Observing the First Galaxies and the Reionization Epoch Steve Furlanetto UCLA

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Observing the First Galaxies and the Reionization Epoch

Steve Furlanetto

UCLA

February 5, 2008

Outline

Introduction: Observing Reionization

Galaxy Surveys

Current observations of LAEs

The Clustering Signature

The 21 cm Transition as a Cosmological Probe

Basic Physics

The Mean 21 cm Background

Measurements and Challenges

The Pre-reionization IGM

Reionization

Conclusion

A Brief History of the Universe

Big Bang

Last

Scattering

 Last scattering: z=1089, t=379,000 yr

Dark Ages

 Today: z=0, t=13.7

Gyr

First

Galaxies

Reionization

 Reionization: z=6-20, t=0.2-1 Gyr

Galaxies,

Clusters, etc.

 First galaxies: ?

G. Djorgovski

Reionization

First stars and galaxies produce ionizing photons

Ionized bubbles grow and merge

Affects all baryons in the universe

Phase transition

Mesinger & Furlanetto

Reionization

First stars and galaxies produce ionizing photons

Ionized bubbles grow and merge

Affects all baryons in the universe

Phase transition

Mesinger & Furlanetto

Reionization

First stars and galaxies produce ionizing photons

Ionized bubbles grow and merge

Affects all baryons in the universe

Phase transition

Mesinger & Furlanetto

Reionization

First stars and galaxies produce ionizing photons

Ionized bubbles grow and merge

Affects all baryons in the universe

Phase transition

Mesinger & Furlanetto

Reionization:

Observational Constraints

 Quasars/GRBs

CMB optical depth

Ly

-selected galaxies

Furlanetto, Oh, & Briggs (2006)



Ly

Emitters and HII Regions

Total optical depth in

Ly

 transition:

GP

3x10

5 x

HI 

1

 z

7

 3 / 2



 Damping wings are strong

IGM HI

x

H

=0

LAEs During Reionization x

H

=0.26

x

H

=0.51

x

H

=0.77

Mesinger & Furlanetto (2007)

 z=9, R=125 observation, with M>1.7x10

10 Msun

Galaxies in small bubbles (underdense regions) masked out by absorption

A Declining Number Density?

 Largest survey to date with Subaru

 Apparent decline at bright end

 Disputed by Dawson et al. (2007)

Kashikawa et al. (2006)

A Declining Number Density?

 Similar behavior to z=7

 One (!) detection

 L>10 43 erg/s detection threshold

Iye et al. (2006)

An Increasing Number Density?

 Stark et al. (2007) found 6 candidate LAEs behind massive clusters

Search along lensing caustics z=9-10

L~10 41 -10 42 erg/s

Most obvious interlopers ruled out

Stark et al. (2007), z=9

Kashikawa et al. (2006)

An Increasing Number Density?

Solid curves show mass functions with absorption

Four scenarios for luminosities

(right to left):

Same as z=6 LAEs

Same as z=6 LAEs, but Pop III

All baryons form Pop II stars, simultaneously

All baryons form Pop III stars, simultaneously

Reasonable scenarios require fully ionized!

Mesinger & Furlanetto (2008)

LAE Clustering

During Reionization

Nearly randomly distributed galaxy population

Small bubble: too much extinction, disappears

Large bubble: galaxies visible to survey

LAE Clustering

During Reionization

Small bubble: too much extinction, disappears

Large bubble: galaxies visible to survey

Absorption selects large bubbles, which tend to surround clumps of galaxies

LAE Clustering

During Reionization

Small bubble: too much extinction, disappears

Large bubble: galaxies visible to survey

Absorption selects large bubbles, which tend to surround clumps of galaxies

Enhanced Clustering

During Reionization

 Shows enhanced probability to have

N>1 galaxies in an occupied cell

 Measuring requires deep survey over

~10 6 -10 7 Mpc 3

Mesinger & Furlanetto (2008)

The Future of LAE Surveys

 Advantages:

 Familiar strategies

 Study galaxies as well

 Disadvantages:

 Uncertainties about galaxy formation

 Need large volume, deep surveys

 Indirect information about IGM

The Spin-Flip Transition

Proton and electron both have spin  magnetic fields

Produces 21 cm radiation

( n

=1420 MHz)

Extremely weak transition

 Mean lifetime ~10 7 yr

 Optical depth ~1% in fully neutral IGM



The 21 cm Transition

 Map emission (or absorption) from IGM gas

Requires no background sources

Spectral line: measure entire history

Direct measurement of

IGM properties

No saturation!

