Can Gamma-ray Observations
Probe the Cosmic Infrared
Background Radiation?
Yoshiyuki Inoue(JAXA International Top Young Fellow @ ISAS/JAXA)

1

Cosmic Background Radiation
CMB Galaxies (Inoue et al. ’13)

-2

10

Pop-III Stars (Inoue et al. ’13)
AGNs (All)Radio-quiet AGNs (Inoue et al. ’08)
Blazars (Inoue and Totani ’09)
Radio Galaxies (Inoue ’11)

-3

2

-2 -1

-1

E dN/dE [erg cm s sr ]

10

10-4
10-5

Galaxies?

10-6

AGNs?

10-7
10-8
10-9
10-10 -6
10

10-4

10-2

100

102

104

106

Photon Energy [eV]
2

108

1010

1012

•

Blazars, star-forming galaxies and radio galaxies can explain the intensity
and the spectrum of the EGB

Cosmic Gamma-ray Background

Preliminary
Ajello at HEM14

As usual: it does not include the systematic uncertainty on the EGB!

• FSRQs (Ajello+’12), BL Lacs (Ajello+’14), Radio gals. (YI’11), & Star-

forming gals. (Ackermann+’12)Extragalactic Background Light (EBL)
100

iIi [nW/m2/sr]

10

1

Stars

Dust

Madau & Pozzetti ’00 (HST)
Elbaz et al. ’02 (ISO)
Papovich et al. ’04 (Spitzer)
Fazio et al. ’04 (Spitzer)
Xu et al. ’05 (GALEX)
Dole et al. ’06 (Spitzer)
Frayer et al. ’06 (Spitzer)
Gardner et al. ’00 (HST)
Berta et al. ’11 (Hershel/PEP)
Wright & Reese ’00 (DIRBE)
Wright ’04 (DIRBE)
Levenson et al. ’07 (DIRBE)
Levenson & Wright ’08 (DIRBE)
Bernstein ’07 (HST)
Matsuoka et al. ’11 (Pioneer)
Matsumoto et al. ’11 (IRTS)
Matsuura et al. ’11 (AKARI)
CambrØsy et al. ’01 (DIRBE)
Dwek & Arendt ’98 (DIRBE)
Gorijian et al ’00 (DIRBE)
Finkbeiner et al ’00 (DIRBE)
Hauser et al ’98 (DIRBE)
Lagache et al ’00 (DIRBE)
Edelstein et al ’00 (Voyger)
Brown et al ’00 (HST/STIS)
Albert et al ’08 (MAGIC)(X, zc)=(1.0, 0.0)
(X, zc)=(50.0, 10.0)(X, zc)=(100.0, 10.0)

0.1
0.1

1

10

100

h[µm]
4

1000

10000

YI+‘13aGamma rays are attenuated by EBL
Extragalactic Background Lightblazar

IACT
γEBL

γVHE

e+
e-

5

Blazars
49

FSRQ

Log10 iLi(erg s-1)

Log10 (νLν [erg/s])

48• Non-thermal emission from47

radio to gamma-ray

46• Two peaks

45• Synchrotron

44• Inverse Compton

4342

BL Lac • Luminous blazars tend to41

have lower peak energies-50

5
Log10 Ea (eV) [eV])
Log10 (Energy

10Fossati+’98, Kubo+’98,
YI & Totani ’09(Fossati+’98, Kubo+’98)IN 46323–2094, USA. Institució Catalana de Recerca i Estudis
Avançats (ICREA), Barcelona, Spain. 61Consorzio Interuniversitario
per la Fisica Spaziale (CIFS), I-10133 Torino, Italy. 62Dipartimento
di Fisica, Università di Roma “Tor Vergata,” I-00133 Roma, Italy.
63
Department of Physics, Center for Cosmology and Astro-Particle
Physics, Ohio State University, Columbus, OH 43210, USA.

Downloaded from www.s

EBL Constraints from Gamma Rays
*To whom correspondence should be addressed. E-mail:majello@slac.stanford.edu (M.A.); buehler@stanford.edu(R.B.); anita.reimer@uibk.ac.at (A.R.)†Present address: Naval Research Laboratory, Washington, DC
20375, USA.

LAT best fit -- 1 sigma
LAT best fit -- 2 sigma
Franceschini et al. 2008
Finke et al. 2010 -- model C
Stecker et al. 2012 -- High Opacity
Stecker et al. 2012 -- Low Opacity
Kneiske et al. 2004 -- highUV
Kneiske et al. 2004 -- best fit
Kneiske & Dole 2010
Dominguez et al. 2011
Gilmore et al. 2012 -- fiducial
Abdo et al. 2010

10

1

102

2

SCIENCEVOL 338

H.E.S.S. full dataset
H.E.S.S. high energy
H.E.S.S. contour(sys + statlow | full | high10z ≈ 1.0

Galaxy counts

Ackermann +’13

1

30 NOVEMBER 2012)

Direct measurements

z~1.0
10
Energy [GeV ]5

H.E.S.S. low energy

ME12 exclusion region

H.E.S.S.
Fermi

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encemag.org

H.E.S.S. collaboration: The EBL iλ Fλ [ nW m-2 sr -1 ]nfitiesthedicurethe
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University, 3-4-1, Okubo, Shinjuku, Tokyo 169-8555, Japan.
38
CNRS, IRAP, F-31028 Toulouse cedex 4, France. 39GAHEC,
Université de Toulouse, UPS-OMP, IRAP, Toulouse, France.
40
Department of Astronomy, Stockholm University, SE-106 91
Stockholm, Sweden. 41Istituto Nazionale di Fisica Nucleare,
Sezione di Torino, I-10125 Torino, Italy. 42Department of Physics
and Department of Astronomy, University of Maryland, College
Park, MD 20742, USA. 43Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 7398526, Japan. 44Istituto Nazionale di Fisica Nucleare, Sezione diRoma “Tor Vergata,” I-00133 Roma, Italy 45INTEGRAL Science
Data Centre, CH-1290 Versoix, Switzerland. 46Institute of Space

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λ [ µm ]Abramowski+’13
Fig. 5. Flux density of the extragalactic backgroundlight versus
wave1191 length. The 1σ (statistical) contours derived for several energy ranges
are described in the top-right legend. The systematic uncertainty isadded quadratically to the statistical one to derive the H.E.S.S. contour. Lower limits based on galaxy counts and direct measurements are(see also Gongrespectively& Coorayshown’13, with
Dominguez+’13)
empty upward
and filled downward pointing
triangles (extracted from Gilmore et al. 2012). The region excluded by
Meyer et al. (2012) with VHE spectra is represented by the dashed area.

