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Exploring the Non-thermal Universe with Gamma Rays Exploring the Non-thermal Universe with Gamma Rays On the occasion of the 60th birthday of Felix Aharonian On the occasion of the 60th birthday of Felix Aharonian Barcelona, November 6 - 9, 2012 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 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. 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. Local EBL Observations Γ ≥ 1.5 Γ ≥ 2/3 Evolution Calculated from Observations Using AEGIS Multiwavelength Data Alberto DomÍnguez, Joel Primack, et al. (MNRAS, 2011) 0.7 ☐° http://aegis.ucolick.org/ 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 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. Domínguez+11 Local Luminosity Density Domínguez+11 Local EBL Observations Domínguez+ 11 vs. Domínguez+11 Propagating errors in SED fits and redshift extrapolation 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) uses the current (WMAP5) 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. 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 Wechsler et al. 2002 • mass accretion history of dark matter halos is~1012 represented by ‘merger trees’ like the one at left 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) 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), 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. 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) 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) 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 .) line types in the key in the left panel. 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 " ersus 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. 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, Felix can make them much harder!) H 1426+428 1ES 0229+200 Gilmore, Somerville, Primack, & Domínguez (2012) 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) Mon. Not. R. Astron. Soc. 000, 1–?? (2011) Printed 31 October 2012 (MN LATEX style file v2.2) Approved by the Fermi Publication Board 31 Oct 2012 Detection of the cosmic -ray horizon from multiwavelength observations of blazars Submitted but not on arXiv A. Domı́nguez1? , J. D. Finke2 , F. Prada3,4,5 , J. R. Primack6 , F. S. Kitaura7 , B. Siana1 , 8,9 10,11 12,13 S. Ciprini , J. Knödlseder and D. Paneque 1 Dept. Physics & Astronomy, University of California, Riverside, CA 92521, USA Naval Research Laboratory, Space Science Division, Code 7653, 4555 Overlook Ave. SW, Washington, DC, 20375 USA 3 Campus of International Excellence UAM+CSIC, Cantoblanco, E-28049 Madrid, Spain 4 Instituto de Fı́sica Teórica, (UAM/CSIC), Universidad Autónoma de Madrid, Cantoblanco, E-28049 Madrid, Spain 5 Instituto de Astrofı́sica de Andalucı́a (CSIC), Glorieta de la Astronomı́a, E-18080 Granada, Spain 6 Department of Physics, University of California, Santa Cruz, CA 95064, USA 7 Leibniz-Institut für Astrophysik (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany 8 INAF, Observatory of Rome, Monte Porzio Catone, Roma, Italy 9 Agenzia Spaziale Italiana (ASI) Science Data Center, I-00044 Frascati (Roma), Italy 10 Institut de Recherche en Astrophysique et Planétologie (CESR), F-31028 Toulouse Cedex 4, France 11 GAHEC, Université de Toulouse, UPS-OMP, IRAP, Toulouse, France 12 Kavli Institute for Particle Astrophysics and Cosmology, SLAC, Stanford University, Stanford, CA 94305, USA 13 Max-Planck-Institut für Physik, D-80805 München, Germany 2 U.S. Presented at the 4th Fermi Symposium in Monterey, CA 31 October 2012 The Detection of the Cosmic γ-ray Horizon ABSTRACT The first statistically significant detection of the cosmic -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) -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 -ray observations of cosmological blazars and -ray bursts. Here, we present synchrotron/synchrotron self-Compton models (SSC) of the spectral energy distributions of 15 blazars based on (almost) simultaneous observa(University California, Riverside) tions from radio