T b

23 x

HI

(1

 

)



1

 z

10

 1/ 2







T

S

T bkgd

T

S







H ( z ) /(1

 z )

 v r

/

 r





mK

SF, AS, LH (2004)

The Spin Temperature

CMB photons drive toward invisibility:

T

S

=T

CMB

Collisions couple T

S

 to T

K

Dominated by electron exchange in H-H collisions in neutral medium (Zygelman 2005)

 Dominated by H-e collisions in partially ionized medium (Furlanetto & Furlanetto

2006), with some contribution from H-p collisions (Furlanetto & Furlanetto 2007)

The Global Signal:

The Dark Ages

 Straightforward physics

 Expanding gas

 Recombination

 Compton scattering

SF, PO, FB (2006)

1

S

1/2

0

S

1/2

The Wouthuysen-Field

Mechanism I

Selection Rules:

D F=0,1 (except F=0  F=0)

2

P

3/2

1

P

3/2

1

P

1/2

0

P

1/2

Mechanism is effective with

~0.1 Ly

 photon/baryon

The Wouthuysen-Field

Mechanism II

Ly

 Ly

Ly

Ly

 Relevant photons are continuum photons that redshift into the Ly

 resonance

The Global Signal:

First Light

 First stars (quasars?) flood Universe with photons

 W-F effect

 Trigger absorption in cold IGM feedback

Pop III Stars

Pop II Stars

SF (2006)

The First Sources of Light:

X-ray Heating

X-rays are highly penetrating in IGM

Mean free path >Mpc

 Deposit energy as heat, ionization

Produced by…

Supernovae

Stellar mass black holes

Quasars

Very massive stars

The Global Signal:

First Light

 First stars (quasars?) flood Universe with photons

 W-F effect

 Heating

 Ionization

 Timing depends on f

*

, f esc

, f

X

, stellar population feedback

Pop III Stars

Pop II Stars

SF (2006)

21 cm Observations

 Experiments

 Global Signal: CoRE-

ATNF, EDGES

 Fluctuations: 21CMA,

LOFAR, MWA, GMRT,

PAPER, SKA

 Imaging: SKA

MWA

Terrestrial Interference

Mileura spectrum, 15 sec integrations

Two types:

Fixed site (low frequency filling factor)

Aircraft/meteor trail reflections (low duty cycle)

Basic strategy: excise contaminated channels

Bowman et al. (2007)

Ionospheric Distortions

Refraction in ionosphere distorts wavefronts

Analog of optical seeing layer

Solved on software level with calibration sources

Challenge: wide-field imaging

W. Cotton

Astronomical Foregrounds

Map at 150 MHz

 Contours are in Kelvin

Landecker et al. (1969)

The Synchrotron Foregrounds

 A single synchrotron electron produces a broad but smooth spectrum

B

Intensity

Frequency e path

The Synchrotron Foregrounds

 A single synchrotron electron produces a broad but smooth spectrum

Intensity

 Electron velocity scales the spectrum

Frequency

The Synchrotron Foregrounds

 Synchrotron spectrum mirrors distribution of

Intensity fast electrons

 Typically near powerlaw, with ~K/MHz gradient

Frequency

Measuring the Global Signal?

Signal gradient is few mK/MHz

Foregrounds vary as

(near) power law

Synchrotron, free-free

Gradient is few K/MHz

CoRE-ATNF, EDGES experiments are trying

Distinctive shape may help

SF (2006)

Foregrounds on Small Scales

0.5 MHz

Foreground Removal

Total Signal ~ 400 K

 Removal algorithms fairly well-developed

Zaldarriaga et al.