• Fermi and H.E.S.S. derived the EBL opacity or intensity using the

combined spectra of blazars.

• Inconsistent with the NIR EBL excess.
Table 6. Measured normalization of the EBL optical depth, corresponding to the 1σ (statistical) contours shown in Fig. 5.

τ/τ spectra.
λ −λ
λF (λ )−λF (λ )• They assume simple log-parabola or power-law
measured

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Dark Energy & Gamma rays?
The Astrophysical Journal Letters, 771:L34 (6pp), 2013 July 10

Domı́nguez & Prada

The Astrophysical Journal(6pp),
2013aJuly
10
Our Letters,
analysis is771:L34
based onapplying
maximum
likelihood

Gamma-ray attenuation (This work)

Domı́nguez

E0/E0,f iducial

Ackermann+ 12
Domı́nguez+ 13

E0/E0,f iducial

Cosmic γ-ray horizon, E0 [TeV]

technique in order to find which CGRH models (and therefore
which Hubble constant) are favored by the CGRH data. In thiseCMB+BAO+Cepheids+SNe (Hinshaw et al. 2013)
analysis, the systematic uncertainties in the determination ofh=the Hubble constant are considered as well. These are measured
by applying our maximum likelihood methodology to the cases 3.0 Planck+WP+highL+BAO (Ade et al. 2013)h=(6pp), 2013 10
July 10& Pradathat bracket the evolving EBL uncertainties Domı́nguez
given in the
D11model.
h=Figure 1 (right panel) shows the predicted CGRH estimated 2.5 High-redshift galaxy clusters (Bonamente et al. 2006)h== 0.30adopting different values of the Hubble constant buthnormalized
Ackermann+ 12
3.0the values obtained for the CGRH model withatfiducialh = 0.40
Type Ia supernova (Riess et al. 2011)h=Domı́nguez+ 13
cosmological parameters h = 0.7, Ωm = 0.3, and Ωm = 0.7.
h = 0.50
Thiswith 2.0h=
2.5 figure is intended to highlight the largest dependence
Gravitational lensing (Suyu et al. 2012)h=0.60
redshift. Hence, we can see that the highest sensitivity to the
Hubble constant is approximately in the range fromredshifth=h = 0.70
1
0.04
upcoming
2.0 to 0.1. This is a smoking gun for planningh =1.5 CMB+BAO (Anderson et al. 2012)0.80
h=
IACT observations and analysis of VHE sources, which will
= 0.90yield competitive constrains on H0 . The reason for h
thisoptimal1.5
Extragalactic HII (Chávez et al. 2012)h = 1.00
redshift is that this is the window where τ = 1 at energies
where
the optical depth flattens with energy (see Figure 17 in D11). 1.0For
1.0 lower redshifts, this occurs at τ < 1 and for higher redshifts
CMB (Hinshaw et al. 2013)at τ > 1. The flattening in τ produces that small changes in h
imply significant variations in E0 .
0.5 Galaxy clustering (Chuang et al. 2013)
0.5In the present work, the best-fit CGRH model to the ac0.1
tual data yield a value of the Hubble constant of H0 =+7.2
71.8+4.6
km s−1 Mpc−1 . In applying this proceCepheids (Freedman et al. 2012)−5.6 (stat)−13.8 (syst) 0.
1
0.01
0.01
0.1
1
0.01
0. 70
dure
we
have
to
assumethattheuncertainties
of
the
CGRH
data
50
55
60
65
75
80
85
90
Redshiftt(which include systematic
uncertainties
in
the
Fermi
Large
Area
[km
s−1 RedshiftMpc−1]H
0
Redshift
es of the Hubble constant, as predictedfrom the energy
empiricalscale;
EBL modelingby areD11 distributed
described in theare shown
Telescope
see D13)as text,
a Gaussian,Figure 2. The Hubble constant H0 derived from different methodologies.
smologywithmatterdensityΩ=
0.3
isassumed).
The
CGRH
data
are
taken
from
Ackermannetal.
(2012,
mis nottrue. Infit, the width
σfilledofFigure 1. Left panel: thewhich
CGRH
for necessarily
different values
ofthe
thelikelihood
Hubble constant,as predictedfrom
the empiricalEBLmodeling
by D11in theThemeasurement
presented
in thiswork is shown
withdescribeda red star. For
this text,
2 left panel but all the E0
error bars include the total uncertainty(statisticalplussystematic).
Right panel:same asmeasurement, the statistical uncertainties are shown with darker red, whereas thetheGaussian,
this
is,
∝
exp(−(x−µ)/(2σ)),isassumedastheseveralline styles
andwithcolorsflat
ΛCDM
cosmology with matter density Ωm = 0.3total
is assumed).
The CGRH data are taken from Ackermann et al. (2uncertainties (statistical plus systematic, added in quadrature) are shown
Hwith
derivedfor the fiducial
cosmologyh = (a0.7between
and Ω
0.3.lowerm =themean value
and upper uncertainty of the data
lighter red.
The systematic).
combined valueRight
presented
by Hinshaw(2012)
is butgreen
squares) and D13 (filled
blue As
circles).
Theabove,error thebars
includeerrors
the total
uncertainty with(statisticalplus
panel:
same etasal.left
panel
line
journal.)being fitted.
explained
statisticalare derived
shown with a blue hexagon, which includes CMB data from WMAP9 plus thevalues have been normalizedtheempirical
CGRH derived
forsystematicthe fiducial
cosmology withh = 0.7SPT
andandΩACT0.3. CMB or eCMB), BAO, and Cepheids
fromtothemaximum
likelihood
fit and theuncertainm =(extended
ground-basedties are then accounted for the EBL modeling. We notice thatplus SNe measurements. The CMB+BAO measurement by Anderson et al.
(Acolorversionof
thisfigureisavailable
intheonlinejournal.)(2012) includes CMB data from WMAP7 and BAO from the Sloan Digital Sky
themodel uncertainties
areatasymmetric(see
Sectionthe EBL
understandingof the EBL
wavelengths
where
the 6.1
deE CONSTANT
Survey-II luminous red galaxy sample plus data from the Baryon OscillationinD11) isanduncertainties
in thetectionnottherefore
possiblealso
yet theandsystematicthe convergenceof different
ATION
Spectroscopic Survey (BOSS). The results from the Planck Space Telescope
Hubbleconstant estimation.
combined with WMAP polarization low-multipole likelihood (WP) plus highmethodologies.
The value of H0 obtained here, based on γ -ray attenuation,
al Background
resolution CMB data (highL and BAO; Ade et al. 2013) are shown with aunderstanding
ofa shaded
the region
EBLis showing
at wavelengths
where
3. MEASURINGTHE
HUBBLEsquare. As a reference,
the H0 value from thewith a total
accuracyof aboutCONSTANT
18%, is in good agreement with thegreen
Cepheids distance ladder.
e constant from γ -rayFROM
thatγof-RAY
other present-day
as shown in Figure 2. Our tection
3.2.methods,
Methodology
is not possible yet and the convergence of
ATTENUATION(A color version of this figure is available in the online journal.)
estimate is compared with the Hubble constant and its uncerecades ago by Salamon
methodologies.
tainties
obtainedusing
the distanceladdersof Cepheids(FreedWebase
ourestimationoftheHubbleconstantonthethe γ -ray experiments
3.1. TheoreticalandObservational
Backgroundman etal. 2012),
type Ia supernovae(SNe; Riess et al. 2011),

