Population 3 and Cosmic Infrared Background

A. Kashlinsky (GSFC)

• Direct CIB excess measurements

• CIB excess and Population 3

• CIB excess and γ-ray absorption

• CIB fluctuations – results from Spitzer data

• Interpretation of the Spitzer data and Pop 3

• Resolving the sources - prospects w. JWST

From Kashlinsky (2005, Phys Rep., 409, 361)

CIB measurements - summary

CIB due to J, H, K galaxy counts

IRAC deep galaxy counts (Fazio et al 2004)

From Kashlinsky (2005, Phys. Rep., 409, 361)

Claimed mean CIB excess

Diffuse background from Pop 3 (Santos et al 2003, Salvaterra & Ferrara 2003, Cooray et al 2003, Kashlinsky et al 2004)

)1(4

)(

2z

dt

dV

d

dMMLn

dt

dF

L

∫ M n(M) dM = Ωbaryon 3H02/8πG f* f* fraction in Pop 3

dV = 4 π cdL2(1+z)-1 dt ; L ≈ LEdd ∞ M ; tL = ε Mc2/L << t(z=20)

srm

nWfhf

G

c

RI

baryonbaryon

H2*

24*

5

2 007.0044.0102.1

4

1

8

3

CIB data give:

FNIRBE = 29+/-13 nW/m2/sr F(λ>:10μm) < 10 nW/m2/sr

This can be reproduced with

f* = 4 +/- 2 % for ε=0.007

γ - ray absorption and CIB

• γ γ → e+ e-

• σ ~ σT

• X-section peaks at 0.4 σT

at EγECIB=2 (mec2)2

Dwek et al (2006)

z ~ 0.13

Aharonian et al (2006)

z ~ 0.18

From Aharonian et al (2006)

Pop 3 live at z > 10; hence any photons from them were produced then so that nγ ∞ (1+z)3 or

4π/c Iν/hPlanck(1+z)3 per dlnE = 0.6 Iν(MJy/sr) (1+z)3cm-3

Sharp cutoff at ε = 260 (1+zGRB)-2 GeV

(Kashlinsky 2005, ApJL)

dz

d

Reasons why Pop 3 should produce significant CIB fluctuations

• If massive, each unit of mass emits L/M~105 as normal stars (~L๏/M๏)

• Pop 3 era contains a smaller volume (~k2ct*), hence larger relative fluctuations

• Pop 3 systems form out of rare peaks on the underlying density field, hence their correlations are amplified

Population 3 would leave a unique imprint in the CIB structure And measuring it would offer evidence of and a glimpse into the Pop 3 era (Cooray et al 2004, Kashlinsky et al 2004)

CIB fluctuations from Population III

z Have to integrate along l.o.s.

(Limber equation)

dtzqddt

dI

cqF A

Pq ))(()(1

)/2~( 122'2

22

This can be rewritten as

)(( 1 zqdFF ACIBCIB

*

32

22 )(

2

1)(

ct

kPkk

Fractional CIB fluctuation on scale ~π/q is given by average value of rms fluctuation from Pop 3 spatial clustering over a cylinder of length ct* and diameter ~k-1.

θPop 3?

with

Cosmic infrared background fluctuations from deep Spitzer images and Population III

(A. Kashlinsky, R. Arendt, J. Mather & H. Moseley

Nature, 2005, 438, 45

+ more coming up shortly)

Pop 3 templates from Santos et al (2002)

• Used 3 fields: one main (deepest – IOC or QSO 1700), 2 auxiliary

• The deepest field is ~ 6’ by 12 ‘ and exposed for ~ 10 hrs

• The test/auxiliary field have shallower exposures.

Image processing:

• Data were assembled using a least-squares self-calibration methods from Fixsen, Moseley & Arendt (2000).

• Selected a field of 1152x512 pixels (0.6”) w. homogeneous coverage.

• Individual sources have been clipped out at >Ncutσ w Nmask =3-7

• Residual extended parts were removed by subtracting a “Model” by identifying individual sources w. SExtractor and convolving them with a full array PSF

• Finally, the Model was further refined with CLEAN-type procedure

• Clipped image minus Model had its linear gradient subtracted, FFT’d, muxbleed removed in Fourier space and P(q) computed.