(2004), Morales &

Hewitt (2004), Santos et al. (2005),

McQuinn et al. (2007)

T b

Cleaned Signal ~ 10 mK

Frequency

Foreground Noise

 Thermal noise is NOT smooth: varies between each channel

 For first generation instruments, 1000 hr observations still have S/N<1 per pixel

 Imaging is not possible until SKA!

The Murchison Widefield Array

 Low Frequency

Demonstrator under construction (fully funded, first light

~2008)

Bowman et al. (2007)

 Located on sheep ranch in Western

Australia

The Murchison Widefield Array

Bowman et al. (2007)

 Bowtie antennae grouped in tiles of 16

Broad frequency response

Large field of view

Murchison Widefield Array:

Low Frequency Demonstrator

 Instrument characteristics

Radio-quiet site

500 16-element antennae in

1.5 km distribution

7000 m 2 total collecting area

Full cross-correlation of all 500 antennae

80-300 MHz

32 MHz instantaneous bandwidth at 8 kHz resolution

20-30 degree field of view Bowman et al. (2007)

Error Estimates: z=8

MWA

Foreground limit

(Mpc -1 )

SKA

Survey parameters

 z=8

T sys

=440 K t int

=1000 hr

B=6 MHz

No systematics!

MWA (solid black)

A eff

=7000 m 2

1.5 km core

SKA (dotted blue)

A eff

=1 km 2

5 km core

LOFAR very close to MWA

Error Estimates: z=12

Foreground limit

MWA

SKA

Survey parameters

 z=12

T sys

=1000 K t int

=1000 hr

B=6 MHz

No systematics!

MWA (solid black)

A eff

=9000 m 2

1.5 km core

SKA (dotted blue)

A eff

=1 km 2

5 km core

(Mpc -1 )

That’s a whole lotta trouble…

So what good is it, really?

The Global Signal

 Four Phases

 Dark Ages

 First Stars

 First Black Holes

 Reionization

Reionization BHs Stars Dark

Ages

SF (2006)

Ly

Fluctuations

 Ly

 photons decrease T

S near sources (Barkana &

Loeb 2004)

 Clustering

 1/r 2 flux

 Strong absorption near dense gas, weak absorption in voids

Cold, Absorbing

Cold, invisible

Ly

Fluctuations

Ly

 photons decrease T

S sources near

Clustering

1/r 2 flux

Strong absorption near dense gas, weak absorption in voids

Eventually saturates when IGM coupled everywhere

Cold, Absorbing

The Pre-Reionization Era

Net

X-ray

Ly

Pritchard & Furlanetto (2007)

Thick lines: Pop II model, z r

=7

Thin lines: Pop III model, z r

=7

Dashed: Ly

 fluctuations

Dotted: Heating fluctuations

Solid: Net signal

X-ray Fluctuations

 X-ray photons increase T

K near sources (Pritchard &

Furlanetto 2007)

 Clustering

 1/r 2 flux

 Hot IGM near dense gas, cool IGM near voids

Hot

Cool

+

X-ray and Ly

Fluctuations

=

Hot, emitting

Invisible

The Pre-Reionization Era

Net

X-ray

Ly

Pritchard & Furlanetto (2007)

Thick lines: Pop II model, z r

=7

Thin lines: Pop III model, z r

=7

Dashed: Ly

 fluctuations

Dotted: Heating fluctuations

Solid: Net signal

+

X-ray Fluctuations

=

Hot, emitting

Cold, absorbing

The Pre-Reionization Era

Net

X-ray

Ly

Pritchard & Furlanetto (2007)

Thick lines: Pop II model, z r

=7

Thin lines: Pop III model, z r

=7

Dashed: Ly

 fluctuations

Dotted: Heating fluctuations

Solid: Net signal

+

X-ray Fluctuations

=

Hot, emitting

The Pre-Reionization Era

Net

X-ray

Ly

Pritchard & Furlanetto (2007)

Thick lines: Pop II model, z r

=7

Thin lines: Pop III model, z r

=7

Dashed: Ly

 fluctuations

Dotted: Heating fluctuations

Solid: Net signal

21 cm Observations:

Reionization

100 Mpc comoving

Mesinger & Furlanetto

Reionization “Simulations”

