Download (EBL).

LA Astro 8 May 2013
Measuring All the Light Since
the Big Bang with Gamma Rays
Exploring the Non-thermal Universe with Gamma Rays
On the occasion of the 60th birthday of Felix Aharonian
Barcelona, November 6 - 9, 2012
EBL
Extragalactic
Background Light
Joel Primack & Alberto Domínguez
The Detection of the
The Detection of the
Cosmic
γ
-ray
Horizon
Cosmic γ-ray Horizon
Wednesday, May 8, 13
The Detection of
o
Cosmic γ-ray Ho
Alberto Domíngue
(University of California, River
Extragalactic Background Light (EBL)
Joel Primack & Alberto Domínguez
Data from (non-) attenuation of gamma rays from blazars and
gamma ray bursts (GRBs) give upper limits on the EBL from the
UV to the mid-IR that are only a little above the lower limits from
observed galaxies. New data on attenuation of gamma rays
from blazers now lead to statistically significant measurements
of the cosmic gamma ray horizon (CGRH) as a function of
source redshift and gamma ray energy that are independent of
EBL models. These new measurements are consistent with
recent EBL calculations based both on multiwavelength
observations of thousands of galaxies and also on semianalytic models of the evolving galaxy population. Such
comparisons account for all the light, including that from
galaxies too faint to see. Catching a few high-redshift GRBs
with Fermi or low-threshold atmospheric Cherenkov telescope
(ACT) arrays could provide important new constraints on the
high-redshift star formation history of the universe.
Wednesday, May 8, 13
PILLAR OF STAR BIRTH
Carina Nebula in UV Visible Light
Wednesday, May 8, 13
PILLAR OF STAR BIRTH
Carina Nebula in IR Light
Longer wavelength light
penetrates the dust better
Longer wavelength gamma rays
also penetrate the EBL better
Wednesday, May 8, 13
PILLAR OF STAR BIRTH
Carina Nebula in IR Light
Longer wavelength gamma rays
also penetrate the EBL better
Wednesday, May 8, 13
Gamma Ray Attenuation due to γγ → e+e-
Illustration: Mazin & Raue
If we know the intrinsic spectrum, we can infer the
optical depth τ(E,z) from the observed spectrum. In
practice, we typically assume that dN/dE|int is not harder
than E-Γ with Γ = 1.5, since local sources have Γ ≥ 2.
More conservatively, we can assume that Γ ≥ 2/3.
Wednesday, May 8, 13
Local EBL Observations
Γ ≥ 1.5
Γ ≥ 2/3
Wednesday, May 8, 13
Evolution Calculated from Observations
Using AEGIS Multiwavelength Data
Alberto DomÍnguez, Joel Primack, et al. (MNRAS, 2011)
Wednesday, May 8, 13
0.7 ☐°
http://aegis.ucolick.org/
Wednesday, May 8, 13
χ SED Fitting
2
Le PHARE code for fitting the SWIRE templates in FUV, NUV, B, R, I, Ks, IRAC1, 2, 3, 4 and MIPS24
Quiescent
Starburst
AGN-type
Best SED Fits
Star-forming
Worst SED Fits
Domínguez+ 11
Wednesday, May 8, 13
SED-Type Evolution
Local fractions, z<0.2:
Goto+ 03, morphologically classified from Sloan
converted to spectral classification using results
from Galaxy Zoo
Skibba+ 09 ~6% blue ellipticals
Schawinski+ 09 ~25% red spirals
Results:
Maximum uncertainty due to
photometry and fit errors
35% red-type galaxies
65% blue-type galaxies
High-redshift universe, z>1:
Two approaches:
1. Keep constant the fractions of our last redshift bin (Fiducial Model), or
2. Quickly increase starburst population from 16% at z = 0.9 to 60% at z ≥ 2
We find that the differences in the predicted EBL are small except at long
wavelengths, affecting attenuation only for E ≥ 5 TeV.
Wednesday, May 8, 13
Domínguez+11
Local Luminosity Density
Domínguez+11
Wednesday, May 8, 13
Local EBL
Observations
Domínguez+
11
vs. Domínguez+11
Propagating errors in SED fits
and redshift extrapolation
Wednesday, May 8, 13
Γ ≥ 1.5
Γ ≥ 2/3
EBL Calculated by Forward Evolution using SAMs
When we first tried doing this (Primack & MacMinn 1996,
presented at Felix Aharonian’s first Heidelberg conference),
both the stellar initial mass function (IMF) and the values of
the cosmological parameters were quite uncertain. After
1998, the cosmological model was known to be ΛCDM
although it was still necessary to consider various
cosmological parameters in models. Now the parameters
are known rather precisely, and our latest semi-analytic
model (SAM) used the current (WMAP5/7/9) cosmological
parameters. With improved simulations and better galaxy
data, we can now normalize SAMs better and determine the
key astrophysical processes to include in them.
Remaining uncertainties include whether the IMF is
different in different galaxies (possibly “bottom-heavy” in
massive galaxies), feedback from AGN, the nature of submm galaxies, and the star formation rate at high redshifts.
