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Barkana

21-cm cosmology uses observations of neutral hydrogen during the cosmic dark ages and epoch of reionization to probe fundamental cosmology and astrophysics. It has the potential to map out density fluctuations from z=20-200 and observe the first galaxies and cosmic reionization through 21-cm power spectra with an array of radio interferometers. Key challenges include removing astrophysical and terrestrial foreground signals to detect the tiny cosmological 21-cm signal.

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Anoop Sahal
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47 views22 pages

Barkana

21-cm cosmology uses observations of neutral hydrogen during the cosmic dark ages and epoch of reionization to probe fundamental cosmology and astrophysics. It has the potential to map out density fluctuations from z=20-200 and observe the first galaxies and cosmic reionization through 21-cm power spectra with an array of radio interferometers. Key challenges include removing astrophysical and terrestrial foreground signals to detect the tiny cosmological 21-cm signal.

Uploaded by

Anoop Sahal
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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21-cm Cosmology

Rennan Barkana ‫רנן ברקנא‬


Cosmic History

Atomic
Hydrogen

RB 2006, Science Review


CMB: 2D temperature map, 10-5 fluctuations

COBE
1992

The Nobel Prize


in Physics 2006

John C. Mather George F. Smoot


CMB: 2D temperature map, 10-5 fluctuations

COBE
1992

WMAP
2003
Lyα Spectra:

E n

Resonance Line +
Cosmological Redshift

1100A  (1 + z)
Lyα Spectra: 1D density distribution

E n

Resonance Line +
Cosmological Redshift

1100A  (1 + z)

= 1216A  (1 + z )
21-cm Spectra

p e p e

Resonance Line +
Cosmological Redshift
Diffuse Source: The CMB

The observable
universe

The CMB h  kBT


An observer
Edge of the I  = 2kBT  2/c2
observable
universe
Redshift Slices of the Universe
Cosmic History

Atomic
Hydrogen

Naoz, Noter & RB 2006

RB 2006, Science Review


The Spin Temperature

p e p e

= 21 cm
 = 1420 MHz
E = 5.9  10 6 eV
E
k B = T  = 0.068 K

n1
è Té
n0 = 3 exp  T S
What determines TS?

TS → T
CMB

TS → Tk

n=2
TS → Tk
Lyα

Wouthuysen 1952 n=1


Field 1958
Mean Temperatures
T

TS

Tk
Mean Temperatures
T

TS TS

Tk

+ Ly

Madau, Meiksin
& Rees 1997
Chen &
Miralda-Escude 2004
Foregrounds => 21cm Fluctuations
21cm Power Spectrum
 ∝ nH T S = f(T k , Ly)
Fundamental Cosmology: Linear
(Primordial fluctuations, Inflation, Cosmological parameters)
=> Density (ρ), Temperature (ρ + CMB)
Astrophysics: Non-linear
(Galaxy formation, Star formation, Black holes)
=> Radiation: Temperature, Ionization, Lyα

Anisotropy:  = cos  RB & Loeb 2005



k
4P (k) + 22P iso(k) + P iso(k)
21cm Power Spectra
Naoz & RB 2005

z = 200
z = 150
z = 100
z = 50
z = 35
z = 25
z = 20

Loeb &
Zaldarriaga 2004:
CMB: ~107
21-cm: ~1016
21-cm fluctuations from Lyα

z = 20
Density Many small galaxies
fluctuations

A few large galaxies

Poisson
fluctuations

RB & Loeb 2005


Naoz & RB 2007
Cosmic Reionization

100/h Mpc = 0.5°


RB & Loeb 2004 Mellema et al. 2006
21-cm Power Spectrum

MWA, LOFAR

Zahn et al. 2006


simulation

RB 2007
Foregrounds

RFI: Radio Frequency Interference

Ionosphere: Scintillation
80  200 km

Galactic Synchrotron Emission 408 MHz


−2.6
 ν 
Tsky ~ 180   K Cygnus A
 180 MHz 
Extragalactic Radio Sources
Experiments
tint ~ 100 hr, ∆ν ~1MHz ⇒ 1mK
∆θ ~10′
21CMA: 21 Centimeter Array

China ~ 10,000 Antenna Interferometer

MWA: The Mileura Wide-field Array

Australia, MIT, Harvard

LOFAR: The Low Frequency Array

Holland + Europe

SKA: The Square Kilometer Array


Summary:

• 21-cm cosmology: The next great


cosmological probe
• Probe:
– Primordial Density Fluctuations (z=20-200)
– The First Galaxies (z=65; Lyα radiation: z=20)
– Cosmic Reionization

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