cosmology WMAP temp anisotropies in CMB

University of Durham

Amplitude of fluctuations

The amplitude of the CMB ripples is exactly as predicted by inflationary cold dark matter theory The position of the first peak  FLAT UNIVERSE

Hinshaw etal ‘06 Institute for Computational Cosmology The Emergence of curvature the Cosmic Initial University of Durham 3-year data Conditions > 105 independent ~ 5s total baryons density measurements of T are fit by a priori model: LCDM

Polarization: TE x-power spectrum

T-P x-corr Adiabatic fluctns

Institute for Computational Cosmology The cosmic power spectrum: from University of Durham the CMB to the 2dFGRS

-1 -1 1000 k (comoving h Mpc) 10 ΛCDM provides an

excellent description of 3 CMB data mass power spectrum Mpc) from 10 -1000 Mpc -1 ΛCDM CMB: ?

• Convert angular separation to distance (and k) assuming flat geometry

• Extrapolate to z=0 Power spectrum P(k) (h using linear theory

-1 -1 Sanchez et al 06 wavenumber k (comovingInstitute for Computational h Mpc) Cosmology The 2dF Galaxy Redshift Survey 221,000 redshifts Sloan Digital Sky Survey

~500,000 galaxy redshifts Testing the CDM paradigm

University of Durham -5 P(k) Initial conditions : ΛCDM z=1000 δρ/ρ ∼10 δρ/ Cold dark matter z~100 ρ 0 Galaxies Clusters

n=1 Superclusters CMB ? Fluctuation amplitude

Large scales Small scales

The galaxy distribution evolves from by fluctuationns seen in CMB by gravitational z=0 amplification. δρ/ρ ∼1−106

Institute for Computational Cosmology Testing the CDM paradigm

University of Durham “Cosmology machine” P(k) δρ/ Cold dark matter ρ z~100 0 Galaxies Clusters

n=1 Simulations Superclusters CMB Fluctuation amplitude

Large scales Small scales Initial conditions : ΛCDM Basic DM physics simple: structure z=0 grows primarily by gravity δρ/ρ ∼1−106 N-body simulations Institute for Computational Cosmology University of Durham dalla Vechia, Jenkins & Frenk 150 Mpc/h

Comoving coordinates

Institute for Computational Cosmology The Millennium simulation University of Durham

Cosmological N-body simulation

• 10 billion particles

• 500 h-1 Mpc box

8 -1 UK, Germany, Canada, US • mp = 8×10 h Mo collaboration

• Ω =1; Ωm=0.25; Ω b=0.045; Simulation data available at: h=0.73; n=1; σ8 =0.9 http://www.mpa-garching.mpg.de/Virgo Carried out at Garching using 6 • 20 ×10 gals brighter than LMC Pictures and movies available at: L-Gadget by V. Springel www.durham.ac.uk/virgo (27 Tbytes of data)

Nature, June/05 Institute for Computational Cosmology Virgo consortium for

University of Durham supercomputer simulations Core members and associates . Carlos Frenk – ICC, Durham (P.I.) . Adrian Jenkins – ICC, Durham . Tom Theuns – ICC, Durham . Gao Laing – ICC, Durham . Simon White – Max Plank Institut für Astrophysik (co-P.I.) . Volker Springel – Max Plank Institut für Astrophysik . Frazer Pearce – Nottingham . Naoki Yoshida – Tokyo . Peter Thomas – Sussex . Hugh Couchman – McMaster . John Peacock – Edinburgh . George Efstathiou – Cambridge . Joerg Colberg – Pittsburgh . Scott Kay – Oxford Simulation data available at: . Rob Thacker – McGill http://www.mpa-garching.mpg.de/Virgo . Julio Navarro – Victoria . Gus Evrard – Michigan Pictures and movies available at: . Joop Schaye – Leiden www.durham.ac.uk/virgo

Institute for Computational Virgo junior associates Cosmology

Around 20 Phd students+postdocs The Millennium simulation University of Durham

Cosmological N-body simulation

• 10 billion particles

• 500 h-1 Mpc box

8 -1 UK, Germany, Canada, US • mp = 8×10 h Mo collaboration

Nature, June/05 Institute for Computational Cosmology The mass power spectrum University of Durham

z=0 The non-linear mass z=1 power spectrum is accurately determined z=3.05 by the Millennium linear non-linear simulation over large growt evolution h

range of scales (k) z=7 2

Δ z=14.9

linear theory

k [h/Mpc]