Wednesday, May 8, 13
z=5.7 (t=1.0 Gyr)
Forward Evolution Present status of ΛCDM
“Double Dark” theory:
• cosmological parameters
are now well constrained
by observations
z=1.4 (t=4.7 Gyr)
Cluster Data
time
z=0 (t=13.6 Gyr)
Springel et al. 2005
Wednesday, May 8, 13
Wechsler et al. 2002
• mass accretion history of
dark matter halos is~1012
represented by ‘merger
trees’ like the one at left
Determination of σ8 and ΩM from CMB+
WMAP+SN+Clusters Planck+WP+HighL+BAO
Planck
●
WMAP9
●
WMAP7
●
WMAP5 ●
●
BOSS
Wednesday, May 8, 13
Galaxy Formation in ΛCDM
• gas is collisionally heated when perturbations ‘turn
around’ and collapse to form gravitationally bound
structures
• gas in halos cools via atomic line transitions
(depends on density, temperature, and metallicity)
• cooled gas collapses to form a rotationally
supported disk
• cold gas forms stars, with efficiency a function of
gas density (e.g. Schmidt-Kennicutt Law)
• massive stars and SNae reheat (and in small halos
expel) cold gas and some metals
• galaxy mergers trigger bursts of star formation;
‘major’ mergers transform disks into spheroids and
fuel AGN
• AGN feedback cuts off star formation
White & Frenk 91; Kauffmann+93; Cole+94;
Somerville & Primack 99; Cole+00; Somerville,
Primack, & Faber 01; Croton et al. 2006; Somerville
+08; Fanidakis+09; Guo+2011; Somerville, Gilmore,
Primack, & Domínguez 12 (discussed here)
Wednesday, May 8, 13
Some Results from our Semi-Analytic Models
z=0 Luminosity Density
Modelling of the EBL and gamma-ray spectra
Evolving Luminosity Density
WMAP1
WMAP5
re 2. Left: the luminosity density of the local universe. The solid black line is the WMAP5 model, and the dotted line is the C!CDM mode
Gilmore,
Somerville,
Domínguez
(2012)
er of wavelengths are shown from GALEX (blue circles), SDSS (red stars;
Montero-Dorta
& PradaPrimack,
2009), 6dF&(light
blue squares;
Jones e
SS (green stars; Cole et al. 2001; Bell et al. 2003). In the mid- and far-IR, the orange squares are from IRAS (Soifer & Neugebauer 1991),
Wednesday, May 8, 13
Some Results from our Semi-Analytic Models
Evolving Luminosity Functions
K-band
B-band
-1
-1
-1
-1
-2
-2
-2
-2
-3
-3
-3
-3
-4
-4
-4
-4
-5
-5
-5
-5
-6
-6
-6
18
20
22
24
18
20
22
24
-6
18
26
20
22
24
-1
-1
-1
-1
-2
-2
-2
-2
-3
-3
-3
-3
-4
-4
-4
-4
-5
-5
-5
-5
-6
-6
-6
18
20
22
24
26
18
20
22
24
26
18
20
22
24
18
20
22
24
-6
18
20
22
24
An advantage of the SAM approach is that it is
possible to compare predictions and observations
Gilmore, Somerville, Primack, & Domínguez (2012)
at all redshifts and in all spectral bands.
Wednesday, May 8, 13
Some Results from our Semi-Analytic Models
3.6, 8, 24 and 24, 70, 160, &
Number Counts in
850 μm Bands
UV, b, v, i, and z Bands
Somerville, Gilmore, Primack, & Domínguez (2012)
Wednesday, May 8, 13
Worst failure is at 850 μm
Modelling of the EBL and gamma-ray spectra
EBL from our Semi-Analytic Models
3195
Propagating D+11 errors in SED
fits and redshift extrapolation
WMAP1
Gilmore, Somerville, Primack,
& Domínguez (2012)
Wednesday, May 8, 13
from all but the nearest extragalactic sources. The change in the functional form of
the EBL means that a simple z-dependent scaling model is inadequate.
Evolution of the EBL
Physical Coordinates
Co-moving Coordinates
FIGURE 5. The evolution of the EBL in our WMAP5 Fiducial model. This is plotted on the left panel
The evolution of the EBL in our WMAP5 Fiducial model. This is plotted on the left panel in
in standard units. The right panel shows the build-up of the present-day EBL by plotting the same
standard
units. The right panel shows the build-up of the present-day EBL by plotting the
quantities in comoving units. The redshifts from 0 to 2.5 are shown by the different line types in the
same quantities in comovingkey
units.
The
fromFig.
0 to52.5
are shown by the different
in the
leftredshifts
panel. (From
of [9].)
line types in the key in the left panel.
Wednesday, May 8, 13
Gilmore, Somerville, Primack, & Domínguez (2012)
ments, and by the Large
Fermi gamma-ray space
AGILE (Tavani et al. 200
The Fermi LAT spends
and with its large area o
f
finding high-energy sour
685 high-energy sources
et al. 2010a). While the F
e
to ∼300 GeV, it has a mu
generation of ground-ba
se
ment is therefore most us
ef
threshold of these IACT
s,
EBL constraints availab
le
and gamma-ray bursts (G
paper by the Fermi collab
or
its on the EBL available
fr
the UV flux predicted in
presented here.
In this section and the f
effect of th
198Predicted
R. C. Gilmore
et
al.
Gamma Ray Attenuation
ments, and by
Increasing distance causes
Fermi
gammaabsorption features to
AGILE (Tavan
increase in magnitude
and
appear at lower energies.
