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Cosmology : Cosmic Microwave Background & Large scale structure
Cosmology : Cosmic Microwave Background & Large scale structure
Tarun SouradeepI.U.C.A.A.
Cosmology
IUCAA VSP program
(May 18-22, 2012)
Lec. 2:• Cosmic Content• Perturbed Universe
Simple… yet, an exotic universe
• 95% of the energy of the universe is in some exotic form
• Dark Matter: we cannot see it directly, only via its gravitational affect. Clusters under gravity. 73%
• Dark Energy: smooth form of energy that we cannot repulsively under gravity. 23%
• Ordinary (baryonic) matter accounts for 4%
• Know 99% the radiation content of the universe (CMB)Insignificant now (0.01%) but important prior to z<10000
Evolution of thought:
Matter budget of the cosmos
Fig:NASA/WMAP science team
Fig:NASA/WMAP science team
Matter budget of the Universe Matter budget of the Universe
w=0Decelerated Expansion
(Grav. Clustering)
w=0 (w<-1/3)Decelerated Expansion (Non-Clustering)
Ordinary matter is sprinkled on the Cold Dark matter distribution
Galaxies light up at the densest points
Where is the Cold Dark matter ?
6 times more in dark matter than‘baryonic’ matter
Zwicky 1935
Dark matter in Galaxies !
2
2
( )v GM rm m
r r
2
2
( )v GM rm m
r r
34( ) for
3 for tot
M r r R
M r R
r
( )
4for
3
for totGMr R
r
r
RrG
v r
R
Rotation of Spiral Galaxies !!!
Dark matter in our own backyard !?!
Dark matter in the Milky way
Dark matter in other galaxies too !!
Dark matter in clusters !?!
Hot gas in clusters
Coma cluster
Hot gas in clusters
Virgo cluster
Marbles in a glass bowl !!!
Velocity dispersion of galaxies in a cluster
Measures the depth of its gravitational potential
Speeding galaxies in a cluster
Gravitational lensing Gravitational lensing
Distant galaxies beyond a cluster are lensed….
Bullet cluster
Bullet cluster movie
Evidence for Dark Energy?
Is it the Cosmological constant?
The Cosmic repulsive force Einstein once proposed and later denounced
as his ‘biggest blunder” ?
Theoretical possibilitiesPossibility 1: Universe permeated by energy density, constant in time
and uniform in space (Einstein’s L).
Possibility 2: DE some kind of ‘unknown’ dynamical fluid. Its eqn of state
varies with time (or redshift z or a = (1+z)-1).
Impact of DE (or different theories) can be expressed
in terms of different “evolution of equation of state” w(a) = p(a) / r(a) with w(a) = -1 for .L
Possibility 3: GR incorrect, modified Lagrangian, Braneworld scenario
(higher derivative/dimensional gravity)
Possibility 4: `Inhomogeneous’ cosmos – backreaction of
gravitational. Instability (UNLIKELY)
Geometry, Expansion & MatterGeometry, Expansion & Matter
Dark energy causes accelerated expansion
...)1(2
12
2
00
c
vq
c
vDH L
Correction to the Hubble’s Law
…. measures the acceleration in the expansion of the universe
Measure distances independent of redshift v/c
till v/c=z~1
c
vDH L 0
10 mFlux
5 m
Measuring distance using standard candles
4 Flux
Supernova in a galaxy: standard candle
Supernova can be seen in distant galaxies
Supernova in a very distant galaxy
• Starlight from Galaxies
• Stuff we are made of!!
• Light elements from early hot universe
• Low CMB temperature fluctuations
• Accelerated expansion of the universe (High redshift SN)
• Structure formation scenario compatible with observations
• Rotation of galaxies
• Speeding galaxies in clusters
• Gravitational lensing
• Hot gas in clusters
Matter budget of the cosmos
Fig:NASA/WMAP science team
How do we know so much now about this
model Universe ?
Perturbed universe!
Transparent universe
Opaque universe
14 GPc
Here & Now(14 Gyr)
0.5 Myr
Cosmic “Super–IMAX” theater
After 25 years of intense search, tiny variations (~10 p.p.m.) of CMB temperature sky map finally discovered.