Institute for Computational Cosmology z = 0 Dark Matter

University of Durham Populating the MS with galaxies

Semi-analytic modelling • Find dark matter halos • Construct halo merger trees • Apply SA model (gas cooling, star formation, feedback)

Springel etal 05 Institute for Computational Cosmology z = 0 Galaxy light

University of Durham

Croton et al 06 Institute for Computational Cosmology University of Durham 14 10 Mo Dark matter Galaxies

Institute for Computational Cosmology SDS real S

CfA 2dFGRS

simulated

Springel, Frenk & White Nature, April ‘06 Real and simulated 2dF galaxy survey

University of Durham

 Real Simulated 

Institute for Computational Cosmology The final 2dFGRS power spectrum University of Durham

2dFGRS P(k) well fit by ΛCDM ΛCDM model model convolved with window ΛCDM convolved function with window

Cole, Percival, Peacock,

Baugh, Frenk + 2dFGRS ‘05 Institute for Computational Cosmology The 2dF Galaxy Redshift Survey A collaboration between (primarily) UK and Australia 250 nights at the AAT

 221,000 redshifts

to bj<19.45 median z=0.11 Survey complete and catalogue released in July/03 Sloan Digital Sky Survey ~500,000 galaxy redshifts University of Durham

Springel etal 05 Institute for Computational Cosmology The mass power spectrum University of Durham

z=0 The non-linear mass z=1 power spectrum is accurately determined z=3.05 by the Millennium simulation over large

range of scales (k) z=7 2

Δ z=14.9

linear theory

k [h/Mpc]

Institute for Computational Cosmology CMB anisotropies and large-scale University of Durham structure

Institute for Computational Cosmology CMB anistropies and large-scale University of Durham structure

Meiksin etal 99 2dFgrs

Institute for Computational Cosmology Millennium simulation Baryon wiggles in the galaxy distribution

Power spectrum from MS divided by a baryon-free LCDM spectrum z=7 z=3 Galaxy samples DM gals matched to plausible large observational surveys at given z z=1 z=0 Springel et al 2005 The final 2dFGRS power spectrum University of Durham

2dFGRS P(k) well fit by ΛCDM ΛCDM model model convolved with window ΛCDM convolved function with window

Cole, Percival, Peacock,

Baugh, Frenk + 2dFGRS ‘05 Institute for Computational Cosmology The final 2dFGRS power spectrum University of Durham P(k) / Pref(Ωbaryon=0) Baryon oscillations conclusively detected in ΛCDM model 2dFGRS!!! Demonstrates that structure grew by gravitational instability in ΛCDM universe

Also detected in ΛCDM convolved SDSS LRG sample with window (Eisenstein etal 05) Cole, Percival, Peacock,

Baugh, Frenk + 2dFGRS ‘05 Institute for Computational Cosmology SDSS LRG correlation function University of Durham

Again, CDM models fit the correlation function adequately well (although peak height is s)

slightly too large; ξ ( assuming ns=1, h=0.72)

2 Ωbh =0.024, 2 Ωmh =0.133±0.011,

⇒ Ωb/Ωm= 0.18

Eisenstein et al. 05

Institute for Computational Cosmology Baryon oscillations in the power spectrum University of Durham

Comoving sound horizon at trec

2 (depends mostly on Ωmh 2 and weakly on Ωbh )

“wavenumber” of acoustic oscillations: kA= 2π/s

Comoving distance/redshift:

2 (depends on Ωmh and w) Apparent size of standard ruler depends on cosmology ⇒ dark energy eqn of state w

(e.g. Eisenstein & HU 1998; Blake & Glazebrook 2003, 2005; Institute for Computational Seo & Eisenstein 2003; 2005……) Cosmology Baryon oscillations in the power spectrum University of Durham

What are the prospects for determining kA in realistic surveys?

What is the optimal strategy?

