The Extragalactic Background Light: Connecting Classical and High Energy Astronomy

Transcription

1 The Extragalactic Background Light: Connecting Classical and High Energy Astronomy Alberto Domínguez (Clemson University, South Carolina) Collaborators: Joel Primack, Marco Ajello, Francisco Prada, Justin Finke Mainly based on the review article Domínguez & Primack (2015), Reports on Progress in Physics, in prep. and also partly on behalf of the Fermi collaboration Domínguez, Primack, Bell, Scientific American, 312, 6, June 2015 (Domínguez et al. 2013, ApJ, 770, 77 & Ackermann et al in preparation) Garching bei München, Germany, June 1-3, 2015

2 Diffuse extragalactic backgrounds Scientific American, 312, 6, June 2015 From Genzel's 2013 Jerusalem Winter School The EBL is the accumulated diffuse light produced by star formation processes and accreting black holes over the history of the Univere from the UV to the far-ir. It contains fundamental information about galaxy evolution, cosmology, and it is essential for the full energy balance of the Universe.

3 The local spectral energy distribution of the EBL Domínguez & Primack, 15 in prep. UV optical near-ir mid-ir far-ir M31 view from the UV to the far-ir, Credit: NASA & ESA

4 EBL models Semi-analytical (e.g. Gilmore+ 12, Inoue+ 13) Direct galaxy observations (Luminosity functions) Over redshift (e.g. Domínguez+ 11, Stecker+ 12, Helgason+ 12) Observational Cosmic star-formation rate (e.g. Kneiske+ 10, Finke+ 10, Khaire+ 14) Mainly local (e.g. Stecker+ 06, Franceschini+ 08)

5 Type i: Forward evolution Examples of Λ Cold Dark Matter merger trees from Wechsler+ 02 Slide by Joel Primack Our SAMs are based on Monte Carlo realizations of dark matter halo mergers histories calculated using the modified and extended Press-Schechter methods.

6 Type iv: Direct galaxy observations over redshift Data from the AEGIS collaboration, see Newman+ 13 EGS field 0.7 sq. deg. Total: 5986 galaxies DEEP2 spectroscopic redshift: 4376 galaxies Photometric redshift with mean error less than 0.1: 1610 galaxies

7 Type iv: Direct galaxy observations over redshift Galaxy Spectral Energy Distributions (SEDs) SWIRE template library, Polletta+ 07 Galaxy luminosity function rest-frame K-band, Cirasuolo+ 10 Galaxy SED-type fractions, this work SED of the EBL

8 Local EBL: Data and Models Domínguez & Primack, 15 in prep.

9 Local EBL: Data and Models Domínguez & Primack, 15 in prep.

10 Local EBL: Data and Models Conclusion 1: The EBL contains a bolometric intensity between 50 and 70 nw/m2/sr (this is, about 5% of the CMB intensity). Conclusion 2: Local galaxies typically have E_FIR/E_opt 0.3, while the EBL has E_FIR/E_opt = 1-2. Hence most highredshift radiation was emitted in the far IR. Domínguez & Primack, 15 in prep.

11 EBL evolution with redshift Domínguez & Primack, 15 in prep.

12 EBL evolution with redshift Domínguez & Primack, 15 in prep. EBL models strongly diverge at high redshift

13 Improving the EBL modeling with galaxy surveys Fields by Guillermo Barro GOODS-N GOODS-S EGS COSMOS Credit: ESA / AOES UDS

14 Gamma-Ray Attenuation Scientific American, 312, 6, June 2015

15 Gamma-Ray Attenuation Without EBL: intrinsic With EBL: observed Interaction angle Distance (cosmology) Cross section EBL photon density evolution (cosmology)

16 Local EBL: γ-ray data Different Differentmethodologies methodologiesto toestimate estimatethe theintrinsic intrinsicspectrum: spectrum: --No Nointrinsic intrinsiccurvature curvaturethat thatleads leadsto toupper upperlimits limits(e.g. (e.g.aharonian+ Aharonian+06; 06; Mazin Mazin& &Raue, Raue,07; 07;Albert+ Albert+08) 08) --Extrapolating Extrapolatingthe theunattenuated unattenuatedfermi Fermispectra spectrausing usingdifferent differentassumptions assumptions(e.g. (e.g. Georganopoulos+ Georganopoulos+2010; 2010;Orr+ Orr+2011; 2011;Meyer+ Meyer+2012; 2012;Sánchez+ Sánchez+2013) 2013) --Stacking Stackingof offermi Fermispectra spectra(e.g. (e.g.ackermann+ Ackermann+2012) 2012) --TeV TeVstatistical statisticalanalysis analysis(e.g. (e.g. Abramowski+ Abramowski+2013; 2013;Sinha+ Sinha+2014; 2014;Biteau+ Biteau+2015) 2015) --Using Usingbroad-band broad-bandphotometry photometryfrom fromradio/optical/x-rays radio/optical/x-raysto tofermi/cherenkov Fermi/Cherenkov energies energies(domínguez+ (Domínguez+13) 13)

17 Local EBL: γ-ray data Domínguez & Primack, 15 in prep.

18 Sample and Synchrotron Self-Compton Models Blazars: AGNs emitting at all wavelength with energetic jets pointing towards us. Emission described by homogeneous synchrotron/synchrotron-self Compton model. VHE region 30 GeV<E<30 TeV Quasi-simultaneous multiwavelength catalog of 15 BL Lacs (based on the compilation by Zhang et al. 2012).

