「中間」 z~1-5 の系外背景放射光について

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

diffuse extragalactic background radiation at z=0

EBL=extragalacticbackground light:IR-optical-UVfromstars+AGN+others

gamma-ray absorption:probe of diffuse radiation fields

+ → e+ + e-

threshold condition: E (1-cos )>2 me2c4

E

e.g. TeV + 1eV (IR) 100 GeV + 10 eV (UV)

peak ,, =4 me2c4

probe of local IRB from absorption in TeV blazars

Costamante+ 03

e+

e-

EBLVHE

IACT

Extragalactic Background Lightblazar

from M. Teshima

EBL: direct vs indirect measurements

direct source counts absorption

detection lower limit detectionor upper limit or upper limit

faint+diffuse bright sources faint+diffuse

z-integrated z-dependent z-dependent

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

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 observation80-500 GeV3C279 @z=0.536

constraints on EBL at z~0.5-4.5 Abdo+ 10highest energy photons from Fermi blazars+GRBs vs EBL models (=3)

highest EBL model (Stecker+) ruled out

measurement of EBL at z<0.2 Biteau+ (HESS)Gamma 201275000 photons from 7 brightest blazars, 0.03<z<0.19

assume wide variety of intrinsic spectra inc. curvatureEBL template Franceschini, normalization free

consistent withupper limits from previous TeVlower limits from galaxy counts

measurement of EBL at z<1.6Ajello+ (Fermi) Gamma 2012

hard, nonvariable BL Lacs only50 sources each in z=0-0.2, 0.2-0.5, 0.5-1.6assume log-parabolic intrinsic spectraEBL template Franceschini, norm. free

some models ruled out (Stecker+)or disfavored (Kneiske+)

current EBL models

Gilmore+ 12

theory -> predictions -> obs.(understanding <- deductions <- obs.)

cosmic star formation rate -> -dep. luminosity density -> opacity

current EBL models: comparison Gilmore+ 12

z=0

z=1

z=2

current EBL models: comparison Gilmore+ 12

E(=1)

observations candiscriminate amongmodels by differentgroups-But so what?Who cares??

What can we reallylearn about the Universefrom EBL studies?

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

CTA sensitivity: for variable/transient sources

有効面積 ~104 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

high-z blazars with CTA

2FGLJ1504.3+1029 z=1.84

Sol, Zech, Boisson+inc. Y. Inoue (for CTA)to appear in Astropart. Phys.

zmax~ 0.5 now -> ~2.5 with CTA

GRB spectra with CTA: GRB 090902B at z=1.8

S. Inoue,J. Granot,P. O’Brien+ inc.Y. Inoue (for CTA)to appear inAstropart.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

GRB spectra with CTA: GRB 080916C at z=4.3

Mazin+inc.Y. InoueS. Inoue (for CTA)to appear inAstropart.Phys.

GRB スペクトル -> high-z EBL の進化 -> 宇宙星形成史・ QSO活動史

cosmic star formation rate: dispersion at low zKobayashi+ 12

obs’d. dispersionfactor ~3 at z~1-2:different assumedfaint-end slope,Lmin of galaxyluminosity func.

galaxy LF

cosmic star formation rate: from GRB rate

Robertson & Ellis 12(guys from galaxies, not GRBs!)

cosmic star formation rate: from Ly forest

Faucher-Giguere+ 08

hierarchical galaxy formation from Nagashima

cosmic star formation rate: interpretation Nagashima+in prep.growth of structure formation vs decrease of gas supply

peak of CSFR “cosmic gas shortage”

suppression of star formation on sub-Galactic scales:“missing satellites”

Diemand+ 08dark halos inGalaxy formation simulation

Wolf+ 10

critical mass scale ~107Msun

~<106 Lsun

suppression of star formation on sub-Galactic scalesdark 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-dependenceenvironmental dependenceBUT effect only a factor of a few

QSO contribution to UV EBL: HeII Gunn-Peterson effectWorseck+ 11ionization energy:

HeI – 24.6 eV near-simultaneous with H reionization (massive stars)? HeII – 54.4 eV quasars only!

HeII reionized at z~3quasars important for UV EBL!

UV EBL including quasars Faucher-Guigere+ 2011

characteristic energy Erest ~ 72 GeV (2mec2/54.4 eV) Eobs~ 18 GeV (1+z/4)

QSOs not includedin most EBLmodels for rays-> too transparent(exc. Gilmore+ 09)

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