Dominguez & Prada ’13

Dominguez & Prada ’13• Derive the cosmic expansion rate using gamma-ray horizon.
• Future data may allow to constrain cosmologicalparameters.

Spectra Assumption• Log-parabola (+ exp. cutoﬀ )• Single power-law (+ exp. cutoﬀ )• SSC

>100 GeV Gamma Rays from z=1.1 & z>0.6– 21 –PKS 1424+240 at z > 0.6

PKS 0426-380 at z=1.1

The Astrophysical Journal Letters, 768:L31 (6pp), 2013 May 10

-9

10

1016
Contemporaneous Fermi LAT from Acciari et al. 2010

νFν (Jy Hz)

1015

-2 -1

E dN/dE [erg cm s ]Observed
EBL corrected (Franceschini et al. 2008)
EBL corrected (Inoue et al. 2013)
Broken PL model

Contemporaneous Fermi LAT Power-law Fit from Acciari et al. 2010
VERITAS Observed VHE Spectrum from Acciari et al. 2010
z=0.6035 Absorption-corrected Spectrum using Doming uez et al. 2011

14

10

-10

10

z=0.6035 Absorption-corrected Spectrum using Gilmore et al. 2012
z=1.2 Absorption-corrected Spectrum using Dominguez et al. 2011

1013

2

1012
-11

10

0.1

Fermi
1

1011

10
Energy [GeV]100

Fermi + VERITAS
1

10102 Energy (GeV) 103

Tanaka,YI, +’13
Figure 3. Gamma-ray
peak of the spectral energy distribution of PKS 1424+240, with LAT (squares andFurniss
power-law fit +’13
contour) and V

circles) taken from Acciari et al. (2010). An upper limit at 750 GeV is shown with a downward pointing arrow. The LAT data have been sewith the VERITAS observations. The absorption-corrected VHE spectrum is shown with the gray circles, using opacities from the D
Fig. 4.— SED of PKS 0426−380 derived from the Fermi -LAT data accumulated during themodel. For reference, the absorption-corrected points using the Gilmore et al. (2012) model are shown in open circles, with errors (not d
et al. (2011)
most energetic flaring state spanning MET 280000000 (17:46:38 for
UTthe
onDomı́nguez
2009 November15) deabsorbed points. The LAT power-law fit has been extrapolated up to VHE (dashed red line). Power-lafull range (0.5–500 GeV) are shown in the blue dashed and dotted lines, respectively, with fitting results in Table 2. To bring the first ab
to 302000000 (08:53:18 UT on 2010 July 28; see also the black horizontal
linetoinmatch
Figurespectral pointthe2).
LAT observed spectrum, the blazar needs to be corrected for absorption expected for z ≈ 1.2, shown by blue
deabsorption is off-scale).
The observed spectrum is denoted by black squares and the highest energy bin is a 95%(A color version of this figure is available in the online journal.)
confidence level upper limit. The spectra corrected for the EBL-related attenuation, using• Distant very high energy (VHE) sources show spectral

not expectedby standard
blazar emission models, but is only
the EBL models of Franceschini et al. (2008) and Inoue et al. is(2013),
are represented
byhardening.

about two standard deviations at the redshift lower limit.
red circles and blue triangles, respectively. A broken power-law model
the the LAT and VERITAS absorptionA which
breakmaximizes
betweenapparent. This discrepancy is not likely an
likelihood for the 0.1–300 GeV Fermi -LAT data is also indicatedcorrectedwith black data
dashedisline.
issue of instrumental cross-calibration, as agreement between
VERITAS and LAT observations has been found for other contemporaneous blazar observations(e.g., Aliu et al. 2011, 2012).
10
A portion of this feature may be due to a small level of un-of the blazar. It has been shown thatrays by a broad-line region (BLR) can
law spectra in bright LAT-detected bla2010). However, this type of absorpti
expected for an intermediate-/high-synsuch as PKS 1424+240, expected to eenvironment (Böttcher & Dermer 2002;
The absorption-corrected VHE point

Is VHE Spectral Hardening Universal?

physical Journal, 768:197 (17pp), 2013 May 10

10

Inoue et al.

