Oral Presentation
Escape fraction of extreme emission-line galaxies at z~0.8
Presenter: Emi Fujitani (Nagoya University)
Cosmic reionization is the epoch during which ultraviolet photons that escape from the early luminous sources ionized the neutral hydrogen gas and, eventually, the entire intergalactic medium in the universe. It is vital to investigate how early galaxies emitted ionizing photons so as to understand the reionization process. However, directly observations of the ionizing photons during reionization is impossible because of the absorption by the intervening intergalactic gas. In this study, we focus on galaxies at z~0.8 that show extremely strong emission lines discovered by Subaru/HSC-SSP. They offer good laboratories to investigate galaxies in cosmic reionization and are considered to be low-redshift analogs of sources responsible for this age. We selected six extremely bright sources in z-band and obtained deep spectroscopy using VLT/X-shooter to measure emission line fluxes from rest-frame UV to NIR. Five of these six objects were star-forming galaxies, and one was classified as an AGN. We reproduced the observed emission line flux ratios for the five star-forming galaxies using the photoionization simulation code Cloudy. The high [OIII]5007/[OII]3727 and MgII 2796, 2803 doublet lines suggest a high escape fraction (~10% or higher). We considered not only the physical properties of ionized gas but also the finite escape fraction and the geometry of the HII region as parameters in the calculations. We report the gas's physical state, the ionization spectrum's intensity, and the conditions of escape fraction based on the comparisons between the observations and models.
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