Observing the First Galaxies and the Reionization Epoch Steve Furlanetto UCLA

advertisement
Observing the First Galaxies
and the Reionization Epoch
Steve Furlanetto
UCLA
February 5, 2008
Outline


Introduction: Observing Reionization
Galaxy Surveys



The 21 cm Transition as a Cosmological Probe






Current observations of LAEs
The Clustering Signature
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
Dark Ages
First
Galaxies



Reionization
Galaxies,
Clusters,
etc.
G. Djorgovski

Last scattering:
z=1089, t=379,000 yr
Today: z=0, t=13.7
Gyr
Reionization: z=6-20,
t=0.2-1 Gyr
First galaxies: ?
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:
3/2
1 z 
5
 GP  3x10 x HI

 7 

Damping wings are
strong
IGM HI
LAEs During Reionization
xH=0
xH=0.26
xH=0.51
xH=0.77
Mesinger & Furlanetto (2007)


z=9, R=125 observation, with M>1.7x1010 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>1043 erg/s
detection threshold
Iye et al. (2006)
An Increasing Number Density?

Stark et al. (2007) found 6
candidate LAEs behind
massive clusters




Stark et al. (2007), z=9
Search along lensing caustics
z=9-10
L~1041-1042 erg/s
Most obvious interlopers ruled
out
Kashikawa et al. (2006)
An Increasing Number Density?


Solid curves show mass
functions with absorption
Four scenarios for luminosities
(right to left):





Mesinger & Furlanetto (2008)
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!
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


Mesinger & Furlanetto (2008)
Shows enhanced
probability to have
N>1 galaxies in an
occupied cell
Measuring requires
deep survey over
~106-107 Mpc3
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 ~107 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!
1 z 1/ 2 TS  Tbkgd H(z) /(1 z) 
Tb  23x HI (1 ) 
 

mK
 10   TS
 v r /r 
SF, AS, LH (2004)
The Spin Temperature


CMB photons drive toward invisibility:
TS=TCMB
Collisions couple TS to TK


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



SF, PO, FB (2006)
Expanding gas
Recombination
Compton scattering
The Wouthuysen-Field
Mechanism I
Selection Rules:
DF=0,1 (except F=0  F=0)
2P3/2
1P3/2
1P1/2
0P1/2
1S1/2
0S1/2
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*,
fesc, fX, stellar
population
feedback
Pop III Stars
Pop II Stars
SF (2006)
21 cm Observations

Experiments



Global Signal: CoREATNF, 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
Intensity
B
Frequency
e- path
The Synchrotron Foregrounds


A single synchrotron
electron produces a
broad but smooth
spectrum
Electron velocity
scales the spectrum
Intensity
Frequency
The Synchrotron Foregrounds


Synchrotron spectrum
Intensity
mirrors distribution of
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



CoRE-ATNF, EDGES
experiments are trying

SF (2006)
Synchrotron, free-free
Gradient is few K/MHz
Distinctive shape may help
Foregrounds on Small Scales
0.5 MHz
Foreground Removal

Removal algorithms
fairly well-developed
Zaldarriaga et al.
(2004), Morales &
Hewitt (2004), Santos
et al. (2005),
McQuinn et al. (2007)
Tb
Total Signal ~ 400 K
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


Bowman et al. (2007)
Low Frequency
Demonstrator under
construction (fully
funded, first light
~2008)
Located on sheep
ranch in Western
Australia
The Murchison Widefield Array

Bowtie antennae grouped
in tiles of 16


Bowman et al. (2007)
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 m2 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

Survey parameters

MWA





SKA
MWA (solid black)



Foreground
limit


Aeff=7000 m2
1.5 km core
SKA (dotted blue)

(Mpc-1)
z=8
Tsys=440 K
tint=1000 hr
B=6 MHz
No systematics!
Aeff=1 km2
5 km core
LOFAR very close to MWA
Error Estimates: z=12

Survey parameters

MWA





SKA
MWA (solid black)



Foreground
limit
Aeff=9000 m2
1.5 km core
SKA (dotted blue)


(Mpc-1)
z=12
Tsys=1000 K
tint=1000 hr
B=6 MHz
No systematics!
Aeff=1 km2
5 km core
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 TS near
sources (Barkana &
Loeb 2004)



Clustering
1/r2 flux
Cold, Absorbing
Strong absorption
near dense gas, weak
absorption in voids
Cold, invisible
Ly Fluctuations

Ly photons decrease TS near
sources




Clustering
1/r2 flux
Strong absorption near dense
gas, weak absorption in voids
Eventually saturates when IGM
coupled everywhere
Cold, Absorbing
The Pre-Reionization Era

X-ray
Net
Ly




Pritchard & Furlanetto (2007)
Thick lines: Pop II
model, zr=7
Thin lines: Pop III
model, zr=7
Dashed: Ly
fluctuations
Dotted: Heating
fluctuations
Solid: Net signal
X-ray Fluctuations

X-ray photons
increase TK near
sources (Pritchard &
Furlanetto 2007)



Clustering
1/r2 flux
Hot IGM near dense
gas, cool IGM near
voids
Hot
Cool
X-ray and Ly Fluctuations
Hot, emitting
+
=
Invisible
The Pre-Reionization Era

X-ray
Net
Ly




Pritchard & Furlanetto (2007)
Thick lines: Pop II
model, zr=7
Thin lines: Pop III
model, zr=7
Dashed: Ly
fluctuations
Dotted: Heating
fluctuations
Solid: Net signal
X-ray Fluctuations
Hot, emitting
+
=
Cold, absorbing
The Pre-Reionization Era

X-ray
Net
Ly




Pritchard & Furlanetto (2007)
Thick lines: Pop II
model, zr=7
Thin lines: Pop III
model, zr=7
Dashed: Ly
fluctuations
Dotted: Heating
fluctuations
Solid: Net signal
X-ray Fluctuations
+
=
Hot, emitting
The Pre-Reionization Era

X-ray
Net
Ly




Pritchard & Furlanetto (2007)
Thick lines: Pop II
model, zr=7
Thin lines: Pop III
model, zr=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




Mesinger & Furlanetto (2007)
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
Identifying Galaxies

Excellent statistical
agreement



Mesinger & Furlanetto (2007)
Large-scale structure
Poisson noise
Accurate one-to-one
for large galaxies
(Bond & Myers 1996)
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
Ionized IGM
Galaxy
Neutral IGM
Photon Counting



Assume galaxies
have fixed ionizing
efficiency
Isolated galaxies
generate HII regions
Clustered galaxies
work together
Reionization “Simulations”
z=9.75, xi=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, xi=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, xi=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, xi=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
from N-body
simulation
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, xi=0.6
Mesinger & Furlanetto
21 cm-Galaxy
Cross-Correlation

Key advantages


Unambiguous confirmation of cosmological signal
Vastly reduces difficulty of foreground cleaning


Increase sensitivity and dynamic range


Only emission from sources in survey slice contributes
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



Lidz, Zahn, & Furlanetto (in prep)
JWST?
JDEM?
Ground-based cameras?
Conclusions

LAE searches beginning to pay off



The 21 cm transition offers great possibilities




Strange star formation?
Robust signatures will be in clustering
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!
Download