The Astrophysical Journal Letters, 751:L11

-9

-10

10

H 2356-309
z = 0.165

RX J0648.7+1516
z = 0.179

1ES 1218+304
z = 0.182

1ES 1101-232
z = 0.186

3

-11

10

-12

2

10-13
-9
10
-10

10

2.5
1ES 0347-121
z = 0.188

RBS 0413
z = 0.19

1ES 1011+496
z = 0.212

2

1ES 0414+009
z = 0.287

-11

10

∆Γ

2

E dN/dE [TeV/cm /s]

10

-12

1.5

10

-13

1

10
-9
10

-10

10

0.5

-11

10

-12

10

-13

10

S5 0716+714
z = 0.31
0.1

1

4C+21.35
z = 0.432
10 0.1

3C 66Az = 0.444
1

10 0.10

3C 279z = 0.5362
1

10 0.1

1

10

0

0.2

0.4

z

0.6

z

0.8

Figure 1. Spectral change,∆Γ= ΓTeV −
ΓGeV
Essey
&
Kusenko’12
Energy [TeV]
Energy [TeV]
Energy [TeV]
Energy [TeV]
observed by Fermi. Data points from the Fermi
Same as Figure 13, but for sources at z > 0.15. References for the data are H 2356-309 (Aharonian et al. 2006b), RX
J0648.7+1516 (Aliu et al. 2011),
LAT Collaboration 2011) were separated into thr
YI+‘13a304 (Acciari et al. 2009b), 1ES 1101−232 (Aharonian et al. 2007c), 1ES 0347−121 (Aharonian et al. 2007a), RBS 0413 (Aliu et al. 2012), 1ES 1011+496
inverted triangles), intermediate sources (green tr. 2007b), 1ES 0414+009 (Abramowski et al. 2012a), S5 0716+714 (Anderhub et al. 2009), 4C+21.35 (Aleksić et al. 2011a), 3C 66A (Aleksić et al. 2011b),(Albert et al. 2008).
(blue diamonds). The lines are the best fits to Eq
rsion of this figure is available in the online journal.)(dashed line) and (Γp − Γs ) = 0.995 (solid line).
(A color version of this figure is available in the o• Spectra of blazars at z > 0.15 show hardening from a few

hundred GeV.

ectra above several hundred GeV (see also Finke et al.

lain such intrinsically hard spectra, some authors havesuggested secondary cascade components generated

model of hierarchical galaxy formation, into which Pop-III stars
were incorporated in a simplified fashion. Our baseline model isconsistent with a wide variety of observational
11 data for galaxies
effect would increase ∆Γ because the var
below z ∼ 6 (Nagashima & Yoshii 2004; Kobayashi et al. 2007,

Secondary Gamma Rays? Stochastic Acceleration?

TheJuly
AstrophysicalJournal, 740:64 (9pp), 2011 October 20
Lefa, R
The AstrophysicalJournalLetters, 771:L32 (5pp), 201310
Takami, Murase, & Dermer
KUV
00311-1938(z=0.61)
1ES 0229+200 (z=0.1396)
1ES 0229+200 (z=0.1396)-10
Secondary
Gamma
Rays
Stochastic
Acc.
10
γ-induced (low IR)
-10
-9.5

10

10-13

-11.5

-14

-14

10
-12

10-15
10
10

10

11

12

10
E [eV]

10

13

-15

14

10

10

-12.5

Takami+’13

14

10Fv ∝ v 1/3-11

H.E.S.S. I

-2 -1

-13

-12

10

Fv ∝ v 1/3

10

CTA

-10.5

2

F(>10 GeV) [10-9 cm s ]

10

-12

3

10-11E Exp[-E/Ec]

F(>E) [cm s ]-112

γ-induced (low IR)
γ-induced(best fit)
H.E.S.S. lowlevel EBL
(low IR)
H.E.S.S.CR-induced
high level EBL
CR-induced
(best
fit)
SWIFT

E Exp[-(E/Ec) ]

-10

2

10

γ-induced (best fit)
CR-induced (low IR)
CR-induced (best fit)Becherini et al. (2012)
H.E.S.S. I

log vFv [erg.sec.cm
]
-2 -1

-1

E2 FE [erg cm-2 s ]

10

2
1

CTA

0
54500 55000 55500 56000 56500
Modified Julian Day

10 16

10

18

11

20

12

22
10
log v [Hz]E [eV]

