Probing the High-z Universe with Galaxy Counts from Ultra Deep Surveys and the Cosmic Near Infrared Background

1
Probing the High-z Universe with Galaxy Counts
from Ultra Deep Surveys and the Cosmic Near
Infrared Background

• Eiichiro Komatsu (Univ. of Texas, Austin)
• Astrophysics Seminar_at_UCSB
• May 23, 2007

• References
• Elizabeth Fernandez EK, ApJ, 646, 703 (2006)
• Elizabeth Fernandez EK, to be submitted

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What Do I Mean By High-z?

• I mean zgt6.
• An interesting epoch in the cosmic history
  reionization of the universe
• Direct detections of galaxies at zgt6 are now
  possible.
• eg., Ly? emitter at z6.96 discovered in the
  Subaru Deep Field (Iye et al. 2006)

3
Going Further

• JWST will peer deeper into the high-z
  universeafter 2013.
• Can we do anything interesting now, and help
  define science goals of JWST better?
• Two topics in this talk along this direction
• The Cosmic Near Infrared Background
• Ly??emitters at zgt6
• One more topic if time permits
• 21-cm fluctuations vs the Cosmic Microwave
  Background (Alvarez, EK, Dore Shapiro 2006)

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Why Study Cosmic Near Infrared Background? (1-4um)

• New window into 7ltzlt30 (e.g., Redshifted Ly?)
• Can we detect photons from early generation stars
  and their nebulae? What can we learn from these
  photons?
• The presence of the signal is guaranteed, but the
  amplitude of the signal is not known.
• Measurement of these photons is challenging
  because of contaminations due to
• Zodiacal light, and
• Galaxies at zlt6.

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Near Infrared Background Current Data vs
Challenges

• Extra-galactic infrared background in J and K
  bands above zodiacal light 70 nW/m2/sr
• These Measurements have been challenged.
• Upper limits from blazar spectra lt14 nW/m2/sr
  (Aharonian et al. 2006)
• Incomplete subtraction of Zodiacal light? 15
  nW/m2/sr (Wright 2001) lt6 nW/m2/sr (Thompson et
  al. 2006)
• Lets be open-minded.
• Clearly, we need better data!
• Better data will come from a rocket experiment,
  CIBER (Bock et al), in 2008.

Observed NIRB
Excess?
Galaxy Contribution at zlt6
Matsumoto et al. (2005)
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Previous Study Metal-free Stars, or Mini-quasars?

• First stars?
• Very massive (1000 Msun), metal-free (Z0) stars
  can explain the excess signal.
• Santos, Bromm Kamionkowski (2002) Salvaterra
  Ferrara (2003)
• Mini quasars?
• Cooray Yoshida (2004) studied the contribution
  from mini-quasars.
• Madau Silk (2005) showed that it would
  over-produce soft X-ray background.

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Our Prediction Fernandez Komatsu (2006)

• We dont need metal-free stars!
• Dont be too quick to jump into conclusion that
  metal-free, first stars have been seen in the
  NIRB. (Kashlinsky et al. 2005, 2007)
• We dont need them (yet) to explain the data.
• Stars with metals (eg, Z1/50 solar) can produce
  nearly the same amount of excess light per star
  formation rate.
• This is not a negative result, but is actually a
  good news for NIRB we dont really expect a lot
  of metal-free stars to be around at z7-10.
• Why? A simple energy conservation.

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Simple, but Robust, Calculation
What we measure
Simple argument Luminosity per volume
(Stellar mass energy) x(Radiation
efficiency) /(Time during which radiation is
emitted)
Can be calculated
Unknown
Radiation Efficiency
IMF (Salpeter, Larson, Top-heavy)
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Stellar data from Schaller et al. (1992)
Schaerer (2002)
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Sample Initial Mass Functions of Stars
Salpeter
)
(
Larson
Top-heavy
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Rest-frame Spectrum of lt??gt
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NIRB Spectrum per SFR
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The Madau Plot at zgt7
You dont have to take this seriously for now. We
need better measurements!
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How About Metal Production?

• Is the inferred stat formation rate at zgt7
  consistent with the metal abundance in the
  universe?
• Did these early stars that are responsible for
  the near infrared background over-enrich the
  metals in the universe too early?

