Probing the High-z Universe with Galaxy Counts from Ultra D

eep Surveys and the Cosmic Near Infrared Background

Eiichiro Komatsu (Univ. of Texas, Austin)Astrophysics Seminar@UCSBMay 23, 2007

ReferencesElizabeth Fernandez & EK, ApJ, 646, 703 (2006)Elizabeth Fernandez & EK, to be submitted

What Do I Mean By “High-z”? I mean z>6. An interesting epoch i

n the cosmic history: reionization of the universe

Direct detections of galaxies at z>6 are now possible. eg., Ly emitter at z=

6.96 discovered in the Subaru Deep Field (Iye et al. 2006)

Going Further… JWST will peer deeper into the high-z universe

…after 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 Lyemitters at z>6

One more topic if time permits: 21-cm fluctuations vs the Cosmic Microwave Back

ground (Alvarez, EK, Dore & Shapiro 2006)

Why Study Cosmic Near Infrared Background? (1-4um) New window into 7<z<30 (e.g., Redshifted Ly) Can we detect photons from early generation stars and th

eir 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 z<6.

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: <14

nW/m2/sr (Aharonian et al. 2006) Incomplete subtraction of Zodiacal ligh

t? ~15 nW/m2/sr (Wright 2001); <6 nW/m2/sr (Thompson et al. 2006)

Let’s be open-minded. Clearly, we need better data! Better data will come from a rocket

experiment, CIBER (Bock et al), in 2008.

Excess?

Galaxy Contribution at z<6

Observed NIRB

Matsumoto et al. (2005)

Previous Study: Metal-free Stars, or Mini-quasars?

First stars? Very massive (~1000 Msun), metal-free (Z=

0) stars can explain the excess signal. Santos, Bromm & Kamionkowski (2002); S

alvaterra & 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.

Our Prediction: Fernandez & Komatsu (2006) We don’t need metal-free stars!

Don’t be too quick to jump into conclusion that metal-free, first stars have been seen in the NIRB. (Kashlinsky et al. 2005, 2007)

We don’t need them (yet) to explain the data. Stars with metals (eg, Z=1/50 solar) can prod

uce 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 don’t really expect a lot of metal-free stars to be around at z~7-10.

Why? A simple energy conservation.

Simple, but Robust, Calculation

Unknown Can be calculated

What we measure

€

p(υ ,z)

= (M*c2) /Time × Efficiency

= ˙ ρ *(z)c 2 ∑α

eυα€

Iυ =c

4π

p([1+ z]υ ,z)dz

H(z)(1+ z)∫

€

eυα ≡

1

m*

dm mf (m)L υ

α (m)τ (m)

mc 2

⎡

⎣ ⎢

⎤

⎦ ⎥∫

Simple argument:Luminosity per volume = (Stellar mass energy)

x(Radiation efficiency)/(Time during which radiation is emitted)

“Radiation Efficiency”

IMF (Salpeter, Larson, Top-heavy)

Stellar data from Schaller et al. (1992); Schaerer (2002)

Sample Initial Mass Functions of Stars

Salpeter:

Larson:

Top-heavy:

( )

Rest-frame Spectrum of <>

NIRB Spectrum per SFR

€

υIυ / ˙ ρ *

The “Madau Plot” at z>7

You don’t have to take this seriously for now. We need better measurements!

How About Metal Production?

Is the inferred stat formation rate at z>7 consistent with the metal abundance in the universe? Did these early stars that are responsible fo

r the near infrared background over-enrich the metals in the universe too early?

White dwarf or neutron star

Type II SN Weak SN Black hole by fallback

Direct collapse to black hole

Pulsational Pair Instability SN

Pair Instability SN

Theoretical data for Z=1/50 solar from Portinari et al. (1998)

Metal Production (Z=1/50 solar)

The metal density now is 1.2 * 108 M Mpc-3

-> The upper limit from the near infrared background for a larson IMF is excluded, but most of the parameter space survives the metallicity constraint.

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 2

005) It would be “daunting” if, and only if, these baryons had rem

ained 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.

“Smoking-gun”: Anisotropy

Press-release from Kashlinsky et al.: Detection of significant aniso

tropy 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 12’x6’.

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!

What Are the Sources of the Near Infrared Background?

One candidate: Lyman-alpha emitting galaxies at z>7. What do we learn about them from the existing Lyman-alpha Emitt

er (LAE) searches? Subaru Deep Field

34 LAEs at z=5.7 (Shimasaku et al. 2006) 17 LAEs at z=6.5 (Taniguchi et al. 2005; Kashikawa et al. 2006) 1 LAE at z=7 (Iye et al. 2006)

LALA Survey 1 LAE at z=6.5 (Rhoads et al. 2004)

ISAAC/VLT No detection at z=8.8 (Willis et al. 2006; Cuby et al. 2007)

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 hori

zontally by rescaling the mass with M/L. One parameter fit!