24

13

10 26

Lefa+’1110
28

14

10. Hard spectrum blazar 1ES 0229+200 at z = 0.139 with SED modeled within an SSC approach using Maxwellian-type electron distrib
Figure 1. SEDs calculated for gamma-ray-induced (red) andFigure
UHECR-induced
used
are
theIR
same
as in Figure 3. Data
points2.
shown
in the figure
from Zacharopouloutoet al.
whereintheFigure
intrinsic (de-absorbed)
FigureIntegral
fluxarecorresponding
the(2011),
SEDs
1 (KUV sou(blue) cascade scenarios for KUV 00311−1938 (z = 0.61) using
low(thick)derived based on the EBL model of Franceschini et al. (2008) with (1) EBL level as in their original paper (“low-level EBL”) and (2) (maximum
00311−1938) with the H.E.S.S. I integral sensitivity (presented by Y. Becherini
and best fit (thin) EBL models deduced by Kneiske et al. (2004)bywith
theofanalyzed
a factor
1.6 (“high-level EBL”).
in Rencontres de Moriond 2009; http://moriond.in2p3.fr/J09/) and the integral
LAT data (green) with a H.E.S.S. preliminary spectrum (magenta;
Becherini(A color versionof this figure is available in the online journal.)
sensitivity goal of CTA for a 50 hr observation (Actis et al. 2011). The inset
et al. 2012). We take s = 1.76. The isotropic equivalent energy of input gamma
shows a >10 GeV light curve with 16 equal time bins, each lasting 90.3 days.
rays for the gamma-ray-induced cascade Liso
source protons forγ and of UHECRthe
Derishev, E. V., Aharonian, F. A., Kocharovsky,
V. V., &high low-energy cutoffs
neededin leptonic
synchrotronThelight curveis consistent
with a constant
flux
hypothesis
with χr2 = 0.95
iso
46
−1
47
−1
2003,
Phys.
Rev.
D,
68,
043003erg
s , rea UHECR-induced cascade Lp are 3.5×10 erg s and 1.1×10
Comptonmodelsfor the hard
spectrumsources.only from finite flux points.
which
is calculatedDermer, C. D., & Schlickeiser, R. 1993, ApJ, 416, 458
spectively. The differential sensitivity curve for a 50 hr observation
with H.E.S.S.
Althoughour main purpose here is not to fit data, Figure 10
Essey, W., Kalashev, O., Kusenko, A., & Beacom, J. F. 2
(A color
versionof this figure
is available
in the online journal.)
I (http://www.mpi-hd.mpg.de/hfm/HESS/pages/home/proposals/;line),
showsdashedthat a Maxwellian-type
electrondistribution
could also
Franceschini, A., Rodigliero, G., & Vaccari, M. 2008, A
Fritz, K. D. 1989, A&A, 214, 14
provide(CTA;a satisfactory
and the 50 hr sensitivity goal of the Cherenkov Telescope Array
Actis explanation for the hard TeV component
Georganopoulos, M., Kirk, J. G., & Mastichiadis, A. 200
in 1ESet al. 2011; dotted line) are also plotted. The flux lower thanthe0229+200.
sensitivity-10
Giebels, B., Dubus, G., & Khélifi, B. 2007, A&A, 462, 2
Our results
illustrate that even within
10 a leptonic synchrotroncurve can be achieved under a relaxed criterion of wider energy-bins
and lower
Gould, R. J., & Schréder, G. P. 1967, Phys. Rev., 155, 14
γ-induced(lowIR) ApJ, 383, L7
Comptonapproachrelatively
hard
intrinsic TeV source spectra
Henri,
G., & Pelletier,G. 1991,
significance required to estimate flux in each bin.
γ-induced(bestfit)6, 317
may be encountered under a variety of conditions. While thisKardashev,
N. S. 1962,
SvA,(A color version of this figure is available in the online journal.)
CR-induced(low IR)
Katarzyński,K., Ghisellini,G., Tavecchio, F., Gracia, J.,
may be reassuring, the possibility10of-11having such hard source
MNRAS,
368,
L52
CR-induced
(best
fit)
spectra within “standard models” unfortunately constrains the
Kifune, T. 1999, ApJ, 518, L21
potential of extracting limits on the EBL density based on γ -ray
Krawczynski, H., Coppi, C. S., & Aharonian, F. 2002, M
observationsof blazars, one of the hot-12
topics currently discussed
Longair, M. S. 1981, High Energy Astrophysics (Creproduced by both gamma-ray- and UHECR-induced
cascade10 instruments.
University Press)in the context of next generation VHE• Secondary gamma rays from cosmic rays along line of sight(Essey & Kusenko ’10, Essey+’10, Essey+’11, Murase+’12, Takami+’13)• Stochastic acceleration can generate hard electron spectra(Stawarz & Petrosian ’08, Lefa+’11, Asano+’14).

-2 -1) [cm s ]• Lepto-hadronic scenario (Inoue-san’s talk).

]scenarios between 10 and 100 GeV. The UHECR-induced cas12
cade predicts larger flux above 200 GeV and harder
spectrumWe thank
S. Kelner and S. Wagner for helpful discussions.

Maraschi, L., Ghisellini, G., & Celotti, A. 1992, ApJ, 39
Medvedev, M. V. 2006, ApJ, 637, 869

Direct Measurement of EBL

Astrophysical Journal, 737:2 (19pp), 2011 August 10

Matsuura et al

100
ZE

CMB

Surface brightness Iν [MJy/sr]

10

1
ZL
0.1

0.01

ISD

0.001

0.0001

DGL

1

SL

10

1 00

wavelength [µm]1 00 0

Matsuura+’11

re 1. Summary of the results of previous CIB measurements in the infrared and submillimeter wavelength ranges with from the following space missions
BE/DIRBE (diamonds; Hauser et al. 1998) as upper limits, COBE/FIRAS (shaded region in the submillimeter range; Fixsen et al. 1998), IRAS and ISO (thiwith downward arrows at 60 and 90 µm and cross in 150–180 µm, respectively; Juvela et al. 2009), IRTS (shaded region in the near infrared; Matsumoto et a5), and HST (open triangles in the near infrared; Thompson et al. 2007). For comparison, we also show various foreground emission components of the dark sky
acal light (ZL), zodiacal emission (ZE), starlight (SL; K > 9 mag), diffuse Galactic light (DGL), the Galactic cirrus (ISD), and the CMB. The integrated flu
the galaxy counts, obtained by deep surveys from the ground in the near-infrared and submillimeter ranges and via space telescopes in the mid- and far-infrare, Spitzer, and AKARI) (Totani et al. 2001; Kawara et al. 1998; Puget et al. 1999; Matsuhara et al. 2000; Kawara et al. 2004; Dole et al. 2004; Frayer et al. 2006asuura et al. 2007; Shirahata et al. 2008), is indicated by the filled triangles connected with thin lines. Stacking the 24-µm galaxies for the Spitzer/MIPS ma• Foreground: Zodiacal light, Diﬀuse galactic light, Star light.

Direct Measurement of EBL
No. ]urnal, 736:119 (14pp), 2011 August 1

Extragalactic Background Light Spectrum with

Matsuoka et al.

Pioneer 10/11

IRTS
AKARI

Matsuoka +’11

Tsumura +’13

urements of the cosmic background (filled symbols) and the integrated brightness of galaxies (open symbols) at UV, optical, and near-IRc background measurements include the UV upper limits (blue arrows) at 0.10 µm obtained from the Voyager/UVS (Edelstein et al. 2000)
HST/STIS (Brown et al. 2000), the claimed detections at optical wavelengths using the HST/WFPC2 (Bernstein 2007, green squares) and4. Spectrum of EBL and integrated light of galaxies. Filled plots show EBL by va
using the COBE/DIRBE [Gorjian et al. (2000), green diamonds; Wright (2001), purple diamonds; Cambrésy et al. (2001), blueFig.
diamonds;
monds; the wavelengths of these measurements are slightly shifted relative to each other for clarity] and the IRTS (Matsumoto etal. 2005,
thisstudy, and open plots shows the integrated light of galaxies by deep observationtars are the Pioneer/IPP results of this work, while the red solid line with arrows between 0.8 and 4 µm represents the HESS upper
limits data. Solid curve shows a model spectrum of the integrated light of galawide-band
The integrated brightness of galaxies come from the HST/STIS measurements at UV (Gardner et al. 2000, squares), the HDF compilation
rest-frame K-band galaxy luminosity function up to redshift 4 (Domı́nguez et al. 2011
dau & Pozzetti 2000, triangles), and the Spitzer/IRAC measurements at near-IR wavelengths (Fazio et al. 2004, diamonds).

