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Subaru Seminars are usually held in Room 104 of the Hilo Base Facility, adjacent to the main lobby. Everyone is welcome to attend. If you would like to give a seminar, please contact Subaru seminar organizers (Thayne Currie, Tae-Soo Pyo, Nagayoshi Ohashi) by email : (please change"_at" to @).

March 16, Thursday, 1 pm in 104B

" First Direct Te Method Determinations of Gas-Phase Metal Abundances and Ionization Parameters for high-z Lyα Emitters "

Takashi Kojima

(University of Tokyo)

yα emitters (LAEs) play an important role in the cosmic re-ionization. However, the ionization properties of LAEs are poorly understood. The ionization parameter and gas-phase metallicity are key quantities to understand the ionization properties of LAEs. With deep optical and near-infrared spectroscopy, we estimate the ionization parameter and metallicity of LAEs by the direct electron temperature (Te) method (Kojima et al. 2017). Our sample consists of five typical LAEs at z=1.7-2.3 with log(M*/M_sun)~9.5 and rest-frame Lyα equivalent width of EW_0(Lyα)=30-160A. The direct Te method enables the robust estimates of Te=13,000-14,000 K, metallicity 12+log(O/H)=8.05-8.14, and ionization parameter q_ion=8.1-8.2 cm/s of these LAEs with a typical error of ~10%, excluding the systematic bias that the previous studies cannot remove. Comparing these LAEs to 30 Lyman break galaxies (LBGs) with EW_0(Lyα)~0 on the similar M*, SFR and O/H basis, we have revealed that LAEs have ionization parameters three times higher than those of LBGs based on the direct Te method. With these robust estimates obtained by the direct Te method, we have confirmed that the nature of LAEs is characterized by the high ionization parameter as well as the large Lyα equivalent width.

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