up toofthe highest energy -rays taken with the Fermi satellite. These Alberto Domínguez 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 m li e r P PKS 2155-304 z = 0.116 Variability time scale 104 s (fast) y r a n i im l e Pr 1ES 1218+304 z = 0.182 Variability time scale 105 s (slow) Domínguez+12 Cosmic γ-ray Horizon: results Propagating D+11 errors in SED fits and redshift extrapolation There are 4 out of 15 cases where our maximum likelihood methodology could not be applied since the prediction from the synchrotron/SSC model was lower than the detected flux by the Cherenkov telescopes. Two other cases where the statistical uncertainties were too high to set any constraint on E0. Domínguez+12 Published Online in Science 4 Nov 2012 ABSTRACT The light emitted by stars and Reports accreting compact objects through the history of the universe is encoded in the intensity process, a gamma-ray of photonthe of ener- extragalactic background gy E and an EBL photon of energy The Imprint of the Extragalactic E annihilate and create anKnowledge electronlight (EBL). of the EBL is positron pair. This process occurs for Background Light in the Gamma-Ray important head-on collisions when (e.g.) E to understand the nature of star ×E m c ) , where m c is the rest mass energy of the electron. This Spectra of Blazars formation galaxy evolution, but direct introduces an attenuation and in the spectra of gamma-ray sources above a critical M. Ackermann, M. Ajello, * A. Allafort, P. Schady, L. Baldini, J. Ballet, G. measurements of the EBL are limited by gamma-ray energy of E (z Barbiellini, D. Bastieri, R. Bellazzini, R. D. Blandford, E. D. Bloom, A. W. 170(1+z) GeV (7, 8). Borgland, E. Bottacini, A. Bouvier, J. Bregeon, M. Brigida, P. Bruel, The detection of the gamma-ray galactic and other foreground emissions. R. Buehler, * S. Buson, G. A. Caliandro, R. A. Cameron, P. A. Caraveo, E. horizon (i.e., the point beyond which Cavazzuti, C. Cecchi, E. Charles, R. C. G. Chaves, A. Chekhtman, C. C. the emission of gamma-ray sources is Here, we report absorption in the combined spectra of a sample of Cheung, J. Chiang, G. Chiaro,an S. Ciprini, R. Claus, J.feature Cohen-Tanugi,seen strongly attenuated) is one of the priJ. Conrad, S. Cutini, F. D’Ammando, F. de Palma, C. D. mary scientific drivers of the Fermi gamma-ray outA. to a redshift 1.6. This feature is caused by attenuation of Dermer, S. W. Digel, blazars E. do Couto e Silva, Domínguez, P. S. Drell, of A. z ∼ Gamma-ray Space Telescope (9–11). The Imprint of the EBL Drlica-Wagner, C. Favuzzi, S. J. Fegan, W. B. Focke, A. Franckowiak, Y. Several attempts have been made in Fukazawa, S. Funk, P. Fusco, F. Gargano, D. Gasparrini, N. Gehrels, the past but none detected the longgamma rays by the EBL M. atGiroletti, optical to ultraviolet frequencies and allowed us to measure S. Germani, N. Giglietto, F. Giordano, T. Glanzman, G. sought EBL attenuation (12–14). So in Godfrey, I. A. Grenier, J. E. Grove, S. Guiriec, M. Gustafsson, D. far, limits on the EBL density have the EBL flux density in this frequency band. Hadasch, M. Hayashida, E. Hays, M. S. Jackson, T. Jogler, J. been inferred from the absence of abEBL EBL 2,3 2 9,10 2 2 2 2 31 32 2 19,20 2 12 2,35 38,39 2 18 13,14 31 33 34 33 33 11 2 2 14 13,14 6 16 25 13,14 15 13,14 17 2 2 13,14 crit 21 19,29,30 2 2 37 24,20 18 2 15 6 23 26,27,28 13,14 2 2 e 6 2 11 16 19,20 22 5 2 12 9,10 18 4 11 2 2 36,27 2 2 9 2 26,27,40 Kataoka, J. Knödlseder, M. Kuss, J. Lande, S. Larsson, L. Latronico,41 F. Longo,7,8 F. Loparco,13,14 M. N. Lovellette,31 P. Lubrano,19,20 M. N. Mazziotta,14 J. E. McEnery,33,42 J. Mehault,25 P. F. Michelson,2 T. Mizuno,43 C. Monte,13,14 M. E. Monzani,2 A. Morselli,44 I. V. Moskalenko,2 S. Murgia,2 A. Tramacere,45 E. Nuss,25 J. Greiner,4 M. Ohno,46 T. Ohsugi,43 N. Omodei,2 M. Orienti,34 E. Orlando,2 J. F. Ormes,47 D. Paneque,48,2 J. S. Perkins,33,49,50,51 M. Pesce-Rollins,11 F. Piron,25 G. Pivato,10 T. A. Porter,2, 2 S. Rainò,13,14 R. Rando,9,10 M. Razzano,11,12 S. Razzaque,21 A. Reimer,52,2* O. Reimer,52,2 