• Pioneer 10/11 measurements are consistent with galaxy

counts.

Table 4
COB Brightness and Mean DGL-to-100 µm Brightness Ratios ad0

it in case of AKARI’s detection limit of point sources (mK = 19).

this correlation to the higher Galactic latitude regions in
our method. However, this assumption is obviously too
(µm)
(bgu)
(nW m−2 sr−1 )(bgu [MJy sr−1 ]−1 )(dimensionless)simple. For example, UV radiation field at high Galactic
0.44
1.8 ± 0.9
7.9 ± 4.0
3.2 ± 0.1
(2.1 ± 0.1) ×10−3
latitude is weaker than that at Galactic plane (Seon et
0.64
1.2 ± 0.9
7.7 ± 5.8
3.4 ± 0.1
(4.6 ± 0.1) ×10−3
al. 2011), therefore the PAH molecules are less excited athigh Galactic latitude than Galactic plane. This considwavelength range is much more controversial. Matsumotoal.
erationetindicatesthat the gap around 3.3µm could not be
is consistent with the previous observations,(2005)
claim
detectionofthestrongnear-IR
CIB
based
on
the
E is also present in the diffuse ISM with the
EBL origin but Galactic origin.
Infrared Telescope in Space (IRTS) data. Their CIB values are
ness. It confirms the finding of Gordon et al.
We obtained new spectral result of EBL at >4 µm, and
14COBE/DIRBE
marginally consistent with the results from thehe same conclusion from analysis of the IPP
we cannot confirm the excess over the integrated light ofWavelength

COB Brightness

DGL-to-100 µm Ratio ad0• Recent AKARI measurements are consistent with IRTS.
• EBL peak at near infrared?

Earth must be ddiﬀuse backgrou
candidate. Howµm cannot be gcold dust (<30 K
by the Oort clo∼ 104 − 105 au i
The second po
ist numerous fai
isotropic backgr

NIR Sky Fluctuation

Figure 8. Coherence, Cn4 ≡ (Pn4 (q) ∗ Pn4 (q))/(Pn (q)P4 (q)), for 1–4 (blue) and 2–4 (red) for EGS (left) and UDS!(right) fields. Open sym
where Pn4 < 0. The relative statistical uncertainties on the coherence resulting from cosmic variance are given by 12/Nq which is shown
valid at small C when all the power spectra can be assumed independent. With Nq plotted in Figure 1 this uncertainty is of the order of 100
The Astrophysical Journal, 742:124 (11pp), 2011 December 1
Matsumoto et al.
in the EGS field.
The Astrophysical Journal, 742:124 (11pp), 2011 December 1(A color version of this figure is available in the online journal.)

Matsumoto +’11

Kashlinsky+’12

Matsumoto +’11′′ )Figure 7.andSpectrumof the average fluctuation
large anglesBlack(100′′ –350
Figure 9. Field-averaged CIB fluctuations at 3.6 µm (left), 4.5 µm (middle),
the cross-correlation
poweratspectrum.
solid
line
(shownbyfilledcircles)iscomparedwiththeSpitzer
results(open
squares).
The
remaining known galaxies from Sullivan et al. (2007) who state that normal galaxies at Vega magnitudes from 22.5 to 26 can fit the observe
open circles represent the spectrum of the correlating component normalized to(That claim, which also appears in the comments to their, pre-print posting,is contradictedby theirown
Figure 8 which
shows
the
the 2.4 µm
band. The solid line
indicates
a Rayleigh–Jeans
spectrum(∼λ−3), cleKAMM1 measurements.) Because Sullivan et al. (2007) present their results
only
for
3.6
µm
sources,
their
model
is
displayed
onlywhile the dotted line indicates the spectrum in Figure 20 of Fernandez et al. in th(2010). Thethe
verticalbars show
error.
show the residual fluctuations from Helgason et al. (2012), after reconstructing
near-IR
CIB1σfluctuationsof known galaxies at both 3of multiband galaxy luminosity function (LF) data. The shaded regions correspond to the high and low faint end of the LF data. At 3.6 µ
the black solid line although Helgason et al. find, on average, slightly lower levels than Sullivan et al. (2007). The dashed line shows the
3.6 µm the regression leads to PSN = 57.5 nJy nW m−2 sr−1 (or 4.8 × 10−11 nW2 m−4 sr−1 ) and at 4.5 µm the shot-noise levels are PSN(or 2.2 × 10−11 nW2 m−4 sr−1 ). Since the shot noise can be expressed as PSN ∼ SFCIB (>m0 ), it is presented in both sets of units. Bluethe high-z ΛCDM (toy)-model processed through the mask of each field and then averaged as described in Appendix B. It leads to theA5′ = 0.07(0.05) nW m−2 sr−1 at 3.6(4.5) µm. The thick solid red line shows the sum of the three components.
(A color version of this figure is available in the online journal.)• AKARI & Spitzer reported NIR background fluctuation at 2.4, 3.2,

3.6, 4.1 and 4.5 um (Kashlinsky+’05, ’07, ’12, Matsumoto+’11, Cooray+’12).

• 15-20% of CIB fluctuation is correlated with CXB (Cappelluti+’13).

