MATTEO VIEL

STRUCTURE FORMATION

INAF and INFN Trieste

SISSA - 3rd March and 7th March 2011

OUTLINE: LECTURES

1. Structure formation: tools and the high redshift universe

2. The dark ages and the universe at 21cm

3. IGM cosmology at z=2=6

4. IGM astrophysics at z=2-6

5. Low redshift: gas and galaxies

6. Cosmological probes LCDM scenario

OUTLINE: LECTURE 2

Physics of 21cm transition in the high redshift universe

LOFAR cosmological perspectives

SKA cosmological perspectives

Review: Furlanetto, Oh, Briggs (2006)

Cosmic history

30-240 MHz window z = 5-46 about 90 % of the age of the universe

?

Main characters: DM haloes +…..

Mo & White 2002

LOFAR

Physics at 21cm - I

Three processes determine Ts:1- absorption of CMB photons timescale of eq 3x105 yrs/1+z2- collisions with other hydrogen atoms, free electrons and protons C10-C01 Important in dense gas

3- scattering of UV photons P10-P01

Line profile

xc coupling coefficient for collisionsx coupling coeffictiont for UV scattering – WF eff.

Spontaneous emission 10-15 s

Ts = spin temperature definition Almost all astrophysical processeshave Ts >> T*

Physics at 21cm - II

Differential brightness temperature of spin against CMB

If T s >> T it saturates to a given value but if T s < T can be arbitrary large

Physics at 21cm - III

Heating per baryon by i-th process: compton,X-ray heating, Lyman-alpha

Compton heating drives Tk-TTill recombination time exceeds expansion time-scaleThen matter and radiation decouple

T K ~ 1+z

T K ~ (1+z)2

Expansion term

T ~ 1+z coupled with CMB radiationT ~ (1+z)2 matter expanding adiabatically

Physics at 21cm: Atoms and photons - IV

z dec = Compton heating becomes inefficient and T K < T for the first time ~ 150 (b h2/0.023)2/5 This is the thermal decoupling redshift

Z coll = Density below coll At this point T s T and the signal vanishes. This is produced by collisions and x c = 1

z h = redshift at which the IGM is heated above T

z c = redshift at which x=1 and T s and T K are coupled

z r = reionization redshift

ATOMIC PHYSICS

LUMINOUS SOURCES

Physics at 21cm: Emission or absorption - V

Absorption or emission: crucial input is of course ionization fraction

Semi-analytical model for reionization (see review or Crociani et al. 08)

Ionization fraction

Ionization efficiency

Star formation / escape fraction / number of ionizing photons per baryon

Collapse fraction from PS

Recombination coefficient / Clumping factor

During reionization heat input is

How would the universe at z~12 look like? LCDM DARK ENERGY

Tsujikawa 08

How would the universe at z~12 look like - II? LCDM LCDM + different physics for galaxy formation

Galactic winds + multiphaseStar formation criterion

How would the universe at z~12 look like - III? LCDM DARK ENERGY

Gas overdensity

Neutral hydrogen fraction

SKY AND FREQUENCY INFORMATION

Radio sky much brighterthan CMB

Probability distribution functions

Number of haloes

z = 12

Pdf and correlation function

Tozzi et al. 2001Ciardi & Madau 2003

High redshift pdf reflects density in the linear regimeLow redshift signal is dominated by ionization fraction

Lya photons suceed in decoupling the CMB and spin temperature at very high redshift

1 arcmin ~ 2 com Mpc/h at z=12

IGM tomography at high redshift: expansion

Observable: brightness temperature fluctuations in SPACE and FREQUENCY :

(x) = [T b (x) – T b] / T b

Expanding to linear order:

= bxxpecvel

Baryons/neutral fraction/Ly- coupling/Kinetic gas temperature

Furlanetto, Oh, Briggs (2006)

z c = 18 and z h = 14 and z r = 7

Coefficients are complicated….. And are intrinsically gastrophsyical….