The Fermi L
The plateau seen between
and
with
1 and 10 TeV
at low
z isits
a la
product of the
mid-IR high-en
finding
valley in the EBL spectrum.
685 high-energ
et al. 2010a). W
to ∼300 GeV,
generation of g
ment is therefo
threshold of th
EBL constrain
and gamma-ra
WMAP5 Fiducial
paper by the Fe
WMAP5 Fixed
its on the EBL
Domiínguez+11
the UV flux p
presented here
Gilmore, Somerville, Primack, & Domínguez (2012)
In this secti
Modelling of the EBL and gamma-ray spectra
3195
Figure 4. The predicted z = 0 EBL spectrum from our fiducial WMAP5 model (solid black) and WMAP5+fixed (dash–dotted violet) dust parameters, and
C!CDM (dotted black) models, compared with experimental constraints at a number of wavelengths. D11 is shown for comparison in dashed–dotted red with
the shaded area indicating the uncertainty region. Data: upward pointing arrows indicate lower bounds from number counts; other symbols are results from
direct detection experiments. Note that some points have been shifted slightly in wavelength for clarity. Lower limits: the blue–violet triangles are results from
HST and Space Telescope Imaging Spectrograph (STIS; Gardner et al. 2000), while the purple open triangles are from GALEX (Xu et al. 2005). The solid green
and red triangles are from the Hubble Deep Field (Madau & Pozzetti 2000) and Ultra Deep Field (Dolch & Ferguson, in preparation), respectively, combined
with ground-based data, and the solid purple triangle is from a measurement by the Large Binocular Camera (Grazian et al. 2009). In the near-IR J, H and K
bands, open violet points are the limits from Keenan et al. (2010). Open red triangles are from IRAC on Spitzer (Fazio et al. 2004), and the purple triangle at
15 µm is from ISOCAM (Hopwood et al. 2010) on ISO. The lower limits from MIPS at 24, 70 and 160 µm on Spitzer are provided by Béthermin et al. (2010)
(solid blue) and by Chary et al. (2004), Frayer et al. (2006) and Dole et al. (2006) (solid gold, open gold and open green, respectively). Lower limits from
Herschel number counts (Berta et al. 2010) are shown as solid red triangles. In the submillimetre, limits are presented from the BLAST experiment (green
points; Devlin et al. 2009). Direct detection: in the optical, orange hexagons are based on data from the Pioneer 10/11 Imaging Photopolarimeter (Matsuoka
et al. 2011), which are consistent with the older determination of Toller (1983). The blue star is a determination from Mattila et al. (2011), and the triangle
at 520 nm is an upper limit from the same. The points at 1.25, 2.2 and 3.5 µm are based upon DIRBE data with foreground subtraction: Wright (2001, dark
red squares), Cambrésy et al. (2001, orange crosses), Levenson & Wright (2008, red diamond), Gorjian et al. (2000, purple open hexes), Wright & Reese
(2000, green square) and Levenson et al. (2007, red asterisks). In the far-IR, direct detection measurements are shown from DIRBE (Schlegel, Finkbeiner &
Davis 1998; Wright 2004, solid red circles and blue stars) and FIRAS (Fixsen et al. 1998, purple bars). Blue–violet open squares are from IR background
measurements with the AKARI satellite (Matsuura et al. 2011).
Wavelength range
WMAP5 (fiducial)
WMAP5+fixed
C!CDM
D11
Optical–near-IR peak (0.1–8 µm)
Mid-IR (8–50 µm)
Far-IR peak (50–500 µm)
Total (0.1–500 µm)
29.01
4.89
21.01
54.91
24.34
5.16
22.94
52.44
26.15
5.86
24.08
56.09
24.47
5.24
39.48
69.19
"
C 2012 The Authors, MNRAS 422, 3189–3207
C 2012 RAS
Monthly Notices of the Royal Astronomical Society "
Wednesday, May 8, 13
versus
Table 1. The integrated flux of the local EBL in our models (WMAP5 with evolving and fixed
dust parameters, and the C!CDM model) and the model of D11. Units are nW m−2 sr−1 .
Gamma Ray Attenuation due to γγ → e+e-
Illustration: Mazin & Raue
If we know the intrinsic spectrum, we can infer the
optical depth τ(E,z) from the observed spectrum. In
practice, we typically assume that dN/dE|int is not harder
than E-Γ with Γ = 1.5, since local sources have Γ ≥ 2.
More conservatively, we can assume that Γ ≥ 2/3.
Wednesday, May 8, 13
Reconstructed Blazar Spectral Indexes
With our SAM based
on current WMAP5
cosmological
parameters and
Spitzer (Rieke+09)
dust emission
templates, all high
redshift blazars have
spectral indexes
Γ≥1.5, as expected
from nearby sources.
Γ=1.5
(Of course, the
spectrum could be
harder than Γ≥1.5.)
H 1426+428
1ES 0229+200
Wednesday, May 8, 13
mid-IR valley in the EBL spectrum.
With a 50 GeV
threshold, we
see to z≈1.5-3
with less than
1/e attenuation!
