(EBL).
Transcription
(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