IGM tomography at high-z: Cosmological parameters

Mc Quinn et al. 2006

1- density fluctuations dominate the signal xi0 TCMB<<TS

2- bubbles are present and contaminate the signal but P6 and P4 are significant3- at very large scales where ionization fluctuations are unimportant

Noise + sample variance: SKA black, MWA blue, LOFAR red

Thin line is signal for xi<<1 and TS >>TCMB

IGM tomography at high-z: growth factors

Signal isotropy is broken by: - different scaling of transverse and parallel distance ALCOCK-PACZYINSKI (AP) TEST - redshift space distortions

= 2 f b+

isotropic

P(k) = 4 P(k) + 2 2 P (k)iso + P(k) iso iso

The power is boosted and most importantly power of density perturbations can be isolated

w(z) = w0 + w a (1+z)

IGM tomography at high redshift: powerspectra

1 – boosting factor 2- since the power depend on the angle one can evaluate the power at different values of the angle and isolate the different contributions

Matter

McQuinn et al. 2006

IGM tomography at high redshift: AP and NG

AP test: Nusser (2005) MNRAS, 364, 743

1/H

D n

orm

aliz

ed

to s

tan

dard

mod

el

Non gaussianity: Pillepich, Porciani, Matarrese (2006)

Cooray (2006)

subarcminute angular resolution needed !!

Factor 10 better than the CMB

(x)= L (x) + f NL(2

L(x)-<2

L(x)>)

Few arcsec resolution - LOFAR extended?

But small f sky (LOFAR-120 fsky=0.5)

z ~ 50

z ~ 20

Mhz

real space

Eke & 2dFGRS 2003

Peculiar velocities Peculiar velocities manifest themselves in manifest themselves in galaxy surveys as galaxy surveys as redshift-space distortionsredshift-space distortions

Peculiar velocities

redshift space

Line of sight to observer

Peculiar velocities manifest themselves in galaxy surveys as redshift-space distortions

Moreover, measuring separations parallel and perpendicular to the l.o.s. requires assuming a cosmological model that may be different from the true one

Peculiar velocities-II

The same argument holds true for the 21cm brightness temperature maps.

Measuring the 2-point correlation function in the direction parallel and perpendicular to the l.o.s. on can constrain:

- The growth rate of density fluctuations from redshift distortions.

-The expansion rate of the universe (and the cosmological parameters andM) from geometry-induced distortions (the Alcock-Paczynski effect).

Line of sight to observer

T21

(i)

T21 (j)

Mesinger & Furlanetto 07Peculiar velocities-III

Pair separation perpend. to line-of-sight rp (Mpc/h)

Redshift-space Temperature-Temperature correlation Redshift-space Temperature-Temperature correlation functionfunction

1420GHz

c

1 z

rp H(z)DA (z)

Pair

separa

tion

alo

ng lin

e-o

f-si

gh

t (

h-1 M

pc)

Figures by

Marco Pierleoni

s

rp

No redshift distortions

Model:Redshift: z=8m=0.25, =0.75f(m)= (m)0.55/b=0.5b=2100 km/s

Pair separation perpend. to line-of-sight rp (Mpc/h)

Redshift-space Temperature-Temperature correlation Redshift-space Temperature-Temperature correlation functionfunction

1420GHz

c

1 z

rp H(z)DA (z)

Pair

separa

tion

alo

ng lin

e-o

f-si

gh

t (

h-1 M

pc)

Linear redshift distortions only.Flattening proportional to growth rate of density fluctuations.

Pair separation perpend. to line-of-sight rp (h-1 Mpc)

Redshift-space Temperature-Temperature correlation Redshift-space Temperature-Temperature correlation functionfunction

1420GHz

c

1 z

rp H(z)DA (z)

Pair

separa

tion

alo

ng lin

e-o

f-si

gh

t (

h-1 M

pc)

Redshift distortions generating small-scale “spindle” due to nonlinear motions withinvirialized regions (100 km/s)

Pair separation perpend. to line-of-sight rp (h-1 Mpc)

Redshift-space Temperature-Temperature correlation Redshift-space Temperature-Temperature correlation functionfunction

1420GHz

c

1 z

rp H(z)DA (z)

Pair

separa

tion

alo

ng lin

e-o

f-si

gh

t (

h-1 M

pc)