Cosmic Gamma-Ray Horizon
100 GeV
Threshold
50 GeV
Threshold
Gilmore, Somerville, Primack, & Domínguez (2012)
Wednesday, May 8, 13
DETECTION OF THE COSMIC γ-RAY HORIZON FROM
MULTIWAVELENGTH OBSERVATIONS OF BLAZARS
ApJ in press
May 2013
A. Domínguez, J. D. Finke, F. Prada, J. R. Primack, F. S. Kitaura, B. Siana, D.
Paneque
The first statistically significant detection of the cosmic γ-ray horizon (CGRH)
that is independent of any extragalactic background light (EBL) model is
presented. The CGRH is a fundamental quantity in cosmology. It gives an
estimate of the opacity of the Universe to very-high energy (VHE) γ-ray photons
due to photon-photon pair production with the EBL. The only estimations of the
CGRH to date are predictions from EBL models and lower limits from γ-ray
observations of cosmological blazars and γ-ray bursts. Here, we present
synchrotron self-Compton models (SSC) of the spectral energy distributions of
15 blazars based on (almost) simultaneous observations from radio up to the
highest energy γ-rays taken with the Fermi satellite. These SSC models predict
the unattenuated VHE fluxes, which are compared with the observations by
imaging atmospheric Cherenkov telescopes. This comparison provides an
estimate of the optical depth of the EBL, which allows a derivation of the CGRH
through a maximum likelihood analysis that is EBL-model independent. We find
that the observed CGRH is compatible with the current knowledge of the EBL.
Wednesday, May 8, 13
SED multiwavelength fits
A one-zone synchrotron/SSC model is fit to the multiwavelength data excluding the
Cherenkov data, which are EBL attenuated. Then, this fit is extrapolated to the VHE regime
representing the intrinsic VHE spectrum. Technique similar to Mankuzhiyil et al. 2010.
y
r
a
n
i
im
l
e
Pr
PKS 2155-304
z = 0.116
Variability time
scale 104 s (fast)
y
r
a
n
i
m
li
e
r
P
1ES 1218+304
z = 0.182
Variability time
scale 105 s (slow)
Domínguez+13
Wednesday, May 8, 13
Detection
of the
cosmic ET
γ-ray
horizon
DOM
ÍNGUEZ
AL.
H2356-309
= 0.165)
0 = None
PKS2155-304
(fast)(fast)
(z = (z
0.116)
E0 =E(0.77
± 0.17) TeV
22
10−11
11
10−12
10−1310 12 14 16 18 20 22 24 26 28
log10 (ν/Hz)
0
0
−3
−3
−1.5
−1.5
1.5
1.5
3
3
−9
10−10
2
2
10−11
1
1
10−12
10−1310 12 14 16 18 20 22 24 26 28
log10 (ν/Hz)
−1
−1
−2
−2
−3
−1.5
−3
−1.5
10−9
10−10
0
0
10−1310 12 14 16 18 20 22 24 26 28
log10 (ν/Hz)
1.5
1.5
−3
−1.5
−3
−1.5
10−10
10−11
10−12
10−1310 12 14 16 18 20 22 24 26 28
log10 (ν/Hz)
0.0
0.5
1.0
−0.5
0.0
0.5
1.0
−0.5
log10 (Energy/TeV)
log10 (Energy/TeV)
1ES1218+304 (slow) (z = 0.182) E0 = (0.46 ± 0.02) TeV
H1426+428 (slow) (z = 0.129) E0 = (13.24 ± 16.81) TeV
1.5
1.5
10−9
10−10
10−11
10−12
10−1310 12 14 16 18 20 22 24 26 28
log10 (ν/Hz)
−2
−2
10−12
10−9
−1.0
−1.0
−1
−1
10−11
0.0
0.5
1.0
−0.5
0.0
0.5
1.0
−0.5log (Energy/TeV)
10
log10
(Energy/TeV)
Wednesday, May
8, 13
1ES1101-232
(fast) (z = 0.186) E0 = (0.41 ± 0.02) TeV
−1.0
−1.0
10−1310 12 14 16 18 20 22 24 26 28
log10 (ν/Hz)
E2dN/dE [erg cm−2 s−1 ]
log
log
1010τ τ
1
1
0.0
0.5
1.0
−0.5
0.0
0.5
1.0
−0.5
log10 (Energy/TeV)
log10
(Energy/TeV)
1ES1218+304 (fast) (z = 0.182) E0 = (0.58 ± 0.02) TeV
H1426+428 (fast) (z = 0.129) E0 = (6.23 ± 7.64) TeV
10
10−12
−2
−2
10−1310 12 14 16 18 20 22 24 26 28
log10 (ν/Hz)
−1.0
−1.0
E2dN/dE [erg cm−2 s−1 ]
2
2
E2dN/dE [erg cm−2 s−1 ]
3
3
10−11
−1
−1
Domínguez+11
prediction
10−12
−3
−3
−1.5
−1.5
10−10
10−10
Best
fit polynomial
10−11
−2
−2
00
E2dN/dE [erg cm−2 s−1 ]
−1
−1
10
−9
10−9
E2dN/dE [erg cm−2 s−1 ]
10−10
log
log1010τ τ
00
10−9
E2dN/dE [erg cm−2 s−1 ]
log
log1010τ τ
11
H2356-309
(slow)
= 0.165)
0 = None
PKS2155-304
(slow)
(z = (z
0.116)
E0 =E(0.88
± 0.05) TeV
33
log
log
1010τ τ
22
E2dN/dE [erg cm−2 s−1 ]
33
E2dN/dE [erg cm−2 s−1 ]
6
10−9
10−10
10−11
10−12
10−1310 12 14 16 18 20 22 24 26 28
log10 (ν/Hz)
0.0
0.5
1.0
−0.5
0.0
0.5
1.0
−0.5log (Energy/TeV)
10
log10 (Energy/TeV)