€

N(> L) = Survey Volume( ) × dMdn

dMM (L )

∫

Cumulative Mass Function (Sheth-Tormen Mass Function)

If we stretch the horizontal axis by M/L, then we get…

Luminosity Function of LAEs (1): SDF at z=5.7

M/Lband=95-120

Luminosity Function of LAEs (2): SDF at z=6.5

M/Lband=85-100

Luminosity Function of LAEs (3): SDF at z=7 (from 1 LAE)

M/Lband~100

Luminosity Function of LAEs (4):VLT/ISAAC at z=8.8 (no detection)

M/Lband>7

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. It’s a luminosity integrated over instrument’s bandwid

th. It’s a luminosity after absorption and extinction.

Conversion:

€

M

Lband

=M

Lbol

Lbol

Lband

1

α esc

Getting Lbol/Lband From Model Spectrum

A sample spectrum for a galaxy of Z=1/50 solar with a Salpeter IMF. The intrinsic equivalent width of Lyman-alpha = 483 angstroms.

Lband/Lbol: How Much Light Are We Losing?

Lower metallicity -> Larger Lyman-alpha We don’t lose much light -> less correction neces

sary. Hence, larger Lband/Lbol.

Very insensitive to the IMF

Main Result: Inferred (M/Lbol)/esc

(M/Lbol)/esc is remarkably stable from z=5.7 to 7! No detection of sources at z=8.8 is consistent with t

he expectation. We see no evidence for the evolution of (M/Lbol)/esc

from z=5.7 to 8.8.

What Do Our Results Imply? LAEs are normal galaxies, if:

M/Lbol~10, if a good fraction of Lyman-alpha photons survived, es

c~0.5. The predicted EW is consistent

with observation, EW~50-300 angstroms, if the metallicity is “normal”: Z=1/50-1 solar.

LAEs are starbursts, if: M/Lbol~1, if esc~0.05-0.1. The predicted EW is consistent

with observation, if the metallicity is low: Z=0-1/50 solar.

No evidence for the end of reionization! No evidence for the ev

olution of esc, unless esc goes down and M/Lbol goes up by the same amount to keep (M/Lbol)/esc constant.

You can make it more complex.

Why not stretching it vertically as well? “Duty cycle”, . (Haiman & Spaans 1999; Dijkstra, Wyithe & Haiman 200

6). In our model,

Why assuming a deterministic L-M relation? P(L|M): Probability for a halo of mass M to host a galaxy of luminosity, L.

(e.g., Cooray & Milosavljevic 2005) In our model, P(L|M)=delta[M-(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.

€

dMdn

dMM (L )

∫ → ε dMdn

dMM (L )

∫ P(L | M)

A Comment on Salvaterra&Ferrara (2006) They claim that the excess near infrared background cannot ori

ginate 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 d

etected in e.g., VLT/ISAAC field, where none was found. Their model galaxy is extremely bright: M/L~0.001. But, we don’t 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/L~0.001), • a moderate burst for a few hundred million years (M/L~0.1-1), or • a normal star formation (M/L~10).

SF(2006) ruled out only the first possibility.

Reionization & CMB - 21cm correlationAlvarez, Komatsu, Dore & Shapiro 2006, ApJ, 647, 840

Doppler is aprojected

effect on CMB

21-cm maps resultfrom line-emission

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

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 reionizationBoth effects are sensitive to reionization

The cross-correlation is cleaner! In analogy to TE correlation of CMB, their cross correlation is more immune to sy

stematics because errors are uncorrelated between the two observations

The Effect is Easy to Understand

• Reionization positive correlation• Recombination negative correlation

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

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 won’t produce the cross-correlation, but will produce spurious signal in the auto-correlation.

There are various observational windows to the universe at z>7 before JWST. Near infrared background Lyman-alpha emitters

The current data of LAEs do notnot show evidence for the end of reionization up to z~7. On-going follow-up, deeper surveys with Subaru at z=7 and VLT at z=

8.8 are going to be very interesting! The excess near infrared background is likely caused by stars

withwith metals. We don’t need metal-free stars, which is a good news. Future lies in anisotropy: a better prediction is required for the data fr

om CIBER (launch in 2008) More ambitious future with 21-cm

The 21-cm data should be correlated with CMB for a conclusiveconclusive detection of the cosmic signal.

Summary