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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 (Tomonori Usuda, Kumiko S. Usuda, Masayuki Akiyama) by email : (please change"_at" to @).

May 18, Friday at 11:00 am

" Lyman Alpha Emitters in the Hierarchically Clustering Galaxy Formation "

Masakazu Kobayashi

(Kyoto University)

We present a new theoretical model for the luminosity functions (LFs) of Lyman alpha (Lya) emitting galaxies in the framework of hierarchical galaxy formation. We extend a semi-analytic model of galaxy formation which reproduces a number of observations for local galaxies, without changing the original model parameters but introducing just a few new physically-motivated parameters to describe the escape fraction of Lya photons from host galaxies (fesc). Though a previous study using a semi-analytic model simply assumed a constant and universal value of fesc, we introduce two new effects on fesc: extinction by interstellar dust and effect of galactic-scale outflow induced as a feedback of star formation. It is found that the new model nicely reproduces all the observational Lya LFs of the Lya emitters (LAEs) at different redshifts. Our model predicts that galaxies with strong outflows are dominant in the observed LFs with fesc ~ 1, which is consistent with available observational estimates of outflow and fesc, and in contrast to the universal fesc model that requires fesc << 1. We then apply our model to estimate the ionization fraction of the universe at z > 6, and find that the IGM transmission to the Lya emission is less than unity at z ~ 6, consistent with the recent constraints by other methods.

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