1ES1101-232 (slow) (z = 0.186) E0 = (0.39 ± 0.01) TeV
−1.0
−1.0
1.5
1.5
16
Quasi-Simultaneous
Catalog
of
15
BL
Lacs
A. Domı́nguez et al.
Source
Mkn 421
Mkn 501
1ES 2344+514
1ES 1959+650
PKS 2005 489
W Comae
PKS 2155 304
H 1426+428
1ES 0806+524
H 2356-309
1ES 1218+304
1ES 1101 232
1ES 1011+496
3C 66A
PG 1553+113
(based on the compilation by Zhang et al. 2012)
Redshift
E0 ± ( E0 )stat ± ( E0 )sys [TeV]
0.031
0.034
0.044
0.048
0.071
0.102
0.116
0.129
0.138
0.165
0.182
0.186
0.212
0.444
0.500+0.080
0.105
11.14+9.56
8.44 ± 2.23
5.20+23.49
3.94 ± 1.04
None
None
2.04+0.30
0.31 ± 0.41
None
0.82+0.11
0.22 ± 0.16
None
0.55+0.31
0.24 ± 0.11
None
0.52+0.08
0.08 ± 0.10
0.40+0.03
0.02 ± 0.08
None
0.30+0.03
0.03 ± 0.06
0.23+0.05
0.03 ± 0.05
ED11 ±
ED11 [TeV]
9.72+1.85
3.17
+1.68
8.75 3.31
6.01+1.20
3.23
+1.02
5.12 2.99
1.83+0.34
1.06
+0.09
0.90 0.18
0.77+0.07
0.13
+0.06
0.68 0.11
0.64+0.05
0.10
+0.04
0.54 0.07
0.49+0.04
0.06
+0.04
0.48 0.06
0.43+0.03
0.05
+0.02
0.23 0.02
0.21+0.02
0.02
E0 is the CGRH (i.e., the energy at which the optical depth τ = 1) and ED11 is the energy Table 2. The 15 blazars in our catalog are listed with their estimated redshifts. The cosmic where τ = 1 for the Fiducial model of Domínguez, Primack, et al. 2011. None means that ( E0 )our given with
its statistical
and
(see
text for de
sys )mis
ethodology output no solution for systematic
the CGHR, uuncertainties,
sually because respectively
the SSC model failed.
discussed in Domı́nguez et al. (2011a) (ED11 ± ED11 ) is given as well. None means
that our m
Domínguez+13
CGRH.
Wednesday,
May 8, 13
Cosmic γ-ray
Horizon:
DOM
ÍNGUEZ ET AL. results
Cosmic γ-ray horizon [TeV]
10
101
n42
k
M
This
work
Domínguez+
13
Domı́nguez+ 11
13
1
n50
Mk
1
Propagating D+11 errors in SED
fits and redshift extrapolation
PK
S2
-4
005
89
100
PK
S2
-3
155
1E
10−1 −2
10
S
04
080
24
5
+
6
10−1
Redshift
04
3
+
8
121 -232
S
1E 101
S1
1E
3C
66A
15
PG
11
53+
3
100
Fig. 2.— Estimation of the CGRH from every blazar in our sample plotted with blue circles. The statistical uncertainties are shown
darker blue
statistical
plusour
20%
of systematic
uncertainties
are could
shownnot
with
lighter blue
The CGRH
Therelines
are 4and
outthe
of 15
cases where
maximum
likelihood
methodology
be applied
since lines.
the prediction
fromcalculated
the
the EBL model described in Domı́nguez et al. (2011a) is plotted with a red-thick line. The shaded regions show the uncertainties fro
synchrotron/SSC
model
was lower
than the detected
EBL modeling,
which were
derived
from observed
data. flux by the Cherenkov telescopes.
to use as conservative upper limits the results by Mazin
cally higher because the optical depth for these case
Domínguez+13
Two
other
cases
where
the
statistical
uncertainties
were
too
high
to
set any unity
constraint
on E0.
& Raue (2007) rather than the newer results by Meyer
comes
at energies
larger than the energies obse
Wednesday,
May 8, 13 that are based in a more constraining specet al. (2012)
by the Cherenkov telescopes. Therefore, in these
Istituto Nazionale di Fisica Nucleare, Sezione di Pisa I-56127
Pisa, Italy. 6Laboratoire AIM, CEA-IRFU/CNRS/Université Paris
Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif sur
Yvette, France. 7Istituto Nazionale di Fisica Nucleare, Sezione di
Trieste, I-34127 Trieste, Italy. 8Dipartimento di Fisica, Università
di Trieste, I-34127 Trieste, Italy. 9Istituto Nazionale di Fisica
Nucleare, Sezione di Padova, I-35131 Padova, Italy. 10Dipartimento di Fisica e Astronomia “G. Galilei,” Università di
Padova, I-35131 Padova, Italy. 11Istituto Nazionale di Fisica
Nucleare, Sezione di Pisa, I-56127 Pisa, Italy. 12Santa Cruz
Institute for Particle Physics, Department of Physics and
Department of Astronomy and Astrophysics, University of
California at Santa Cruz, Santa Cruz, CA 95064, USA.
