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