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The Subaru Seminar is usually held in Room 104 of the Hilo Base Facility, adjacent to the main lobby. Everyone is welcome to attend. If you are interested in giving a seminar, please contact Subaru seminar organizers (Tadayuki Kodama, Kumiko S. Usuda, Naoyuki Tamura, Tomonori Usuda) by email : sseminar_at_subaru.naoj.org (please change"_at" to @).

January 7, Monday at 10:30 am

" GRB Host Galaxies: General Investigation and Observational Importance for Peculiar Cases "

Jirong Mao (Yukawa Institute for Theoretical Physics, Kyoto University)


Attenuation of gamma-ray burst (GRB) afterglow is one important topic to understand GRB environment and GRB progenitor. (1) As long-duration GRBs are related to star formation, afterglow absorption by the surrounding medium in GRB host galaxy is possible. I apply one galaxy evolution model to investigate some properties of GRB host galaxies. The absorption of GRB X-ray/optical afterglow is also achieved. (2) I introduce the case of "dark" property shown in short-duration GRB afterglow. I stress the observational importance to the host galaxies of dark short GRBs. Some possible explanations to the "dark" property of short GRB afterglow are discussed as well.

" Possible high metallicity environment of GRB 080325 and 100418A "

Tetsuya Hashimoto (TMT-J/NAOJ)


We present two case studies of host galaxies of GRB 080325 and 100418A observed with Subaru telescope. We obtained near-infrared and optical spectra of GRB 080325 and 100418A hosts respectively. The metallicites of the hosts are estimated to be 12+log(O/H)=8.75 and 8.8 (KK04) by using emission-line diagnostics. Although these metallicites are comparable to or below the mass-metallisity relations explored for typical star-forming galaxies at each redshift, these clearly exceed the previously proposed critical metallicity below which GRBs occur, suggesting possible high-metallicity environment around GRBs. Because the single star scenario of GRB (massive single star explosion) requires low metallicity environment, these GRBs do not match up with such model. One possible origin is binary-star merger scenario for long GRBs; GRBs can occur even in high metallicity environment.


Seminars are also held at JAC, CFHT, and IfA.



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