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Theoretical data for Z1/50 solar from
Portinari et al. (1998)
White dwarf or neutron star
Weak SN Black hole by fallback
Direct collapse to black hole
Type II SN
Pulsational Pair Instability SN
Pair Instability SN
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Metal Production (Z1/50 solar)
The metal density now is 1.2 108 M8 Mpc-3 -gt
The upper limit from the near infrared background
for a larson IMF is excluded, but most of the
parameter space survives the metallicity
constraint.
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A Comment on Madau Silk (2005)

• They claim that the stellar mass density required
  to explain the excess near infrared background is
  at least 2 of the baryon density in the
  universe.
• this is energetically and astrophysically
  daunting (Madau Silk 2005)
• It would be daunting if, and only if, these
  baryons had remained locked up in the stars and
  their remnants however,
• Baryons should be recycled!! If all the baryons
  were recycled (other extreme case), 2 should be
  divided by the number of generations of star
  formation, which is of order 10. So, the actual
  number should be somewhere between 2 and 0.1,
  which is not daunting at all.

18
Smoking-gun Anisotropy

• Press-release from Kashlinsky et al.
• Detection of significant anisotropy in the
  Spitzer IRAC data
• They claim that the detected anisotropy
  originates from the first stars.
• Their claim has been challenged by Cooray et al.
• We need better data from CIBER, which is designed
  to measure anisotropy over 2 deg2
• The Spitzer image (left) is over 12x6.

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The Future is in Anisotropy

• Previous model (Kashlinsky et al. 2005 Cooray et
  al. 2006) ignored ionized bubbles.
• May not be accurate enough to interpret the data
  from CIBER.
• We will use the reionization simulation (Iliev et
  al. 2006) to make simulated maps of the NIRB
  anisotropy coming soon!

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What Are the Sources of the Near Infrared
Background?

• One candidate Lyman-alpha emitting galaxies at
  zgt7.
• What do we learn about them from the existing
  Lyman-alpha Emitter (LAE) searches?
• Subaru Deep Field
• 34 LAEs at z5.7 (Shimasaku et al. 2006)
• 17 LAEs at z6.5 (Taniguchi et al. 2005
  Kashikawa et al. 2006)
• 1 LAE at z7 (Iye et al. 2006)
• LALA Survey
• 1 LAE at z6.5 (Rhoads et al. 2004)
• ISAAC/VLT
• No detection at z8.8 (Willis et al. 2006 Cuby
  et al. 2007)

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Very Simple Model of Luminosity Function

• Simply count the number of halos above a certain
  mass Cumulative Mass Function
• Mass is related to luminosity by a mass-to-light
  ratio M/L (M is the total mass.)
• We just stretch the cumulative mass function
  horizontally by rescaling the mass with M/L.
• One parameter fit!

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Cumulative Mass Function (Sheth-Tormen Mass
Function)
If we stretch the horizontal axis by M/L, then we
get
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Luminosity Function of LAEs (1) SDF at z5.7
M/Lband95-120
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Luminosity Function of LAEs (2) SDF at z6.5
M/Lband85-100
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Luminosity Function of LAEs (3) SDF at z7 (from
1 LAE)
M/Lband100
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Luminosity Function of LAEs (4)VLT/ISAAC at
z8.8 (no detection)
M/Lbandgt7
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Mass-to-observed light Ratio to
Mass-to-bolometric light Ratio

• The luminosity of LAEs estimated from a given
  survey is not the actual luminosity of the
  source.
• Its a luminosity integrated over instruments
  bandwidth.
• Its a luminosity after absorption and
  extinction.
• Conversion

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Getting Lbol/Lband From Model Spectrum

• A sample spectrum for a galaxy of Z1/50 solar
  with a Salpeter IMF. The intrinsic equivalent
  width of Lyman-alpha 483 angstroms.

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Lband/Lbol How Much Light Are We Losing?

• Lower metallicity -gt Larger Lyman-alpha
• We dont lose much light -gt less correction
  necessary.
• Hence, larger Lband/Lbol.
• Very insensitive to the IMF

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Main Result Inferred (M/Lbol)/?esc

• (M/Lbol)/?esc is remarkably stable from z5.7 to
  7!
• No detection of sources at z8.8 is consistent
  with the expectation.
• We see no evidence for the evolution of
  (M/Lbol)/?esc from z5.7 to 8.8.

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What Do Our Results Imply?

• LAEs are normal galaxies, if
• M/Lbol10, if a good fraction of Lyman-alpha
  photons survived, ?esc0.5.
• The predicted EW is consistent with observation,
  EW50-300 angstroms, if the metallicity is
  normal Z1/50-1 solar.
• LAEs are starbursts, if
• M/Lbol1, if ?esc0.05-0.1.
• The predicted EW is consistent with observation,
  if the metallicity is low Z0-1/50 solar.

• No evidence for the end of reionization!
• No evidence for the evolution of ?esc, unless
  ?esc goes down and M/Lbol goes up by the same
  amount to keep (M/Lbol)/?esc constant.

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You can make it more complex.

