Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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) 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) 3 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? 4 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 5 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.... 6 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 7 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 8 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 9 TMT Era -Complete dark and non-dark GRBs- Dark GRB Kann et al. 2010 10 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? 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) ・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 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