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CTAで切り拓くガンマ線観測的宇宙論（超遠方宇宙）井上進（京大理）withGeV

R. Salvaterra, T. R. Choudhury, A. Ferrara,
B. Ciardi, R. Schneider(MNRAS in press, arXiv:0906.2495)

Fermi

Y. Inoue, M. Kobayashi, T. Totani, Y. Niinou(in prep.)CTA

z~30-6
blazarGRB

submm

ALMAGgamma-ray “absorption”: probe of diffuse radiation fields
1.

tionnnergy

gamma-ray absorption:probe of diffuse radiation fields
γ + γ → e+ + eE εthreshold condition: E ε (1-cos θ )>2 me2c4
σ peak,,=4 me2c4

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

Costamante et al 03

e.g. probe of local IRB throughgamma absorption in TeV blazars

Extragalactic Background Lightblazar

IACT

γVHE

γEBLe+e-

手嶋さんのスライドより

(highest to date)probing local IR background with gamma-ray absorption
HESS observations of TeV blazars @z=0.165, 0.186
Aharonian+ 06 Nat.

• strongly disfavors NIR peakno strong Pop III• close to lower limits from galaxy counts• strongly rules out NIR peakMatsumoto+Sugiyama priv. comm.

EBL constraints at z=0.536
Albert+ 08 Sci.

Eγ(τ=1)MAGIC observation
80-500 GeV
3C279 @z=0.536

close to lower limits from galaxy counts (little missing light)
if “normal” blazar spectra α>1.5

EBL constraints at z=4.35

Abdo+ 09, Sci. 323, 1688

Fermi/LAT detection of GRB 080916C up to 13 GeV without cutoff

slides from T. R. Choudhurydetectability of high-z GRBs by CTA
Abdo+ 09
GRB 080916C
at z=30CTAevrucy
1min itivit EDs ORnes NSAECT C
1hr

GRB 080916C Fermi (z=4.3)
TeV extrapolation, delayed~ 10-9 erg/cm2/s at T~1000s
neglecting EBL absorption,
detectable out to z=30!!!

scosmic reionization epochz>6 current observational frontier
When? early? late? two-epoch?
How?

topology?

What? Pop III? Pop II?
mini-QSOs?
dark matter decay?

So what?
suppression ofdwarf galaxy
formation

Madau 07

Hubble Ultra Deep Field 2009 (HUDF09) with newly installed
WFC3/IRcosmic star formation rate

Bouwens+ arXiv:0912.4263
submitted to Nature

UV flux from observed galaxies:
only ~13% of reionization requirement (with fesc=0.5, C=3, Salpeter IMF)

cosmic star formation rateestimated from GRB rate Kistler+ 09

UV intergalactic radiation field (IRF) at high-z
crucial in cosmic reionization/first star formation era• IRF above Lyman edge ε>13.6 eVreionizes the IGM (feedback on galaxy formation)• IRF below Lyman edge
dissociates H2 molecules (feedback on star formation) ε=11.2-13.6 eV
Lyα pumping (affects HI 21cm emission) ε=10.2 eV

but direct detection impossible!

↑Ly edge

gamma-ray absorption= direct census of diffuse UV below Ly edge (indep. of fesc, C)
gamma-ray “absorption”: probe of diffuse radiation fields

model of cosmic reionization

SI+ arXiv:0906.2495

Choudhury & Ferrara 05, 06, Choudhury 09

parameters ε*II, ε*III, ηesc, λ0IGM

semi-analytical model with Pop III+II stars+QSOs, radiative+chemical feedback
consistent with large set of high-z observations: WMAP, xHI, HUDF NIR counts, etc.

HUDFxHIWMAP3(WMAP5 OK)

SFR

Lyα

Γphotoion

Lyβ

TIGM

LLSreionization
begins z~15
90% z~8
100% z~6γγ absorption attenuation factor

SI+ arXiv:0906.2495

low z model
Kneiske+ 04(high stellar UV)(high UV)

Fermi
CTA, AGIS
5@5appreciable differences in attenuation between z~5-8 at several GeV→ unique, important info on evolution of UV IRF below Ly edge
= direct census of cosmic star formation rate (indep. of fesc, C)appreciable differences in attenuation between z~5-8 at several GeVInoue, M. Kobayashi, Totani, SI+
cosmic star formation rate Y.
in prep.

CAUTION:data at z>6
mostly lower limits
to cosmic SFR

large uncertainties in SFR at z>6
models with low Pop II but high Pop III also possible?

γγ optical depth: comparison

Y. Inoue+, in prep.

huge differences inabsorption!
-> distinguishable
through CTA obs.

まとめ
CTAでGRBはz~30（初代星形成期）でも見える
ガンマ線吸収からhigh-zのdiffuse UVを探る＝宇宙星形成率の（最も？）robustな測定方法
現実的モデルは10-100GeV領域で大きな違い

CTAは観測的宇宙論に本質的な寄与ができる！