Institute for Computational Cosmology N-body simulations of large University of Durham cosmological volumes

BASICC

L=1340/h Mpc

N=3,036,027,392

20 times the Millennium volume

Halo resolution: (10 particle limit) 5.5 e+11/h Mpc

130,000 cpu hours on the Cosmology Machine

Angulo, Baugh,Institute Frenk for Computational & Lacey ‘07 Cosmology Non-linear evolution of University of Durham matter fluctuations

BASICC simulation dark matter real space (k)

linear P(k) divided by linear theory P(k),

P(k)/P scaling out growth factor

Angulo, Baugh, Frenk & Lacey ‘07

Institute for Computational Cosmology Non-linear evolution of University of Durham matter fluctuations

Log (P(k)/Plinear(k)) at z=1

Angulo, Baugh, Frenk & Lacey ‘07

Institute for Computational Cosmology Redshift space distortions University of Durham Peculiar motions distort clustering pattern

Coherent bulk flows boost large scale power (Kaiser 1987)

Motions of particles inside virialised structures damp power at high k

Institute for Computational Cosmology Redshift space distortions University of Durham

Peculiar motions distort Redshift space clustering pattern

12 Halos M> 10 Mo Boost in power on large scales due to coherent flows

Dark matter Damping at higher k affects DM but not the halos

In z-space, halo bias is scale-dependent

Institute for Computational Cosmology Galaxy bias in real space University of Durham

Magnitude limited sample.

Galaxy clustering boosted relative to mass in real space

Angulo, Baugh, Frenk & Lacey ‘07

Institute for Computational Cosmology Galaxy bias in real space University of Durham

Boost in clustering approximates to a constant bias factor on large scales.

Angulo, Baugh, Frenk & Lacey ‘07

Institute for Computational Cosmology Galaxy bias in redshift space University of Durham

Galaxy P(k) cannot be reproduced by multiplying mass P(k) by constant factor in redshift space.

⇒ In z-space, galaxies have a scale-dependent bias out to k~0.1

Institute for Computational Cosmology Galaxy bias in redshift space

University of Durham

Comparison of different selections e.g. colour, emission line strength

Angulo et al ‘07

Institute for Computational Cosmology Projected BAO data for University of Durham planned surveys at z=1

Projections based on mock catalogues made from large N-body simulation plus semi-analytic galaxy formation model

Institute for Computational Cosmology Constraints on w from SnIa,

University of Durham WMAP and 2dFGRS

Cosmological w constant

Assume w=const (cosmological constant)

w w=-0.9 ± 0.1

Ωm Ωm Spergel et al 2006 Institute for Computational Cosmology Headline forecasts for w University of Durham Survey Error in w

WiggleZ 5.0 - 9.5 %

WFMOS 3.6 - 4.0 %

Pan-STARRS 0.03 photo-z 1.6 - 3.5 % 0.06 photo-z 2.2 - 4.9 %

DUNE 3% photo-z 1.2 - 2.5% 20,000 sq deg

SPACE 0.25 - 0.5% 109 galaxies 27,000 sq deg Angulo et al 07 Institute for Computational Cosmology The cosmic power spectrum: from University of Durham the CMB to the 2dFGRS

-1 -1 CMB: 1000 k (comoving h Mpc) 10 • Convert angular z=0 3 WMAP separation to distance

(and k) assuming flat Mpc) -1 ΛCDM geometry 2dFGRS • Extrapolate to z=0 using linear theory ⇒ ΛCDM provides an ? excellent description of mass power spectrum Power spectrum P(k) (h from 10-1000 Mpc

-1 -1 Sanchez et al 06 wavenumber k (comovingInstitute for Computational h Mpc) Cosmology University of Durham

z = 0.0 Institute for Computational Cosmology The Density Profile of Cold Dark

University of Durham Matter Halos ) 3 Halo density profiles are independent of halo mass & kpc

o cosmological parameters

M There is no obvious density 10 Galaxy clusters plateau or `core’ near the centre. Dwarf galaxies (Navarro, Frenk & White ‘97) Log density (10

Institute for Computational Log radius (kpc) Cosmology A cold dark matter universe University of Durham

N-body simulations show that cold dark matter halos (from galaxies to clusters) have:

• “Cuspy” density profiles • Large number of self-bound substructures (10% of mass)

