1. blazar 「中間」 z~1-5 の系外背景放射光につ いて GRB z~30-6 井上進 (ICRR/MPP -> MPIK) 協力：長島雅広、小林正和、井上芳幸、戸谷友則ほか GRB what we can (may) learn: - cosmic star formation -> global evolution of cosmic gas - sub-Galactic scale star formation; non-cold dark matter? - HeII reionization, quasar formation+evolution Extragalactic Background Light at “Intermediate” z~1-5 blazar

2. diffuse extragalactic background radiation at z=0 EBL= extragalactic background light: IR-optical-UV from stars+AGN+others

3. gamma-ray absorption: probe of diffuse radiation fields  +  → e + + e - threshold condition: E  (1-cos  )>2 m e 2 c 4 E  e.g. TeV + 1eV (IR) 100 GeV + 10 eV (UV)  peak,, =4 m e 2 c 4 probe of local IRB from  absorption in TeV blazars Costamante+ 03 e+e+ e-e-  EBL  VHE IACT Extragalactic Background Light blazar from M. Teshima

4. EBL: direct vs indirect measurements direct source counts  absorption detection lower limit detection or upper limit faint+diffuse bright sources faint+diffuse z-integrated z-dependent z-dependent

5. constraints on local EBL (z~0) from  -ray absorption Aharonian+ 06 Nat. HESS observations of TeV blazars @z=0.165, 0.186 no strong Pop III disfavors strong near-IR peak close to lower limits from galaxy counts

6. GRB も近いうち見える？ E  (  =1) constraints on EBL at z~0.5 Albert+ 08 Sci. close to lower limits from galaxy counts (little missing light) if “normal” blazar spectra  >1.5 MAGIC observation 80-500 GeV 3C279 @z=0.536

7. constraints on EBL at z~0.5-4.5 Abdo+ 10 highest energy photons from Fermi blazars+GRBs vs EBL models (  =3) highest EBL model (Stecker+) ruled out

8. measurement of EBL at z<0.2 Biteau+ (HESS) Gamma 2012 75000 photons from 7 brightest blazars, 0.03<z<0.19 assume wide variety of intrinsic spectra inc. curvature EBL template Franceschini, normalization free consistent with upper limits from previous TeV lower limits from galaxy counts

9. measurement of EBL at z<1.6 Ajello+ (Fermi) Gamma 2012 hard, nonvariable BL Lacs only 50 sources each in z=0-0.2, 0.2-0.5, 0.5-1.6 assume log-parabolic intrinsic spectra EBL template Franceschini, norm. free some models ruled out (Stecker+) or disfavored (Kneiske+)

10. current EBL models Gilmore+ 12 theory -> predictions -> obs. (understanding <- deductions <- obs.) cosmic star formation rate -> -dep. luminosity density ->  opacity

11. current EBL models: comparison Gilmore+ 12 z=0 z=1 z=2

12. current EBL models: comparison Gilmore+ 12 E  (  =1) observations can discriminate among models by different groups- But so what? Who cares?? What can we really learn about the Universe from EBL studies?

13. CTA sensitivity: for steady sources Funk & Hinton, arXiv:1205.0832 現行チェレンコフ望遠鏡より格段に感度向上 エネルギー閾値の有意な低減 -> より high-z の天体、 GeV-TeV 間感度ギャップの改善

14. CTA sensitivity: for variable/transient sources 有効面積 ~10 4 x LAT@30GeV 短時間積分では圧倒的感度 高速指向性能 ~180deg/20sec (LST; 20 GeV-1TeV) -> 高速変動天体・突発天体に対して強力 Funk & Hinton, arXiv:1205.0832

15. high-z blazars with CTA 2FGLJ1504.3+1029 z=1.84 Sol, Zech, Boisson+ inc. Y. Inoue (for CTA) to appear in Astropart. Phys. z max ~ 0.5 now -> ~2.5 with CTA

16. GRB spectra with CTA: GRB 090902B at z=1.8 S. Inoue, J. Granot, P. O’Brien+ inc. Y. Inoue (for CTA) to appear in Astropart. Phys. 高い光子統計 -> 詳細スペクトル -> EBL 測定 -> 詳細時間変動 -> EBL 吸収と内部 cutoff （ e.g. 内部  吸収）の識別 系外背景光 (EBL) との  → e + e - 吸収 による cutoff

17. GRB spectra with CTA: GRB 080916C at z=4.3 Mazin+ inc. Y. Inoue S. Inoue (for CTA) to appear in Astropart. Phys. GRB スペクトル -> high-z EBL の進化 -> 宇宙星形成史・ QSO 活動 史

18. cosmic star formation rate: dispersion at low z Kobayashi+ 12 obs’d. dispersion factor ~3 at z~1-2: different assumed faint-end slope, L min of galaxy luminosity func. galaxy LF

19. cosmic star formation rate: from GRB rate estimated from GRB rate Robertson & Ellis 12 (guys from galaxies, not GRBs!)

20. cosmic star formation rate: from Ly  forest estimated from GRB rate Faucher-Giguere+ 08

21. hierarchical galaxy formation estimated from GRB rate from Nagashima

22. cosmic star formation rate: interpretation estimated from GRB rate Nagashima+ in prep. growth of structure formation vs decrease of gas supply peak of CSFR “cosmic gas shortage”

23. suppression of star formation on sub-Galactic scales: “missing satellites” high-velocity clouds = gas tidally stripped from accreting dark-matter halos? Diemand+ 08 dark halos in Galaxy formation simulation Blitz+ 99 Connors+ 06 dark matter/power spectrum on sub-galactic scales Wolf+ 10 critical mass scale ~10 7 M sun ~<10 6 L sun

24. suppression of star formation on sub-Galactic scales estimated from GRB rate potential problems with CDM on sub-galactic scales: - overproduction of satellites - over-cuspy cores - too compact disk galaxies dark matter solutions: warm dark matter? nontrivial power spectrum? astrophysical solutions: feedback heating/expulsion by SN? AGN? UV background? tidal disruption? WDM simulation Polisensky & Ricotti 11 star formation on small scales -> reflected in EBL: z-dependence environmental dependence BUT effect only a factor of a few

25. QSO contribution to UV EBL: HeII Gunn-Peterson effect Worseck+ 11 ionization energy: HeI – 24.6 eV near-simultaneous with H reionization (massive stars)? HeII – 54.4 eV quasars only! HeII reionized at z~3 quasars important for UV EBL!

26. UV EBL including quasars Faucher-Guigere+ 2011 characteristic energy E rest ~ 72 GeV (2m e c 2 /54.4 eV) E obs ~ 18 GeV (1+z/4) QSOs not included in most EBL models for  rays -> too transparent (exc. Gilmore+ 09)

27. summary - ガンマ線吸収を用いた EBL 探査は近年大きく進歩 今後 MAGIC 、 CTA でさらに CTA で blazar は z~<2 、 GRB は z~<4 (7?) まで - z~<5 の EBL について、個々のモデル予測は多数あり が、観測から何が本質的に理解できるのか、議論が不足 - 宇宙星形成史について、直接観測と相補的な測定 宇宙全体でのガスの熱的進化の情報 - sub-Galactic scale での星形成（の抑制）について示唆も？ astrophysical feedback or non-cold dark matter - z>~3-4 では quasar も重要な寄与 考慮すればより opaque なはず 銀河間 HeII の再電離、 quasar 進化・形成について重要な情報 これからより定量化します