L. C. Reyes,53 S. Ritz,12 A. Rau,4 C. Romoli,10 M. Roth,54 M. Sánchez-Conde,2 D.A. Sanchez,55 J. D. Scargle,56 C. Sgrò,11 E. J. Siskind,57 G. Spandre,11 P. Spinelli,13,14 ukasz Stawarz,46,58 D. J. Suson,59 H. Takahashi,32 T. Tanaka,2 J. G. Thayer,2 D. J. Thompson,33 L. Tibaldo,9,10 M. Tinivella,11 D. F. Torres,16,60 G. Tosti,19,20 E. Troja,33,61 T. L. Usher,2 J. Vandenbroucke,2 V. Vasileiou,25 G. Vianello,2,62 V. Vitale,44,63 A. P. Waite,2 B. L. Winer,64 K. S. Wood,31 M. Wood2 Downloaded from www.sciencemag.org on November 4, 2012 1 7,8 e the Spectra of Blazars sorption features in the spectra of individual blazars (13, 15), distant galaxies with bright gamma-ray emission powered by matter accreting onto central, massive black holes. While this feature is indeed difficult to constrain for a single source, we show that it is detected collectively in the gamma-ray spectra of a sample of blazars as a cutoff that changes amplitude and energy with redshift. We searched for an attenuation of the spectra of blazars in the 1-500 GeV band using the first 46 months of observations of the Large Area Telescope (LAT) on board the Fermi satellite. At these energies gamma rays are absorbed by EBL photons in the optical to UV range. Thanks to the large energy and redshift coverage, Fermi-LAT measures the intrinsic (i.e., unabsorbed) spectrum up to 100 GeV for any blazar at z < 0.2, and up to 15 GeV for any redshift. The LAT has detected > 1000 blazars to date (16). We restricted our search to a subset of 150 blazars of the BL Lacertae (BL Lac) type that are Presented at the 4th Fermi Symposium in Monterey, CA The Imprint of the EBL in the Spectra of Blazars *To whom correspondence should be addressed. E-mail: [email protected] (M.A.); [email protected] (R.B.); [email protected] (A.R.) Affiliations are listed at the end of the paper. The light emitted by stars and accreting compact objects through the history of the universe is encoded in the intensity of the extragalactic background light (EBL). Knowledge of the EBL is important to understand the nature of star formation and galaxy evolution, but direct measurements of the EBL are limited by galactic and other foreground emissions. Here, we report an absorption feature seen in the combined spectra of a sample of gamma-ray blazars out to a redshift of z 1.6. This feature is caused by attenuation of gamma rays by the EBL at optical to ultraviolet frequencies and allowed us to measure the EBL flux density in this frequency band. Marco Ajello1,2, Anita Reimer3, Rolf Buehler1 on behalf of the Fermi-LAT collaboration Analysis Procedure We look for the collective deviation of the spectra of blazars from their intrinsic spectra • We use 46months of P7V6 1-500 GeV data • We define 3 redshift bins with 50 sources each: – z= 0-0.2, 0.2-0.5, 0.5 -1.6 • All BL Lacs are modeled with a LogParabola spectrum • We perform a combined fit where: – The spectra of all sources are fit independently – The spectra of all sources are modified by a common e-b τ(E,z) term • We evaluate 2 cases: 1. Null hypothesis b=0 : there is no EBL 2. Null hypothesis b=1 : the model predictions are correct preliminary Fit to ‘unabsorbed’ data Simulated SEDs Simulated data F(E) absorbed = F(E) int rinsic ⋅ e −b⋅τ mod el 7 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 Best-fit EBL model! • The cut-off moves in z and energy as expected for EBL absorption (for low opacity models) Ackermann+12 • 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 intrinsic cut-off! 1 Composite Likelihood Results: 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 Cosmic Gamma-Ray Horizon Dominguez+12 + Ackermann+12 Cosmic -ray horizon [TeV] Domı́nguez+ 11 y r a n i m i l e r P 101 21 4 n Mk 01 5 n Mk 489 5 200 S PK 100 304 5 215 S PK 24 5 + 806 0 S 1E 10 04 3 + 218 32 1 2 S 1E 101S1 1E 66A C 13 3 1 + 553 1 PG 1 10 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 Star Formation Rate Density 5σ (Madau Plot) 3σ 2σ Upper bounds on the redshift z = 6 - 9 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!