Transcript z~1-5の背景放射光について

「中間」 z~1-5の系外背景放射光につ
Extragalactic Backgroundいて
Light at “Intermediate” z~1-5
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
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
GRB
blazar
diffuse extragalactic background radiation at z=0
EBL=
extragalactic
background light:
IR-optical-UV
from
stars+AGN+others
gamma-ray absorption:
probe of diffuse radiation fields
g + g → e+ + eE e
threshold condition: E e (1-cos q )>2 me2c4
s peak
,,
=4 me2c4
Costamante+ 03
e.g. TeV + 1eV (IR)
100 GeV + 10 eV (UV)
blazar
probe of local IRB from
gg absorption in TeV blazars
Extragalactic Background Light
IACT
gVHE
gEBL
e+
e-
from M. Teshima
EBL: direct vs indirect measurements
direct
source counts
g absorption
detection
or upper limit
lower limit
detection
or upper limit
faint+diffuse
bright sources
faint+diffuse
z-integrated
z-dependent
z-dependent
constraints on local EBL (z~0) from g-ray absorption
HESS observations of TeV blazars @z=0.165, 0.186
Aharonian+ 06 Nat.
• disfavors strong near-IR peak no strong Pop III
• close to lower limits from galaxy counts
constraints on EBL at z~0.5
Albert+ 08 Sci.
Eg(=1)
MAGIC observation
80-500 GeV
3C279 @z=0.536
close to lower limits from galaxy counts (little missing light)
if “normal” blazar spectra G>1.5
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
measurement of EBL at z<0.2
Biteau+ (HESS)
75000 photons from 7 brightest blazars, 0.03<z<0.19 Gamma 2012
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
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+)
current EBL models
theory -> predictions -> obs.
(understanding <- deductions <- obs.)
cosmic star formation rate -> l-dep. luminosity density -> gg opacity
Gilmore+ 12
current EBL models: comparison
z=0
z=1
z=2
Gilmore+ 12
current EBL models: comparison
Gilmore+ 12
observations can
discriminate among
models by different
groupsBut so what?
Who cares??
What can we really
learn about the Universe
from EBL studies?
Eg(=1)
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
Funk & Hinton, arXiv:1205.0832
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
Sol, Zech, Boisson+
inc. Y. Inoue (for CTA)
to appear in Astropart. Phys.
high-z blazars with CTA
2FGLJ1504.3+1029
z=1.84
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 in
Astropart.
Phys.
系外背景光 (EBL)
とのgg → e+e-吸収
によるcutoff
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gg吸収）の識別
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
cosmic star formation rate: dispersion at low z
Kobayashi+ 12
obs’d. dispersion
factor ~3 at z~1-2:
different assumed
faint-end slope,
Lmin of galaxy
luminosity func.
galaxy LF
cosmic star formation rate: from GRB rate
Robertson & Ellis 12
(guys from galaxies,
not GRBs!)
cosmic star formation rate: from Lya forest
Faucher-Giguere+ 08
hierarchical galaxy formation
from Nagashima
cosmic star formation rate: interpretation
growth of structure formation vs decrease of gas supply
peak of CSFR “cosmic gas shortage”
Nagashima+
in prep.
suppression of star formation on sub-Galactic scales:
“missing satellites”
Wolf+ 10
Diemand+ 08
dark halos in
Galaxy formation simulation
critical mass scale ~107Msun
~<106 Lsun
suppression of star formation on sub-Galactic scales
astrophysical solutions:
feedback heating/expulsion by
SN? AGN? UV background?
tidal disruption?
dark matter solutions:
warm dark matter?
nontrivial power spectrum?
star formation on small scales ->
reflected in EBL:
z-dependence
environmental dependence
BUT effect only a factor of a few
WDM simulation Polisensky & Ricotti 11
QSO contribution to UV EBL: HeII Gunn-Peterson effect
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!
Worseck+ 11
UV EBL including quasars
Faucher-Guigere+ 2011
characteristic energy Erest ~ 72 GeV (2mec2/54.4 eV)
Eobs~ 18 GeV (1+z/4)
QSOs not included
in most EBL
models for g 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