• Why not stretching it vertically as well?
• Duty cycle, ?. (Haiman Spaans 1999 Dijkstra,
  Wyithe Haiman 2006).
• In our model, ????
• Why assuming a deterministic L-M relation?
• P(LM) Probability for a halo of mass M to host
  a galaxy of luminosity, L. (e.g., Cooray
  Milosavljevic 2005)
• In our model, P(LM)deltaM-(M/L)L.
• The data are not good enough to constrain more
  parameters necessary to characterize these
  properties.
• Our simpler model does yield reasonable results.

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A Comment on SalvaterraFerrara (2006)

• They claim that the excess near infrared
  background cannot originate from high-z galaxies,
  because such galaxies are not seen in high-z
  galaxy surveys.
• They show that the excess NIRB requires hundreds
  of galaxies to be detected in e.g., VLT/ISAAC
  field, where none was found.
• Their model galaxy is extremely bright
  M/L0.001.
• But, we dont need such a population!
• NIRB measures the TOTAL energy.
• Galaxies can release the same amount of energy by
• an intense starbust for a few million years
  (M/L0.001),
• a moderate burst for a few hundred million years
  (M/L0.1-1), or
• a normal star formation (M/L10).
• SF(2006) ruled out only the first possibility.

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Reionization CMB - 21cm correlationAlvarez,
Komatsu, Dore Shapiro 2006, ApJ, 647, 840
21-cm maps result from line-emission
Doppler is a projected effect on CMB

• Doppler effect comes from peculiar velocity along
  l.o.s.
• 21-cm fluctuations due to density and ionized
  fraction
• We focus on degree angular scales

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21cm x CMB Doppler

• 21cm lines
• Produced by neutral hydrogen during reionization
• As reionization proceeds, 21cm slowly dissappears
  morphology of reionization imprinted on 21cm
  anisotropy
• Because it is line emission, redshift ? frequency
• CMB Doppler effect
• Free electrons during reionization scatter CMB
  photons
• Electrons moving towards us ? blueshift ? hot
  spot
• Electrons moving away from us ? redshift ? cold
  spot
• Doppler effect is example of secondary
  anisotropy in CMB
• Both effects are sensitive to reionization
• The cross-correlation is cleaner!
• In analogy to TE correlation of CMB, their cross
  correlation is more immune to systematics because
  errors are uncorrelated between the two
  observations

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The Effect is Easy to Understand

• Reionization ? positive correlation
• Recombination ? negative correlation

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21cm Anisotropy

• To get cross-correlation between 21cm and
  Doppler, we need expression for spherical
  harmonic coefficients alm

• To leading order, the anisotropy is dependent on
  fluctuations in density and ionized fraction

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Doppler Anisotropy

• Doppler arises from integral of velocity along
  line of sight

• Continuity equation ? velocity fluctuation
  proportional to density fluctuation

• We ignore fluctuations of density
  (Ostriker-Vishniac effect) and ionized fraction
  since they are higher order effects

• To leading order, the Doppler anisotropy is
  dependent on fluctuations of velocity ? density

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Cross-correlation

• Given the coefficients alm for 21cm and Doppler,
  the cross-correlation can be found using

• Shape of angular correlation same as linear power
  spectrum ClP(kl/r)
• Evolution of the peak correlation amplitude
• (at l100) with redshift ? reionization history

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Cross-correlation

• The shape of the correlation traces the linear
  matter power spectrum at large scales (l100)

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Probing Reionization History

• Cross-correlation peaks when ionized fraction
  about a half
• Sign and amplitude of correlation constrains
  derivative of ionized fraction
• Typical signal amplitude 500 (?K)2
• Above expected error from Square Kilometer Array
  for 1 year of observation 135 (?K)2

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Our Prediction for SKA

• The SKA data should be correlated with CMB, and
  WMAP data are good enough!
• It is even plausible that the first convincing
  evidence for 21-cm from reionization would come
  from the cross-correlation signal.
• Systematic errors, foregrounds, or unaccounted
  noise wont produce the cross-correlation, but
  will produce spurious signal in the
  auto-correlation.

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Summary

• There are various observational windows to the
  universe at zgt7 before JWST.
• Near infrared background
• Lyman-alpha emitters
• The current data of LAEs do not show evidence for
  the end of reionization up to z7.
• On-going follow-up, deeper surveys with Subaru at
  z7 and VLT at z8.8 are going to be very
  interesting!
• The excess near infrared background is likely
  caused by stars with metals.
• We dont need metal-free stars, which is a good
  news.
• Future lies in anisotropy a better prediction is
  required for the data from CIBER (launch in 2008)
• More ambitious future with 21-cm
• The 21-cm data should be correlated with CMB for
  a conclusive detection of the cosmic signal.