Cosmology with the 21 cm Transition

1
Cosmology with the 21 cm Transition

• Steve Furlanetto
• Yale University
• September 25, 2006

2
Outline

• The 21 cm transition
• The Dark Ages
• First Light
• Reionization
• Measuring the Matter Power Spectrum
• Summary

See our Physics Reports review (Furlanetto, Oh,
Briggs 2006, astro-ph/0608032) for more
information!
3
The 21 cm Transition

• Map emission (or absorption) from IGM gas
• Dark Ages only probe!
• Spectral line measure entire history
• Direct measurement of IGM properties

SF, AS, LH (2004)
4
The Spin Temperature

• In the absence of coupling mechanisms, TSTCMB
• Collisions couple TS to TK
• Efficient when d gt 15 10/(1z)2 if relatively
  hot
• Dominated by electron exchange in H-H collisions
  in neutral medium (Zygelman 2005), or H-e-
  collisions in partially ionized medium
  (Furlanetto Furlanetto 2006)
• The Wouthuysen-Field Effect
• Pump triplet state with absorption/re-emission of
  Ly? photons
• Becomes effective when 0.1 Ly? photon/baryon

5
Observing the Signal

• The Challenges
• Terrestrial radio frequency interference
• Ionospheric seeing
• Foregrounds
• Instrumental issues (polarization leakage,
  sidelobe control,)
• Noise so large, imaging extremely difficult!

LOFAR
6
Error Estimates z8

• Survey parameters
• z8
• Tsys440 K
• tint1000 hr
• B6 MHz
• No systematics!
• MWA (solid black)
• Aeff7000 m2
• 1.5 km core
• SKA (dotted blue)
• Aeff1 km2
• 5 km core

MWA
SKA
Foreground limit
after McQuinn et al. (2005)
7
Error Estimates z12

• Survey parameters
• z12
• Tsys1000 K
• tint1000 hr
• B6 MHz
• No systematics!
• MWA (solid black)
• Aeff9000 m2
• 1.5 km core
• SKA (dotted blue)
• Aeff1 km2
• 5 km core

MWA
SKA
Foreground limit
8
The Global SignalThe Dark Ages

• Straightforward physics
• Fluctuations directly trace matter power spectrum
  (Loeb Zaldarriaga 2004)
• 3D dataset
• Small-scale power

SF, PO, FB (2006)
9
The Dark Ages Dark Matter Decay
Dark matter decay models
?1016 yr
?1019 yr
Standard calculation
SF, PO, EP (2006)
10
The Global SignalFirst Light

• First stars (quasars?) flood Universe with
  photons
• Heating
• W-F effect
• Ionization
• Timing depends on f, fesc, fX, stellar population

feedback
weak X-rays
Pop II Stars
SF (2006)
11
The Ly? and Heating Eras

• Ly? photons create fluctuations around first
  sources (Barkana Loeb 2004, Pritchard
  Furlanetto 2006)
• X-rays seed fluctuations in TS (and hence ?Tb)
• Discrete (biased) sources and 1/r2 flux
• Soft X-rays have shorter mean free paths
• Rapid structure formation

Pritchard Furlanetto (2006)
12
21 cm Observations Reionization
z18.3
13 Mpc comoving
Dn0.1 MHz
SF, AS, LH (2004)
13
21 cm Observations Reionization
z16.1
13 Mpc comoving
Dn0.1 MHz
SF, AS, LH (2004)
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21 cm Observations Reionization
z14.5
13 Mpc comoving
Dn0.1 MHz
SF, AS, LH (2004)
15
21 cm Observations Reionization
z13.2
13 Mpc comoving
Dn0.1 MHz
SF, AS, LH (2004)
16
21 cm Observations Reionization
z12.1
13 Mpc comoving
Dn0.1 MHz
SF, AS, LH (2004)
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21 cm Observations Reionization
z11.2
13 Mpc comoving
Dn0.1 MHz
SF, AS, LH (2004)
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21 cm Observations Reionization
z10.4
13 Mpc comoving
Dn0.1 MHz
SF, AS, LH (2004)
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21 cm Observations Reionization
z9.8
13 Mpc comoving
Dn0.1 MHz
SF, AS, LH (2004)
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21 cm Observations Reionization
z9.2
13 Mpc comoving
Dn0.1 MHz
SF, AS, LH (2004)
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21 cm Observations Reionization
z8.7
13 Mpc comoving
Dn0.1 MHz
SF, AS, LH (2004)
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21 cm Observations Reionization
z8.3
13 Mpc comoving
Dn0.1 MHz
SF, AS, LH (2004)
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21 cm Observations Reionization
z7.9
13 Mpc comoving
Dn0.1 MHz
SF, AS, LH (2004)
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21 cm Observations Reionization
z7.5
13 Mpc comoving
Dn0.1 MHz
SF, AS, LH (2004)
25
21 cm Observations Reionization
z9.2
13 Mpc comoving
Dn0.1 MHz
SF, AS, LH (2004)
26
The Power Spectrum

• Rich set of information from bubble distribution
• Timing growth of structure
• Underlying source population (SF, MM, LH 2005)
• Uniform ionizing component (SF, MZ, LH 2004b)
• Feedback (SF, MZ, LH 2004b)
• Correlation with density field (SF, MZ, LH 2004b)
• Also must consider higher-order statistics!

xi0.59
xi0.78
xi0.69
xi0.48
xi0.36
xi0.13
z10
27
Fundamental Cosmology?

• Probably a period where density dominates before
  reionization measure matter power spectrum
• Modest improvements to small scales (neutrinos,
  tilt, etc. McQuinn et al. 2005, Bowman et al.
  2005)
• Redshift space distortions
• Anisotropic can extract matter power spectrum
  (Bharadwaj Ali 2004, Barkana Loeb 2004)

SF (2006)
28
Anisotropic Power Spectrum Error Estimates at
z8

• Survey parameters
• z8
• Tsys440 K
• tint1000 hr
• B6 MHz
• No systematics!
• MWA (solid black)
• Aeff7000 m2
• 1.5 km core
• SKA (dotted blue)
• Aeff1 km2
• 5 km core

MWA
SKA
Foreground limit
after McQuinn et al. (2005)
29
Conclusions

• The 21 cm line is a unique probe of the
  high-redshift universe
• Reionization measures distribution of ionized
  gas and its relation to sources, at every
  redshift
• First Light measures the impact of these sources
  on their environment
• Dark Ages clean probe of cosmology and of
  exotic processes like dark matter decay

See our Physics Reports review (Furlanetto, Oh,
Briggs 2006, astro-ph/0608032) for more
information!