This has led to two well-publicized “problems”:

• The “halo core’’ problem • The “satellite” problem

Institute for Computational Cosmology Explanations for the core/satellite "crises" University of Durham

• 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

Institute for Computational Cosmology A Cold dark matter universe University of Durham

N-body simulations show that cold dark matter halos (from galaxies to clusters) have:

• “Cuspy” density profiles • Large number of self-bound substructures (10% of mass)

This has led to two well-publicized “problems”:

• The “halo core’’ problem • The “satellite” problem

Institute for Computational Cosmology The “halo core’’ problem University of Durham ) 3 Halo density profiles are independent of halo mass & kpc

o cosmological parameters

M There is no obvious density 10 Galaxy clusters plateau or `core’ near the centre. Dwarf galaxies (Navarro, Frenk & White ‘97) Log density (10

Institute for Computational Log radius (kpc) Cosmology A galactic dark matter halo University of Durham

Springel, Jenkins, Helmi, •60 million particles inside rvir Navarro, Frenk & White ‘07 Institute for Computational Cosmology N=8003

NF W crit ρ (r)/ ρ

NFW profile is a good fit to ρ(r) down to ~0.1% rvir

r/h-1kpc Springel, Jenkins, Helmi, Navarro, Frenk & White ‘06 The density profile of galaxy University of Durham cluster dark halos

Do real dark halos have the profiles found in the simulations?

Profiles can be probed by:

• Gravitational lensing and/or X-ray emission in clusters

Galaxy changes ρ(r) • Galaxy rotation curves → messy Halos are triaxial

Institute for Computational Cosmology The central density profile of

University of Durham galaxy cluster dark halos Inner DM density profile inferred from X-ray data (Chandra) A1795 (z=0.0632)

NFW Mass within r A1795 Ettori etal 02

Profile shallower than Ettori etal 02 r (kpc) NFW (β = 0.59 ±0.15) Institute for Computational Cosmology The central density profile of University of Durham galaxy cluster dark halos X-ray data

Mass profile of galaxy NF clusters, from X-ray W data & assumption of hydrostatic equilibrium c ρ / NF W

Excellent agreement with CDM halo

predictions r/r500 Institute for Computational Vikhlinin et al ‘06 Cosmology Mass profile in cluster cores University of Durham from strong lensing

MS 2137-23 Lum matter

DM Total matter tan arc density

vel dis rad arc r (kpc) • Assume spherical symmetry Sand etal 05

• Model potential as power-law DM + galaxy with constant M/L

• Constrain inner slope of DM profile using tangentialInstitute for Computationalarc, Cosmology radial arc and velocity dispersion profile Mass profile in cluster cores University of Durham from strong lensing

−β β −3 ρ(r) ∝ r (rs + r) β=1 for NFW NFW Moor e

€ Sand et al find β=0.5, in disagreement with CDM probability

DM inner slope (β) Sand et al 04

Institute for Computational Cosmology Cuspy Cold Dark Matter Halos

University of Durham

Institute for Computational Cosmology Mass profile in cluster cores

University of Durham from strong lensing

−β β −3 ρ(r) ∝ r (rs + r) Actual β β=1 for NFW Recovered β For this simulation, β=1.2 € Elliptical model probability Sand etal (spherically symm) probability analysis returns β~0.5!!!

Reason: Sand et al assume spherical symmetry

DM inner slope (β)

Meneghetti, Bartelmann, Frenk & Jenkins ‘07 Institute for Computational Cosmology University of Durham

The “halo-core problem” ?

The inner profiles of cluster halos seen consistent with the cusps predicted in ΛCDM

Institute for Computational Cosmology A Cold dark matter universe University of Durham

N-body simulations show that cold dark matter halos (from galaxies to clusters) have:

• “Cuspy” density profiles • Large number of self-bound substructures (10% of mass)

This has led to two well-publicized “problems”:

• The “halo core’’ problem • The “satellite” problem

Institute for Computational Cosmology The satellites of the Local Group University of Durham

The Local Group contains only about 40 bright satellites

N-body simulations produce 1000s of small subhalos

Moore etal ‘99 Institute for Computational Cosmology Substructure in cold dark matter halos University of Durham