Geometry distortions(AP effect) from having assumedm=1.00,=0.00

Pair separation perpend. to line-of-sight rp (h-1 Mpc)

Redshift-space Temperature-Temperature correlation Redshift-space Temperature-Temperature correlation function function

1420GHz

c

1 z

rp H(z)DA (z)

Pair

separa

tion

alo

ng lin

e-o

f-si

gh

t (

h-1 M

pc)

All distortionsincluded

MEASURING DENSITY FLUCTUATIONS

Could be doable over a significant fraction of the cosmic time finding deviations from LCDMand measuring the dark energy at early stages (if any)

Subarcminute resolution will be important (extended LOFAR)

--Measuring geometrical distortions in the iso-correlation Measuring geometrical distortions in the iso-correlation contours of the 21 cm maps around the epoch of re-contours of the 21 cm maps around the epoch of re-ionization allows to discriminate among competing dark ionization allows to discriminate among competing dark energy models.energy models.

-Measuring dynamical distortions in the iso-correlation -Measuring dynamical distortions in the iso-correlation contours of the 21 cm maps around the epoch of re-contours of the 21 cm maps around the epoch of re-ionization allows to break the degeneracy between Dark ionization allows to break the degeneracy between Dark Energy and Modified Gravity models and test the Energy and Modified Gravity models and test the gravitational instability picture.gravitational instability picture.

ALCOCK-PACZINSKI TEST

However, the task is observationally challenging, unless density fluctuations dominate over fluctuations in the neutral hydrogen fraction

A significant improvement can be obtained by cross-correlating the 21 cm mapwith deep galaxy redshift surveys. Results will depend on the relative bias ofHI and galaxy which, however, can be determined self-consistently from the data

SKA and galaxies -I

Blake, Abdalla, Bridle, Rawlings, 2004, aph-0409278Rawlings et al., 2004, aph-0409479Seo & Eisenstein 2003, ApJ, 598, 720Abdalla & Rawlings, 2005, MNRAS, 360, 27

SKA P(k) estimates not correlated small k-window function good

to probe features in the P(k) V SKA = 500 V 2dF

New regimes:Big volumes (small k) and high z (large k not affected by non linearities)

Survey requirements big fraction of the sky

- HI emission line survey - 109 (fsky/0.5) HI galaxies up to z=1.5 - probably the smallest masses probed

will be 5x109 Msun - Shown is a model for which Mbar ~ AM DM

WMAP PLANCK

0.5-1.4 GHz survey with large FOV

SKA and dark energy -II

Ultimate goal is again to constrain the dark energy properties at high z

Note that due to intrinsic degeneracies (w-m) the CMB alone (PLANCK) cannot probe w better than 0.1

SKA and weak lensing -III

Cosmic shear survey: high image quality (shape measurement), high source surface density, wide area

Advantages: point spread function for radio telescopes is stable, 1010 (fsky/0.5) sources good resolution 0.05 arcsec at 1.4 GHz, 30 nJy in a 4 hrs pointing

Disadvantage: unknown radio source population

The goal is to estimate the lensing power spectrum and derive cosmological parameters

SHEAR ALONE z=10,15SHEAR ALONE z=10,30,100

Blake et al. 2004 Metcalf & White 2006

F sky=0.5200 sources/sqarcmin

SUMMARY

SKA will probably be the most powerful dark energy probe and its accurate measurement of the P(k) will offer insights on the nature of dark matter; sinergies with particle physics

(inflation and elementary particles) will be fundamental

Effects of dark energy through ISW effectPhysics of inflationAdiabatic/isocurvature fluctuationsGaussianityFeatures in the P(k)Geometry/topology of the Universe

LOFAR extended with large field of view will probably we able to map

HI at z=12 (120 Mhz) with arcsec resolution allowing first studies of the topics above

SUMMARY

1 – Atomic physics of 21 cm and implication for astrophysics (light) and cosmology (matter) in the high redshift universe

2 – cosmological tests (AP test) and the power spectrum

3 – Reionization highlights in standard and non-standard structure formation scenarios (dark energy, non gaussianities etc.)