“Holy grail of structure formation”
Predicted as precursors to the observed large scale structure
The Perturbed Universe The Perturbed Universe Cosmic Microwave Background Anisotropy
George SmootJohn Mather
COBE
Cosmic Background Explorer
First detection of CMB
anisotropy (1992)
Temperature anisotropy T + two polarization modes E&B Four CMB spectra : Cl
TT, ClEE,Cl
BB,ClTE
CMB Anisotropy & Polarization
CMB temperature Tcmb = 2.725 K
-200 K < T < 200 K Trms ~ 70 K
D TpE ~ 5 KD TpB ~ 10-100 nK
)2sin()2cos()( kbkaTk
kk
k Recall Fourier series
Hence, a powerful tool for constraining cosmological parameters.
Fig. M. White 1997
The Angular power spectrum of CMB anisotropy dependssensitively on Cosmological parameters
lC
Multi-parameter Joint likelihood (MCMC)
• Low multipole : Sachs-Wolfe
plateau
• Moderate multipole : Acoustic
“Doppler” peaks
• High multipole : Damping tail
Dissected CMB Angular power spectrum
(fig credit: W. Hu)
CMB physics is verywell understood !!!
Music of the Cosmic Drum
Perturbed universe: superposition of random `pings’
Perturbed universe: superposition of random `pings’
(Fig: Einsentein )
Ping the ‘Cosmic drum’
More technically,the Green function (Fig: Einsentein )
150 Mpc.
Ripples in the different constituents Ripples in the different constituents
150 Mpc.
(Einsentein et al. 2005)
Fig:Hu & Dodelson 2002
Sensitive to curvature
K1220l
l
CMB Angular power spectrum
Fig:Hu & Dodelson 2002
Sensitive to Baryon density
KT 74
CMB Angular power spectrum
2003 Second NASA CMB Satellite mission
First NASA CMB Satellite mission
NASA Launched July 2001
Wilkinson Microwave Anisotropy Probe
NASA/WMAP science team
Covers 30% sky daily,
Whole sky in 6 months
WMAP CMB mission
WMAP data:
7 year: Jan 26, 2010
5 year: Feb 6, 2008
3 year: Mar, 2006
1-year Feb, 2003
NASA : Launched July 2001
K band 23 GHz
Ka band 33 GHz
Q band 41 GHz
V band 61 GHz
W band 94 GHz
CMB anisotropy signal
WMAP multi-frequency maps
-200 K < T < 200 K Trms ~ 70 K
CMB temperature Tcmb = 2.725 K
Saha, Jain, TS 2006
WMAP map of CMB anisotropy
Independent, self contained analysis of WMAP multi-frequency maps
Saha, Jain, Souradeep(WMAP1: Apj Lett 2006)
WMAP3 2nd release : TS,Saha, Jain: Irvine proc.06Eriksen et al. ApJ. 2006
WMAP: Angular power spectrum
Good match to WMAP
team
IIT Kanpur + IUCAA
(48.3 1.2, 544 17)
(48.8 0.9, 546 10)
(41.7 1.0, 419.2 5.6)
(41.0 0.5, 411.7 3.5)
(74.10.3, 219.80.8)
(74.7 0.5, 220.1 0.8
Characteristic size & amplitude of hot/cold spots in the CMB
map
(Saha, Jain, Souradeep Apj Lett 2006)
Flat Universe
Hyperbolic Universe
Spherical Universe
Geometry of the Universe is FLAT
WMAP 5 & 7: Angular power spectrum
3rd peak
Fig.: Tuhin Ghosh
Current Angular power spectrum
Image Credit: NASA / WMAP Science Team
3rd peak
6thpeak
4th peak
5th peak
Standard cold dark matter
Cosmological constant + cold dark matter
Gravitational Instability
( now )(quarter size ) (half size)
Time
expansion (fig: Virgo simulations)
NASA/WMAP science team
Age of the universe
Dark energy density
Dark matter density
Expansion rate of the
universe
Good old Cosmology, … New trend !Total energy
density Baryonic
matter density