Springel, Jenkins, Helmi, •60 million particles inside rvir Navarro, Frenk & White ‘07 Institute for Computational Cosmology University of Durham Feedback in galaxy formation

Effects of Universe was reionized at z~10 reionization

Gas is neutral → cools in small halos

First gals First H is reionized at stars z~(10-6)

Gas heated ~104K → cannot cool in halos with V<40 km/ s

From STSci picture gallery Institute for Computational Cosmology Baryon habitats University of Durham No photo-heating Simple photo-heating (non-radiative) 4 model: Tfloor=2x10 K at z=11

Prevents collapse of Photo-heating baryons in halos with

V200< 35 km/s 10 (M200<10 Mo) Baryon fraction

-1 log M200[h Mo] Crain, Eke, Frenk, Jenkins, McCarthy, Navarro & Pearce 07 Institute for Computational Cosmology Substructure in cold dark matter halos University of Durham

Only the few small subhalos that formed before reionization can cool gas and make a visible galaxy

Springel, Jenkins, Helmi, •60 million particles inside rvir Navarro, Frenk & White ‘07 Institute for Computational Cosmology Luminosity Function of Local University of Durham Group Satellites

• Photoionization inhibits ΛCDM the formation of satellites Koposov et al ‘07 • Abundance reduced by No photo-i factor of 10! Photo-i • Median model gives correct abundance of sats brighter than M =-9, V > 12 km/s V cir LG data • Model predicts many, as yet undiscovered, faint satellites

Benson, Frenk, Lacey, Baugh & Cole ’02 Institute for Computational (see also Kauffman etal ’93, Bullock etal ’01) Cosmology The satellites of the Milky Way University of Durham

The 11 bright satellites within 250 kpc of the Milky Way lie roughly on a great circle on the sky (Lynden-Bell ‘67, Kroupa, etal ‘05)

Sculptor, Draco, Leo I & II Sextans

LMC, SMC, Ursa Minor Sagittarius Dw

Carin a Fornax

Institute for Computational Cosmology The satellites of the Milky Way University of Durham

The 11 bright satellites within 250 kpc of the Milky Way lie on a great circle on the sky (Lynden-Bell ‘67, Kroupa, etal ‘05)

Milky Way’s disk is perpendicular to the great circle

Institute for Computational Cosmology The satellites of the Milky Way University of Durham

The 11 bright satellites within 250 kpc of the Milky Way lie on a great circle on the sky (Lynden-Bell ‘67, Kroupa, etal ‘05)

Institute for Computational Cosmology Simulations of disc galaxy formation University of Durham ΛCDM initial conditions gas star s

Smooth Particle Hydrodynamics (SPH)

Okamoto, Jenkins, Eke, & Frenk ‘05 Institute for Computational Cosmology University of Durham

Institute for Computational Cosmology The satellites of the Milky Way University of Durham

The 11 bright satellites within 250 kpc of the Milky Way lie on a great circle on the sky (Lynden-Bell ‘67, Kroupa, etal ‘05)

In 2/3 simulations, satellites system is nearly perpendicular to disk (within 20o)

Institute for Computational Cosmology University of Durham

z = 0.0 Institute for Computational Cosmology Substructure in cold dark matter halos University of Durham

Springel, Jenkins, Helmi, •60 million particles inside rvir Navarro, Frenk & White ‘07 Institute for Computational Cosmology Substructure in CDM halos University of Durham

Halos have large number of self-bound substructures containing ~10% of the masss and with d N / d M ~ M - 1.8

Gravitational lensing effects → Substructures may be observable γ -ray annihilation emission

Anomalous flux ratios in multiply- imaged quasars ⇒ Substructure Dalal & Kochanek ‘02, Metcalfe & Zhao ‘02 Institute for Computational Cosmology Conclusions: the ΛCDM model University of Durham

ΛCDM 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  Baryon acoustic oscillations detected in 2dFGRS and SDSS  Current generation of surveys to detect BAO at z~1 will constrain w but only to ~5%  Data consistent with cusps in cluster halos  “Satellite problem” probably solved by photoionization Institute for Computational Cosmology University of Durham The “golden” era in cosmology is not over

It has probably just begun!

Institute for Computational Cosmology