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)

Swift (gamma- and X-ray)

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

time after the burst (s)

brig

htne

ss

GRB 080319BRacusin et al. 2008, Nature

GRB

Afterglow

1 hour 1 day

``Afterglow’’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

Light curve

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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

(e.g., Kistler et al. 2009)

Cosmic star formation history ∝ production rate of GRB

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)

Before massive star explodes, stellar wind carries the rotating momentum (spin angular momentum) of the progenitor away

(single-star explosion scenario) e.g., Woosley & Bloom 2006, Yoon et al. 2006

rapidly rotating progenitor becomes GRB

slowly rotating progenitor does not become GRB

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Met

allic

ity

Brightness of host galaxies

GRBs occur in

Theory + Observation

Low-metallicity environment

超新星のみ ガンマ線バースト + 超新星

Modjaz 他 2008, AJ

Supernova (w/o GRB) GRB+Supernova

7.5

8.0

8.5

9.0

Direct metallicity measurements of GRB host galaxies by spectroscopic observations

Modjaz et al. 2008

It is widely accepted that

star forming activity traced by GRBs is biased toward low-metallicity

However....6

Wanderman & Piran 2010

Small sample of GRB hostsGRB 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

“Dark” GRB (shows unusually optical faint afterglow)

Detection of faint GRB host galaxies at redshifts around 1~2 is not easy even if 8m-class telescope is used

Significant numbers of dark GRBsProperties of Dark GRB hosts remains a mystery

makes it difficult to discover and identify their hosts

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Jochen Greiner, 14-Oct-2013

Hα

[NII]6584

GRB 080325 host

Dark GRB -Spectroscopic follow up with Subaru–

GRB 080325 hostHα

[NII]6584

Angstrom Angstrom6520 65206600 6600

WholeGRB site

South part

Rela

tive

flux

dens

ity

Hashimoto et al. 2010 Hashimoto et al. 2013 in prep.

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High-metal host!?

levesque et al. 2010

100418A(z=0.624)

DEEP2 Survey (0.4 < z < 1.0)Abraham et al. 2004

Erb et al. 2006(z ～ 2)

★(KK0

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080325 (z=1.78)

(dark GRB)

(dark GRB)

★★ GRB site

WholeSouth part

critical metallicity

Niino+ T. H. et al. 2012

Hashimoto et al. 2013 in prep.

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TMT Era -Complete dark and non-dark GRBs-

Kann et al. 2010

Dark GRB

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Hatsukade, T.H. et al. 2012

Search for GRBsoccurred in SF region obscured by dust

“Extreme Case” of obscured star formation is very rare? 11

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)

・ High metallicity environment of dark GRBs

(Graham et al. 2009; Levesque et al. 2010; Hashimoto et al. 2010)

Another origin of GRBs?

・ Many GRB hosts are less massive and low metallicity, But…

Dark GRB 020819 host at redshift=0.41(Jakobsson et al. 2005)Current 8m-class telescope

Metallicity measurement at GRB position is the key to reveal the origin of GRBs

TMT/IFU_spec with AO is best

Redshift ~2

TMT Era

Spectroscopy Spectroscopy

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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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