19 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 PKS z = Variability time scale 104 s (fast) Domínguez+ 13 on behalf of the Fermi collaboration Maximum likelihood technique with three EBL-model independent conditions: 1.- The optical depth is lower than 1 at E = 0.03 TeV. 2.- The optical depth is lower than the optical depth calculated from the EBL upper limits from Mazin & Raue, 07; especially 1 < τ < UL(z) at E = 30 TeV. 3.- The polynomial is monotonically increasing with the energy.

20 Gamma-Ray Attenuation The cosmic gamma-ray horizon (CGRH) is by definition the energy E0 as a function of redshift at which the optical depth due to EBL is unity. The Themeasurement measurementofofthe thecgrh CGRHisisaaprimary primaryscientific scientificgoal goalofofthe thefermi FermiGamma-Ray Gamma-RayTelescope Telescope (Hartmann (Hartmann07; 07;Stecker Stecker07; 07;Kashlinsky Kashlinsky&&Band Band07) 07) Abdo+ 10 Albert+ 08 Gilmore+ 12

21 Cosmic γ-ray Horizon: Results Domínguez+ 13 on behalf of the Fermi collaboration 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 large to set any constraint on E0.

22 Cosmic γ-ray Horizon: Results Conclusion Conclusion3:3:Constrains Constrainscontribution contributionfrom fromlight lightthat thatescapes escapes totogalaxy galaxysurveys surveysor orany anyother otherpotential potentialcontribution contribution Domínguez+ 13 on behalf of the Fermi collaboration 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 large to set any constraint on E0.

23 Cosmic γ-ray Horizon: Results Domínguez+ 13 on behalf of the Fermi collaboration Less attenuating More attenuating EBL model Rejection Kneiske+ 04 Best Fit 1.62σ Stecker+ 06 Baseline 6.37σ Franceschini σ Kneiske & Dole σ Finke σ Domínguez σ Gilmore+ 12 Fiducial 0.25σ Helgason σ Inoue+ 13 Baseline 2.12σ Khaire+ 15 LMC2 1.27σ Preliminary Preliminary data courtesy of Marco Ajello

24 Cosmological Dependence: Assumed flat ΛCDM H0 = km/s/mpc Statistical uncertainties Domínguez & Prada, 13 Methodology theoretically explored by Blanch & Martínez 05 Multiple paths to independent determinations of the Hubble constant are needed in order to access and control systematic uncertainties Systematic uncertainties

25 2FHL Catalog: Preliminary Numbers Analysis focused in the energy range 50 GeV 2 TeV: More than 6 years of data Pass 8 Position accuracy of 2 arcmin (68% uncertainty) Median source flux of approximately 1e-11 erg/cm^2/s Detections: These numbers are not definitive since they depend on IRFs and diffuse emission model, which are subject to change Around 350 sources 84 detected by ACTs (TeVCat) 238 detected in 1FHL (3 years, up to 500 GeV) 300 detected in 3FGL (4 years, up to 300 GeV) Around 35 brand new sources About 10% of the sources are of Galactic type Bottom line: 270 sources not in TeVCat, 130 not in 1FHL, and 60 not in the 3FGL

26 2FHL Catalog Preliminary Preliminary Preliminary

27 Summary 1.- Independent methodologies converge within a factor 2 or better in the local EBL intensity from the UV to the mid-ir. However, the far-ir and the EBL evolution is still largely unknown. 2.- The CGRH detection is compatible with the recent EBL direct detection in the optical, galaxy counts, and upper limits from gamma-ray attenuation. This constrains the contribution to the low redshift EBL from faint or high redshift galaxies that escape to current galaxy surveys and any other potential contribution. 3.- The detection of the CGRH allows us to derive the expansion rate of the Universe (the Hubble constant) from a novel technique using γ-ray attenuation, whose value is compatible with other rather mature techniques. H0 = km/s/mpc 4.- The cosmological parameters Ωm and w cannot be constrained with current data. 5.- The publication of the Second Fermi catalog of hard sources is imminent.

28 Summary n e e w t e s b e i t y i g n r u e n m y m f S o o c s t t n o e L r e! l f dif sentia sults s e e r s y g i a n t i t S i. c. n ex o o s g n i! m d o e c tu n 1.- Independent methodologies converge within a factor 2 or better in the local EBL intensity from the UV to the mid-ir. However, the far-ir and the EBL evolution is still largely unknown. 2.- The CGRH detection is compatible with the recent EBL direct detection in the optical, galaxy counts, and upper limits from gamma-ray attenuation. This constrains the contribution to the low redshift EBL from faint or high redshift galaxies that escape to current galaxy surveys and any other potential contribution. 3.- The detection of the CGRH allows us to derive the expansion rate of the Universe (the Hubble constant) from a novel technique using γ-ray attenuation, whose value is compatible with other rather mature techniques. H0 = km/s/mpc 4.- The cosmological parameters Ωm and w cannot be constrained with current data. 5.- The publication of the Second Fermi catalog of hard sources is imminent.