100 Mpc comoving

 Implement in numerical simulation boxes

 Step 1: Generate initial conditions

 Step 2: Identify galaxies

Mesinger & Furlanetto

Biased Galaxy Formation:

Peaks and Patches

 Galaxies form at peaks in the density field

 Threshold decreases with time

 More galaxies

 Bigger galaxies

Identifying Galaxies

Filter density field to find peaks

Use excursion-set barrier to find masses

Adjust locations using

Zeldovich approximation

Similar to “peak-patch” method (Bond & Myers

1996), PINOCCHIO,

PTHALOS

Mesinger & Furlanetto (2007)

Identifying Galaxies

 Excellent statistical agreement

 Large-scale structure

 Poisson noise

 Accurate one-to-one for large galaxies

(Bond & Myers 1996)

Mesinger & Furlanetto (2007)

Reionization “Simulations”

100 Mpc comoving

 Implement in numerical simulation boxes

 Step 1: Generate initial conditions

 Step 2: Identify galaxies

Mesinger & Furlanetto

Photon Counting

 Assume galaxies have fixed ionizing efficiency

 Isolated galaxies generate HII regions

 Clustered galaxies work together

Galaxy

Ionized IGM

Neutral IGM

Photon Counting

 Assume galaxies have fixed ionizing efficiency

 Isolated galaxies generate HII regions

 Clustered galaxies work together

Reionization “Simulations” z=9.75, x i

=0.2

Implement in numerical simulation boxes

Step 1: Generate initial conditions

Step 2: Identify galaxies

Step 3: Paint on bubbles, working from outside in

100 Mpc comoving

Mesinger & Furlanetto

Reionization “Simulations” z=8.75, x i

=0.4

Implement in numerical simulation boxes

Step 1: Generate initial conditions

Step 2: Identify galaxies

Step 3: Paint on bubbles, working from outside in

100 Mpc comoving

Mesinger & Furlanetto

Reionization “Simulations” z=8, x i

=0.6

Implement in numerical simulation boxes

Step 1: Generate initial conditions

Step 2: Identify galaxies

Step 3: Paint on bubbles, working from outside in

100 Mpc comoving

Mesinger & Furlanetto

Reionization “Simulations” z=7.25, x i

=0.8

Implement in numerical simulation boxes

Step 1: Generate initial conditions

Step 2: Identify galaxies

Step 3: Paint on bubbles, working from outside in

Five hours on desktop!

100 Mpc comoving

Mesinger & Furlanetto

Success!

Filter A on halos Filter B on halos from N-body simulation from N-body simulation

Radiative

Transfer

Simulation

Excellent match for large scale features

Map details depend on filtering algorithm

Zahn et al. (2007), Mesinger & Furlanetto (2007)

The 21 cm Power Spectrum

MWA

SKA

MWA

SKA

(Mpc -1 )

Mesinger & Furlanetto (2007)

21 cm-Galaxy

Cross-Correlation z=8, x i

=0.6

Mesinger & Furlanetto

21 cm-Galaxy

Cross-Correlation

 Key advantages

 Unambiguous confirmation of cosmological signal

 Vastly reduces difficulty of foreground cleaning

 Only emission from sources in survey slice contributes

 Increase sensitivity and dynamic range

Helps with angular structure

 Science!

The 21 cm-Galaxy

Cross-Correlation

Can be done with LAEs or

LBGs

Significant advantages in 21 cm data analysis (SF & AL

2007)

Challenge: wide-field near-IR surveys

JWST?

JDEM?

Ground-based cameras?

Lidz, Zahn, & Furlanetto (in prep)

Conclusions

LAE searches beginning to pay off

Strange star formation?

Robust signatures will be in clustering

The 21 cm transition offers great possibilities

Pre-reionization: properties of first sources, cosmology

Reionization: morphology and growth of bubbles

Experimental challenges still large

Good synergy with other probes of high-z universe!

 Cross-correlation, Ly

 searches, quasars…

See our Physics Reports review (Furlanetto,

Oh, & Briggs 2006, astro-ph/0608032) for more information on 21 cm possibilities!

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