Title: Probing the High-z Universe with Galaxy Counts from Ultra Deep Surveys and the Cosmic Near Infrared Background
1Probing 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
2What 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)
3Going 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)
4Why 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.
5Near 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)
6Previous 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.
7Our 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.
8Simple, 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)
9Stellar data from Schaller et al. (1992)
Schaerer (2002)
10Sample Initial Mass Functions of Stars
Salpeter
)
(
Larson
Top-heavy
11Rest-frame Spectrum of lt??gt
12NIRB Spectrum per SFR
13The Madau Plot at zgt7
You dont have to take this seriously for now. We
need better measurements!
14How 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?
15Theoretical 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
16Metal 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.
17A 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.
18Smoking-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.
19The 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!
20What 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)
21Very 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!
22Cumulative Mass Function (Sheth-Tormen Mass
Function)
If we stretch the horizontal axis by M/L, then we
get
23Luminosity Function of LAEs (1) SDF at z5.7
M/Lband95-120
24Luminosity Function of LAEs (2) SDF at z6.5
M/Lband85-100
25Luminosity Function of LAEs (3) SDF at z7 (from
1 LAE)
M/Lband100
26Luminosity Function of LAEs (4)VLT/ISAAC at
z8.8 (no detection)
M/Lbandgt7
27Mass-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
28Getting 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.
29(No Transcript)
30Lband/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
31Main 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.
32What 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.
33You 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.
34A 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.
35Reionization 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
3621cm 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
37The Effect is Easy to Understand
- Reionization ? positive correlation
- Recombination ? negative correlation
3821cm 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
39Doppler 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
40Cross-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
41Cross-correlation
- The shape of the correlation traces the linear
matter power spectrum at large scales (l100)
42Probing 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
43Our 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.
44Summary
- 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.