Figure 3 shows that within the statistical uncertainties the
produced by the discreteness of the rem
fields in this study have the same power spectrum of the sourceisotropy of the measured signal, which is fu
subtracted fluctuations. Therefore, we averaged the two sets
Appendix A for five additional fields from-3 spectrum describing theof results to obtain an overall powerments, is consistent with it being of cos(Matsumoto+’11,
Cooray+’12)
CIB. The averages were weighted with the number of Fourier
the same shot-noise level, the measured
elements in each field as describedabove. The results of the CIB
agreement with our measurements at five′′ diameter circle centered on each pixel. The lower panel shows smoothed
Figure 6. Upper panel shows smoothed sky maps obtained byaveragingpixelswithina50
fluctuations after averaging over
(KAMM1–2) at smaller angular scales (!
15the individual fields are shownark maps obtained by the same procedure for the dark maps. The color scales shown in the bar below each map are chosen such that sky maps and dark maps havein Figure 9. The figure indicates the presence of significant
This section discusses the constraints• The angular power spectrum at large scales is close to the shapeof a Rayleigh-Jeans spectrum, λNo. ]Can we explain the NIR EBL excess
in spectrum and fluctuation?
Extragalactic Background Light Spectrum with AKARI IRC

5

Figure 2. Amplitude maps of the two-dimensional fluctuation spectra, [q 2 P2 (q)/(2π )]1/2 , in Fourier space. The results for the 2.4, 3.2, and 4.1 µm band are shown
from the left to the right. The grayscale bars below each map indicate amplitudes of the fluctuation in units of nW m−2 sr−1 .

AKARI

IRTS
AKARI

Matsumoto +’11

Figure 3. Upper panel shows the one-dimensional fluctuation spectra, [q 2 P2 /(2π )]1/2 in units of nW m−2 sr−1 , obtained by two-dimensional Fourier analysis as afunction of angular scale (2π )/q. Graphs correspond to the 2.4, 3.2, and 4.1 µm bands from left to right. Filled circles and open triangles show the fluctuation spectra
for sky and dark maps, respectively. The lower panel shows the fluctuation spectra of the sky after subtracting those of dark maps in quadrature. The straight lines
fluctuation
spectraof shot noisedue to unresolvedfrom
faint galaxies.
Allincluding
error bars represent 1σ error.
Spectrum of EBL and integrated light of galaxies. Filled plots showindicate
EBLthebyvariousdirectphotometry
space

Tsumura +’13

Fig. 4.
this study, and open plots shows the integrated light of galaxies by deep observations. Horizontal bars show the band widths ofresults
taken assequence alternatingtime, observed
while in caseB thewide-band data. Solid curve shows a model spectrum of the integrated lightof agalaxies
based onin theevolutionofthefor both subsets are consistent with those of the stacked
dark maps.
This indicates that the observed structure is indeed
to theearlier curveand latershows
halves aof scaled
our set. version
rest-frame K-band galaxy luminosity function up to redshift 4 (Domı́nguez subsets
et al. correspond2011), andbrokenofpresent
intheoriginal images and is of celestial origin.
For
bothcases,
we
obtainedtwostackedimages,
F1
and
F2,
by
it in case of AKARI’s detection limit of point sources (mK = 19).
We also examined the impact of masking on the fluctuation
applying the same procedure as the one described previously inspectra, since ∼ 53% of all pixels are masked. We constructed
this section. The fluctuation spectra of the difference between
a common mask that includes all pixels masked in any of threetwobe
stackedimages arealready,shown in Figure
Cases A andmust
detected
if it4. exists.
An isotropic
his correlation to the higher Galactic latitude regions in Earth these
B
are
shown
as
squaresandasterisks,
respectively,
while
the
anotherbands. The fraction of remaining pixels in images
ur method. However, this assumption is obviously too diﬀuse background from the Oort cloud could be wavelengthwith the common mask applied is ∼ 32%. We again performed
fluctuation spectra of the dark maps are shown by triangles. The• A component other than galaxies should significantly

contribute to the NIR EBL.

imple. For example, UV radiation field at high Galactic
atitude is weaker than that at Galactic plane (Seon etl. 2011), therefore the PAH molecules are less excited at

candidate. However, the very blue spectrum toward 1µm cannot be generated by thermal emission from very
4
cold dust (<30 K) at the Oort cloud. Scattered sunlightOUND AND EARLY STARSFirst stars ?
709• Lyman alpha photons from z~10

will redshifted to ~1 um at z=0.
• We might see the light for first stars.
• But, we need very high first starformation rate density.
No. 2, 2006

Fernandez & Komatsu ‘06

NEAR-IR BACKGROUND AND EARLY

Fernandez & Komatsu ‘06

on from z ¼ 7 to 15 with various assumptions about metallicity and initial mass spectrum.
(Z ¼ 0), while the right panel shows the metal-poor case (Z ¼ 1/50 Z'). The solid, dashed,
17
Fig. 6.— Cosmic star formation rate. The shaded region shows the star forss spectra, respectively. The thick black lines show the total spectrum, while the thin purple,
mation rate for m > 5 M$ constrained by the current data of the cosmic near-Fig. 7.— Ratio

Reionization Constraints

YI+’13a

YI+’13aNeutral Hydrogen Fraction

Electron Thomson scattering opacity• Ionizing photon emissivity of first stars can not violate theseobserved reionization data.
18

Constraints on First Stars
Cosmic Star Formation Rate Density [Msun/yr/Mpc3]

101
Raue, Kneiske, & Mazin ’09
Gilmore ’12
C = 3.0, fesc = 0.2
C = 3.0, fesc = 0.5
C = 1.0, fesc = 0.2

Fernandez &Komatsu ‘06

100

10-1

-2

10

10-3
Bromm & Loeb ’06
Trenti & Stiavelli ’09
de Souza, Yoshida, & Ioka ’11

10-4

0

2

4

6

8

10
Redshift z

12

14

16

18

20

YI+’14• Combining reionization and distant gamma-ray data (E<100 GeV).
• The required first star formation rate density is inconsistent withreionization data (e.g. Madau & Silk ’05; YI+’14)
19

