Study on Gamma-Ray Burst host galaxies in the TMT era Tetsuya Hashimoto (NAOJ) 1

Imaginary picture of Gamma-Ray Burst (GRB) –death of massive star– that is, supernova explosion 2

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) brightness GRB B Racusin 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 3

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? 4

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 rapidly rotating progenitor becomes GRB slowly rotating progenitor does not become GRB 5

Metallicity 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 Direct metallicity measurements of GRB host galaxies by spectroscopic observations Modjaz et al 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 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 “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 GRBs Properties of Dark GRB hosts remains a mystery makes it difficult to discover and identify their hosts 7 Jochen Greiner, 14-Oct-2013

Hα [NII]6584 GRB host Dark GRB -Spectroscopic follow up with Subaru – GRB host Hα [NII]6584 Angstrom Whole GRB site South part Relative flux density Hashimoto et al Hashimoto et al in prep. 8

High-metal host!? levesque et al A (z=0.624) DEEP2 Survey (0.4 < z < 1.0) Abraham et al Erb et al (z ～ 2) ★ (KK04) (z=1.78) (dark GRB) ★ ★ GRB site Whole South part critical metallicity Niino+ T. H. et al Hashimoto et al in prep. 9

TMT Era -Complete dark and non-dark GRBs- Kann et al Dark GRB 10

Hatsukade, T.H. et al Search for GRBs occurred 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 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 12

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. 13