13
Dipartimento di Fisica “M. Merlin” dell’Università e del
Politecnico di Bari, I-70126 Bari, Italy. 14Istituto Nazionale di
Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy. 15Laboratoire
Leprince-Ringuet, École Polytechnique, CNRS/IN2P3, Palaiseau,
France. 16Institut de Ciències de l’Espai (IEEE-CSIC), Campus
UAB, 08193 Barcelona, Spain. 17INAF-Istituto di Astrofisica
Spaziale e Fisica Cosmica, I-20133 Milano, Italy. 18Agenzia
Spaziale Italiana (ASI) Science Data Center, I-00044 Frascati
(Roma), Italy. 19Istituto Nazionale di Fisica Nucleare, Sezione
di Perugia, I-06123 Perugia, Italy. 20Dipartimento di Fisica,
Università degli Studi di Perugia, I-06123 Perugia, Italy. 21Center for Earth Observing and Space Research, College of Science,
George Mason University, Fairfax, VA 22030, USA. 22National Re-
Physics, AlbaNova, SE-106 91 Stockholm, Sweden. 28Royal
Swedish Academy of Sciences Research Fellow, SE-106 91
Stockholm, Sweden. 29IASF Palermo, 90146 Palermo, Italy.
30
INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, I-00133
Roma, Italy. 31Space Science Division, Naval Research Laboratory, Washington, DC 20375–5352, USA. 32Department of
Physical Sciences, Hiroshima University, Higashi-Hiroshima,
Hiroshima 739-8526, Japan. 33NASA Goddard Space Flight
Center, Greenbelt, MD 20771, USA. 34INAF Istituto di Radioastronomia, 40129 Bologna, Italy. 35Department of Astronomy,
Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto
606-8502, Japan. 36Department of Physics, Royal Institute of
Technology (KTH), AlbaNova, SE-106 91 Stockholm, Sweden.
37
Research Institute for Science and Engineering, Waseda
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 di
Roma “Tor Vergata,” I-00133 Roma, Italy 45INTEGRAL Science
Data Centre, CH-1290 Versoix, Switzerland. 46Institute of Space
and NASA Goddard Space Flight Center, Greenbelt, MD 20771,
USA. 51Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA. 52Institut für Astro- und Teilchenphysik
and Institut für Theoretische Physik, Leopold-Franzens-Universität
Innsbruck, A-6020 Innsbruck, Austria. 53Department of Physics,
California Polytechnic State University, San Luis Obispo, CA
93401, USA. 54Department of Physics, University of Washington, Seattle, WA 98195–1560, USA. 55Max-Planck-Institut für
Kernphysik, D-69029 Heidelberg, Germany. 56Space Sciences Division, NASA Ames Research Center, Moffett Field,
CA 94035–1000, USA. 57NYCB Real-Time Computing Inc.,
Lattingtown, NY 11560–1025, USA. 58Astronomical Observatory,
Jagiellonian University, 30-244 Kraków, Poland. 59Department of
Chemistry and Physics, Purdue University Calumet, Hammond,
IN 46323–2094, USA. 60Institució 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.
ABSTRACT The light emitted by stars and
The Imprint of the
accreting compact objects through the
Extragalactic Background history of the universe is encoded in the
intensity of the extragalactic background
Light in the Gamma-Ray light (EBL). Knowledge of the EBL is
important to understand the nature of star
Spectra of Blazars
formation and galaxy evolution, but direct
M. Ackermann, M. Ajello, et al.
measurements of the EBL are limited by
(Fermi), Science 338, 1190 (2012)
galactic and other foreground emissions.
Here, we report an absorption feature seen in the combined spectra
of a sample of
*To whom correspondence should be addressed. E-mail:
[email protected] (M.A.); [email protected]
gamma-ray blazars out to a redshift of z ∼ 1.6. This feature is caused
by attenuation
of
(R.B.); [email protected]
(A.R.)
address: Naval Research Laboratory, Washington, DC
gamma rays by the EBL at optical to ultraviolet frequencies and†Present
allowed
us to measure
20375, USA.
the EBL flux density in this frequency band.
derived com- bining the limits on the best-fit
EBL models. The downward arrow
represents the 95% upper limit on the
opacity at z = 1.05 derived in A. A. Abdo et
al., Astrophys. J. 723, 1082 (2010).
.
Wednesday, May 8, 13
10
τγγ
Fig. 1. Measurement, at the 68 and 95% confidence levels (including systematic uncertainties
Fig. 1. Measurement,
at the 68 and 95%
added in quadrature), of the opacity tgg from the
best fits(including
to the Fermi data
compared with predicconfidence levels
systematic
tions of EBL models. The plot shows the measureuncertainties added
quadrature),
of the
ment at z ≈in
1, which
is the average redshift
of the
mostthe
constraining
0.5 ≤ z <
opacity τγγ from
best redshift
fits tointerval
the (i.e.,
Fermi
1.6). The Fermi-LAT measurement was derived comdata compared
with
bining
the prediclimits on thetions
best-fit of
EBL EBL
models. The
downward
arrow represents
the 95% upper limit onat
models. The plot
shows
the measurement
the opacity at z = 1.05 derived in (13). For clarity,
z≈1, which is the
average
this figure
shows onlyredshift
a selection ofof
thethe
models we
tested; the
full list is reported
in table
S1. The
EBL
most constraining
redshift
interval
(i.e.,
0.5≲
models of (49), which are not defined for E ≥ 250/
(1 + z) GeV and thus
could not be used, are reported
z < 1.6). The Fermi-LAT
measurement
was
here for completeness.