LETTER RESEARCH

such that we do not need to invoke a new population of point sources on The required modification needed to explain the fluctuation data is,however, ruled out by the measured number counts and the redshift
the sky to explain the observations.
While keeping the shot-noise level the same, the measurements can distribution7. Because intensity anisotropies are measured, anothersuch that we do not need to invoke a new population of point sources on The required modification needed to explain the fluctuation data is,
be explained by any physical effect that boosts the two-halo term of the option is to introduce a luminosity component to the dark-matter
however,out bythethemeasurednumbercountsand the redshift
sky oftogalaxyexplainthe observations.
22
remain ruled
unmaskedwhenhosted brightgalactic
disks
halothemodel
clustering. One possibility is to increase the halo haloes that
7
Becauseintensity
are inmeasured,another
distribution
thegalaxies
shot-noiselevel
theclusteringsame, theamplitude
measurements
maskedas part of. theanalysis.
Such a anisotropies
possibility exists
themassesWhileof the keeping
faint, dwarf
so thattheiris arecan
22
is toof introduce
luminosity
component
to the dark-matterbe explainedby any physicaleffectinthat
the two-halo
the option
literaturein the form
diffuse haloastars
in the extended
stellar profile
increasedwith a corresponding
increase
theirboosts
large-scalebias factorterm. of22
haloesremainofunmasked
when
hostedbright galactic disks
galaxiesout tothat
distances
100 kpc (ref.
23).theIn ouranisotropy
halo model of galaxy clustering . One possibility is to increase theofhalo
measurements,
we maskgalaxies
arcsec, exists in theas thepartfaintestof thedetected
analysis.
Such toa 3–4
possibility
masses of the faint, dwarf galaxies so that their clustering amplitude
is are masked
2π/ℓ (arcmin)a22which removes
the light
from
theof
bulgesandhalodisks
of thosegalaxies.
To stellar profile
literaturein theform
diffusestars
in theextendedincreased withincrease 1.0
in their large-scale
100.0 a corresponding
10.0
0.1 bias factor .
remove thelightout
component,
we would
have
to mask
to a radius
100
ofdiffusegalaxies
to distancesof 100kpc(ref. 23).
In our anisotropy
IHL
greaterthan
10arcsecaroundeachgalaxy.
Thesurfacedensitymeasurements, we mask the faintest detected galaxiesofto 3–4 arcsec,
1-halo–1102π/ℓ (arcmin)
3.6 mmandis suchwe galaxies. To
galaxies down
AB-magnitude
mfrom
a
AB , 222-halowhichtoremoves
the light
theatbulges
disksthatof those
100.0
10.0
1.0
0.1
expect 2 to
3 galaxies
within alight
circleof radius 10we
arcsec.
Shot noise0
removethe diffuse
component,
wouldThus
havemasks
to mask to a radius
10–2 10which successfully remove the diffuse component leave no pixels on
IHL
greater than 10 arcsec around each galaxy. The surface density of
1-halothe map from which to measure the anisotropy power spectrum.
–1
22 at 3.6 mm is such that we
galaxies down to AB-magnitude m in ,10–3 102-haloExisting studies discuss this extended emissionAB
terms of the diffuse
2 to15,3explained
galaxies aswithina circleof radius
10 arcsec.
Shot noise
originatingin tidally
strippedstars Thus masks
intrahalo expect
light (IHL)
–2
–4
10 10
removethe diffuse
component
leave no pixels on
producedwhich
during successfully
galaxy mergers
and collisions.
The fractionof stripped
the map
which toofmeasure
the anisotropy
stars is expected
to from
be a function
the halo mass,
with more power
massivespectrum.
10–5 10–3
Existing
studies
discussofthis
emissionin13,14,24
terms. of the diffuse
haloes containing
a largerfractiontheextended
diffuse haloemission
3.6 μm
15
25,26
Low-z
, explained
aslightoriginatingin tidally stripped stars
lightthe(IHL)
is a significant
On galaxyintrahalocluster scales,diffuseintracluster
10–6 –4

Intracluster Halo Stars?

• Stars stripped from host galaxies• Intrahalo stars may create afluctuation peak at l~1000.

10•produced
Is thisalreadyduringpopulation
galaxy mergers and collisions.
The fraction oftaken
stripped

z>6

10–7
–5
10
2
10

103

104

0
is expected to be a function of the halo mass, with more massive
10stars

105

ℓ

10–6
100.0
100 10–7

10.0

102

103

10–1

10–3
10–4
10–5
10

1.0

0.1

104

100

100.0

10.0

Ref. 13
Ref. 25

10–1

100This study

105

ℓ

b
10–2

ℓ2Cℓ /2π (nW m–2 sr–1)2ℓ2Cℓ /2π (nW m–2 sr–1)22π/ℓ (arcmin)

Ref. 14

fIHL

binto account in galaxy counts?

haloes containing a larger fraction of the diffuse halo emission13,14,24.
Ref. 14
On galaxy cluster scales, the diffuse intracluster light25,26 is a significant

3.6 μmLow-zz>62π/ℓ (arcmin)

1.0

0.1

10–2

10–1

Ref. 13
Ref. 25

M31
MWThis study

10–1

10–3

M31

fIHL

ℓ2Cℓ /2π (nW m–2 sr–1)2ℓ2Cℓ /2π (nW m–2 sr–1)2

by major mergers.

MW

10–2

10–2
4.5 μm

–3
–6 10

109

1010

1011

1012

1013

1014

1015

Halo mass (M/M!)–3

10–7 10–4
102

10–5

103

104
ℓ

105

Cooray+’12
4.5 μmFigure 1 | The angular power spectrum of the unresolved near-infrared–6
background.10
Shown
is the total power spectrum ‘2 C‘ =2p of SDWFS at 3.6 mm

Figure 2 | The IHL10
fraction from diffuse stars as a function of the halo mass.
The dark and light blue shaded regions show the 95% and 68% range ofintrahalo light fraction fIHL relative to the total luminosity of the dark-matter
911
12
10analytical
10prediction
101413, valid for1014
haloes as a function of the10halo
mass10M10from an
5 0.mass
We showcase where
fIHL . 4 3 1024 and M . 5 3 1010 M[ and at zHalo(M/Mthe!)20
dark matter subhaloes on orbits passing within a critical radius of the host halo

1015

Cooray+’12

Summary• Gamma-ray observations constrain EBL with various

techniques.
• But, VHE distant sources show unexpected spectral

hardening.
• It may not be straightforward to constrain EBL further

through gamma-ray observations of blazars.
• Direct EBL measurement is hampered by foregroundemission (x~100 times higher flux).
• Another component appears in angular power spectrum.
21