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Study on Gamma-Ray Burst
host galaxies in the TMT era
Tetsuya Hashimoto (NAOJ)
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Imaginary picture of Gamma-Ray Burst (GRB)
–death of massive star–
that is, supernova explosion
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Gamma-Ray Burst (GRB)
Among the most energetic explosions in the universe,
GRBs are bright flashes of enormous gamma rays that
appear suddenly in the sky and usually last only several to
a few tens of seconds
Light curve
GRB
``Afterglow’’
brightness
The afterglow of a GRB can be
observed in the X-ray, optical,
and near-infrared wavelengths
for several hours to several
days
Afterglows quickly fade after
the burst
Swift
(gamma- and X-ray)
Afterglow
GRB 080319B
Racusin et al. 2008, Nature
1 hour
1 day
time after the burst (s)
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Cosmic star formation history
∝ production rate of GRB
(e.g., Kistler et al. 2009)
Advantages: GRBs are
・bright enough to be detected at redshift > 10
・expected to be observable even if obscured by dust
Gamma Ray is not attenuated by dust
Problem to be solved:
・What kind of galaxies or star forming regions are traced by GRBs?
GRB is really unbiased tracer of cosmic star formation history?
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GRB and metallicity (Theory)
(single-star explosion scenario)
e.g., Woosley & Bloom 2006,
Yoon et al. 2006
Before massive star explodes, stellar wind carries the rotating momentum (spin
angular momentum) of the progenitor away
rapidly rotating
progenitor
becomes GRB
slowly rotating
progenitor does
not become GRB
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Direct metallicity measurements of GRB host
galaxies by spectroscopic observations
Metallicity
9.0
超新星のみ
Supernova
(w/o GRB)
ガンマ線バースト+超新星
GRB+Supernova
Theory + Observation
GRBs occur in
8.5
Low-metallicity
environment
8.0
It is widely accepted that
7.5
Modjaz 他 2008, AJ
Modjaz et al. 2008
Brightness of host galaxies
star forming activity traced
by GRBs is biased toward
low-metallicity
However....
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Small sample of GRB hosts
GRB event rate ~ 1 event / 3 day  totally ~1140 events at the present time
But... ``well explored’’ GRB hosts ~ 50 – 160 (Savaglio et al. 2009, Perley+2013)
This is because majority of GRBs is at redshift = 1~2
Piran 2010
Detection of faint GRB host galaxiesWanderman
at redshifts &
around
1~2 is
not easy even if 8m-class telescope is used
“Dark” GRB (shows unusually optical faint afterglow)
makes it difficult to discover and identify their hosts
Jochen Greiner,
14-Oct-2013
Significant numbers of dark GRBs
Properties of Dark GRB hosts remains a mystery
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Dark GRB -Spectroscopic follow up with Subaru–
GRB site
Whole
South part
Hashimoto et al. 2010
Relative flux density
Hα
Hashimoto et al. 2013 in prep.
GRB 080325 host
[NII]6584
GRB 080325 host
6520
Hα
[NII]6584
Angstrom 6600
6520
Angstrom
6600
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High-metal host!?
Hashimoto et al. 2013 in prep.
(KK04)
Niino+ T. H. et al. 2012
100418A
(z=0.624)
DEEP2 Survey
(0.4 < z < 1.0)
Abraham et al. 2004
080325 (z=1.78)
(dark GRB)
(dark GRB)
★ Whole
★ South part
★ GRB site
critical metallicity
Erb et al. 2006
(z ～ 2)
levesque et al. 2010
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TMT Era
-Complete dark and non-dark GRBs-
Dark GRB
Kann et al. 2010
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Search for GRBs
occurred in SF region obscured by dust
Hatsukade, T.H. et al. 2012
“Extreme Case” of obscured star formation is very rare?
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TMT Era –Origin of GRB–
・GRB production requires low-metallicity environment suggested by theoretical simulations
(MacFadyen& Woosley 1999; Woosley & Heger 2006; Yoon et al. 2006; Niino et al. 2009)
・Many GRB hosts are less massive and low metallicity, But…
・High metallicity environment of dark GRBs
Another origin of GRBs?
(Graham et al. 2009; Levesque et al. 2010; Hashimoto et al. 2010)
Spectroscopy
Spectroscopy
Dark GRB 020819 host at redshift=0.41
(Jakobsson et al. 2005)
Current 8m-class telescope
Redshift ~2
TMT Era
Metallicity measurement at GRB position is the key to reveal the origin of GRBs
TMT/IFU_spec with AO is best
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Summary
Recent studies on missing dark GRBs suggests possible
high-metallicity environment in contrast to low metallicity
prediction by theoretical simulations.
High sensitivity of TMT would promise to complete dark
GRB hosts and clarify the traceability of cosmic star
formation history with GRBs.
TMT/IFU spectroscopy is best suited to understanding the
origin of GRB.
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