• In order to reliably compute FFT, the clipping fraction was kept at >75% (Ncut=4)

• Noise was evaluated from difference (A-B) maps

• Control fields (HZF, EGS) were processed similarly

Datasets in Spitzer analysis(Kashlinsky, Arendt, Mather & Moseley 2005)

Region lGal bGal lecl becl <tobs> mVega,lim

QSO 1700

(or IOC)

94.4 36.1 194.3 83.5 Ch 1-3: 7.8 hrs

Ch 4: 9.2 hrs

> 22.5 (Ch 1)

> 20.5 (Ch 2)

> 18.25 (Ch 3)

> 17.5 (Ch 4)

HZF (Ch 1-3) 217.5 34.6 135.0 -4.9 ~ 0.5 hrs > 21.5 (Ch 1)

> 19.5 (Ch 2)

> 17.0 (Ch 3)

HZF (Ch 4) 18.4 -10.4 285.0 5.0 ~0.7 hrs > 14.5

EGSF 96.5 58.9 179.9 60.9 ~ 1.5 hrs

← Image (3.6 mic)

Exposure →

5.8 mic 8 mic

3.6 mic 4.5 mic

Ncut=4

Pmap – Pnoise:

Possible sources of fluctuations

• Instrument noise (too low and different pattern and x-correlation between the channels for the overlap region)

• Residual wings of removed sources (unlikely and have done extensive analysis and results are the same for various clipping parameters, etc)

• Zodiacal light fluctuations (too small: at 8 mic <0.1 nW/m2/sr and assuming normal zodi spectrum would be totally negligible at shorter wavelengths)

• G. cirrus: channel 4 (8 mic) may contain a non-negligible component of cirrus (~0.2 nW/m2/sr), but given the energy spectrum of cirrus emission the other channels should have negligible cirrus. Also similar excess in control fields.

• Extragalactic sources: 1) Ordinary galaxies (shot noise contributes to small scales, but

clustering component small)

2) Population 3: M/L << (M/L)Sun

5.8 mic Ncut=2 8 mic

3.6 mic 4.5 mic

Correlation function

Signal comes from mAB > 26.1 at 3.6 micron

Extragalactic component of the CIB fluctuations: Pop 3 or not Pop 3?

• Fluctuations arise from mAB > 26 (correlation function does not change to Ncut < 2)

• The clustering component measured (δF ~ 0.1 nW/m2/sr at θ > 1 arcmin)

• The shot-noise component of fluctuations

(PSN < ~ 10-11 nW2/m4/sr)

Take 3.6 micron data as an example.

Any model must explain the following:

1. Magnitude constraint:

mAB > 26.1 (mVega~ 23.5) at 3.6 mic or sources with flux < 130 nJy

Even at z =5 these sources would have 6x108 h-2LSun emitted at 6000 A

Extrapolated flux from remaining ordinary galaxies gives little CIB (~0.1-0.2 nW/m2/sr)

mVega

2. Clustering component

1. At 3.6 mic the fluctuation is δF~ 0.1 nW/m2/sr at θ≥ 1 arcmin

2. At 20>z>5 angle θ=1` subtends between 2.2 and 3 Mpc

3. Limber equation requires:

)(( 1 zqdFF ACIBCIB w. *

32

22 )(

2

1)(

ct

kPkk

4. Concordance CDM cosmology with reasonable biasing then requires Δ of at most 5-10 % on arcmin scales

5. Hence, the sources producing these CIB fluctuations should haveFCIB >1-2 nW/m2/sr

3. Shot noise clues to where does the signal come from.

PSN= ∫ f(m) dFCIB(m) = f(<m>) FCIB(m>mlim)

where f(m)=f010-0.4m and dF=f(m)dN(m).

At 3.6 mic PSN=6x10-12 nW2/m4/sr

For FCIB ~ 2 nW/m2/sr, the SN amplitude indicates the sources contributing to fluctuation must have mAB>30.

Resolving sources of CIBConfusion allows for individual detection when there are < 1/40-1/25sources per beam

For the parameters above one expects the sources to have abundance of

<n> ~ F2CIB/Psn > 8 arcsec-2

To beat the confusion at 5-σ level at 3.6 micron one needs beam of

ωbeam < 1/25 <n> ~ 5x10-3 (FCIB/2 nw/m2/sr)-2 arcsec-2

or radius

Θbeam < 0.04 (FCIB/2 nW/m2/sr) arcsec

This is (just about) reachable with JWST

Conclusions

• Mean near-IR CIB excess may be smaller than what IRTS and COBE measurements indicated

• Its level can be probed with future GLAST measurements of high z GRB spectra

• Measurements of CIB anisotropies after removal of high-z galaxies give direct probe of emissions from the putative Population III era

• CIB anisotorpies from Spitzer data indicate a presence of significant populations around mAB ~ 30 or a few nJy producing at least ~ 2 nW/m2/sr at 3.6 micron

• Such populations may just about be resolved individually with JWST