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
1
z ≈ 1.0
10 -1
2
10
Energy [GeV ]
M. Ackermann, M. Ajello, et al. (Fermi), Science 338, 1190 (2012)
Measurement of Tau with Energy and Redshift
•  We use the composite likelihood in small
energy bins to measure the collective
deviation of the observed spectra from
the intrinsic ones
•  The cut-off moves in z and energy as
expected for EBL absorption (for low
opacity models)
-τγ γ
eText
Ackermann+12
0
1
0.5
0
1
0.5
•  It is difficult to explain this attenuation
with an intrinsic property of BL Lacs
1.  BL Lacs required to evolve across the
z=0.2 barrier
2.  Attenuation change with energy and
redshift cannot be explained by an
intrinsic cut-off that changes from
source to source because of redshift
and blazar sequence effects
Best-fit EBL model!
Best-fit intrinsic cut-off!
0.2<z<0.5
1
Wednesday, May 8, 13
M. Ackermann, M. Ajello, et al. (Fermi), Science 338, 1190 (2012)
Composite Likelihood Results:Text
2
•  A significant steepening in the blazars’ spectra is detected
•  This is consistent with that expected by a ‘minimal’ EBL:
–  i.e. EBL at the level of galaxy counts
–  4 models rejected above 3sigma
•  All the non-rejected models yield a significance of detection of
5.6-5.9 σ
•  The level of EBL is 3-4 times lower than our previous UL (Abdo+10,
ApJ 723, 1082)
EBL Detection
Significance
Model Rejection
Significance
Ackermann+12
10
Wednesday, May 8, 13
Cosmic Gamma-Ray Horizon
Dominguez+13
+
Ackermann+12
Cosmic -ray horizon [TeV]
Domı́nguez+ 11
10
y
r
a
n
i
m
i
l
e
r
P
1
21
4
n
Mk
01
5
n
Mk
Propagating D+11 errors in SED
fits and redshift extrapolation
489
5
200
S
PK
100
304
5
215
S
PK
24
5
+
806
0
S
1E
10
Furniss+ 2013:
3C66A z=0.33-0.41
04
3
+
218 32
1
2
S
1E 101S1
1E
●
ted
c
e
r
cor
A
6
6
3C
66A
13
1
+
553
1
PG
3C
1
10
Wednesday, May 8, 13
2
10 1
Redshift
100
results. The Cherenkov Telescope Array (CTA; The CTA Consortium 2010) is another possible source of constraining events. The
CTA will have a lower threshold energy than current-generation
ground-based instruments and may be able to detect sources at
Mon. Not. R. Astron. Soc. 420, 800–809 (2012)
doi:10.1111/j.1365-2966.2011.20092.x
much higher redshift than currently achieved from the ground. Detections with either of these instruments could potentially shed new
light onfrom
star formation
thegamma-ray
re-ionizationbursts
era. and active galactic nuclei at
The Fermi satellite has detected GeV emission
a numberinof
ABSTRACT
420, 800–809 (2012)
Rudy C. Gilmore
Constraining the near-infrared background
light from Population III stars using highredshift gamma-ray sources
Constraining the near-infrared background
light
from Population
III sources place on the
the detections
of gamma-rays
from several of these
AC K N OW
L EEmission
D G M E Nfrom
T S these primordial stars, particularly
contribution
of Population
III stars togamma-ray
the extragalactic background
light.
stars
using
high-redshift
sources
could be derived from future detections of high-redshift sources
high6.redshift,
z ≳1.5.figure,
We examine
the constraints
that
Figure
As in the previous
but for a cut-off
redshift zr = 9.
redshifted Lyman α emission, can interact with gamma-raysRCG
to produce
electron–positron
pairsbyand
create an
optical depth to the
was supported
during this work
a SISSA
postdoctoral
with the Fermi LAT or future telescopes. In these plots, the axes
fellowship,
W. B.therefore
Atwood, constrain
J. Primack the
andproduction
A. Bouvier of this
propagation
ofand
gamma-ray
emission,
andenergy
the detection
of emission
at and
>10thanks
GeV can
!
of
a
refer
to
the
redshift
highest
observed
photon
E
γ
Rudy
C. Gilmore
for helpful discussions related to this project, and J. Colucci and the
background.
We source.
consider
initial
mass
functions
hypothetical
gamma-ray
Thetwo
source
is then
assumed
to havefor the early stars and use derived spectral energy distributions for each to put
SISSA, via Bonomea 265, 34136 Trieste, Italy
anonymous referee for reading the manuscript and providing useful
a normalization
at lower
energy
such that the
expected
number
of
upper limits
on the
star formation
rate
density
of massive
early
stars from redshifts 6 to 10. Our limits are complementary to those
comments. Some calculations in the paper were performed on the
in the
photon
and near-infrared
above Eγ is 1 [Nbackground
x (>Ehigh ) = 1]
setcounts
on a athigh
flux
by absence
ground-based
TeV-scale
observations
and show
that current data can limit star
SISSA
High-Performance
Computing
Cluster.
of any
background
field.
The
spectrum
of
the
source
is
set
here
to
Accepted 2011 October 27. Received 2011 October 27; in original form 2011 September 1 −1
formation
in theoflate
stages of
less than
Mpc−3 . Our results also show that the total background flux
−2.25,
near the mean
the sources
in re-ionization
Table 1, and thetop-EBL
is 0.5 M⊙ yr
ignored.
Given
these parameters,
the contours
on the plotsless
show
EFER
E N C E Sgalaxies at wavelengths below 1.5 μm.
from
Population
III stars must
be considerably
than thatRfrom
resolved
ABSTRACT
Abdo A. A. et al., 2009, Sci, 323, 1688
Abdo
A. A. et from
al., 2010a,
ApJ, 710,
810
The Fermi satellite has detected GeV
emission
a number
of gamma-ray
bursts and active
A. A.
al., 2010b,the
ApJ,constraints
723, 1082 that the detections of
galactic nuclei at high redshift, z Abdo
! 1.5.
Weet examine
Abel T., Bryan G. L., Norman M. L., 2000, ApJ, 540, 39
gamma-rays from several of these sources
place on the contribution of Population III stars to the
Aguirre A., Schaye J., Theuns T., 2002, ApJ, 576, 1
extragalactic background light. Emission
from these primordial stars, particularly redshifted
Aharonian F. et al., 2006, Nat, 440, 1018
Lyman α emission, can interact with
gamma-rays
to produce
pairs and create
Albert
J. et al., 2008,
Sci, 320,electron–positron
1752
an optical depth to the propagationAtwood
of gamma-ray
emission,
detection of emission at
W. B. et al.,
2009, ApJ,and
697,the
1071
Becker
R. H. et al.,
AJ, 122, 2850 We consider two initial
>10 GeV can therefore constrain the
production
of2001,
this background.
Giammanco
C., 2010,
Mem.
Soc. Astron. Ital.,
81, 460
mass functions for the early starsBeckman
and useJ.,derived
spectral
energy
distributions
for each
to
Bouché N., Lehnert M. D., Aguirre A., Péroux C., Bergeron J., 2007, MNput upper limits on the star formation rate density of massive early stars from redshifts 6 to
RAS, 378, 525
10. Our limits are complementaryBouwens
to thoseR.set
a high near-infrared
background
flux ApJ,
by 670,
J., on
Illingworth
G. D., Franx M.,
Ford H., 2007,
ground-based TeV-scale observations928
and show that current data can limit star formation in
−3
Mpc
. Rev.,
Our 46,
results
the late stages of re-ionization to Breit
less than
0.5 M!
yr−1
G., Wheeler
J. A.,
1934,
Phys.
1087 also show that
Bromm V.,III
Coppi
S., Larson
R. B., 2002, ApJ,
23 that from
the total background flux from Population
starsP. must
be considerably
less564,
than
Bromm1.5
V.,µm.
Loeb A., 2004, New Astron., 9, 353
resolved galaxies at wavelengths below
Brown R. L., Mathews W. G., 1970, ApJ, 160, 939
Cambrésy
L., Reach
W. T., Beichman
C. A., radiation.
Jarrett T. H., 2001, ApJ, 555,
Key words: gamma-ray burst: general
– stars:
Population
III – diffuse
563
Chabrier G., 2003, PASP, 115, 763
Cooray A., Yoshida N., 2004, MNRAS, 351, L71
Domı́nguez A.
et al.,is2011,
MNRAS,
410, 2556
cosmological
impact
therefore
the primary
way of understanding
1 I N T RO D U C T I O N
Dwek E., Krennrich F., 2005, ApJ, 618, 657
the properties of the re-ionization-era universe.
Wednesday,
8, 13
Figure
7. PlotMay
of the
upper bounds on the SFRD in two possible scenarios
Fernandez E. R., Komatsu E., 2006, ApJ, 646, 703
Star Formation Rate Density
5σ
(Madau Plot)
3σ
2σ
Upper bounds on the redshift z = 6 - 10 Pop-III
SFRD in two possible scenarios with future
Fermi GRBs, in the Larson IMF case. The solid
lines show the limits from a GRB with the same
redshift and spectral characteristics of GRB
080916C (z = 4.35), but with a highest energy
observed photon of 30 GeV (160 GeV as
emitted) instead of 13.2 GeV, in combination
with the 5 most constraining z ≳ 2 sources
(Abdo+2010). The dotted lines show a case
with a GRB at z = 7 and a highest energy
observed photon at 15 GeV (120 GeV emitted).
Conclusions
New data on attenuation of gamma rays from blazers
● X-ray + Fermi + ACT SSC fits to 9 blazars (Dominguez+12)
● Fermi data on 150 blazars at z = 0 - 1.6 (Ackermann+12)
now lead to statistically significant measurements of the cosmic
gamma ray horizon and EBL as a function of source redshift
and gamma ray energy.
These new measurements are consistent with recent EBL
calculations based both on multiwavelength observations of
thousands of galaxies and also on semi-analytic models of the
evolving galaxy population. Such comparisons account for all
the light, including that from galaxies too faint to see.
Catching a few high-redshift GRBs with Fermi or low-threshold
atmospheric Cherenkov telescope arrays could provide
important new constraints on the high-redshift star formation
history of the universe.
Happy Birthday Felix Aharonian!
Wednesday, May 8, 13