Speaker
Dr
Ikuru Iwata
(National Astronomical Observatory of Japan)
Description
Ionizing radiation from young star-forming galaxies are thought to be a dominat
source of ionizing background at
z>3 and to have played a primary role in the cosmic reionization. So knowning the
amount of ionizing photons
from galaxies has particular importance on understanding of the cosmic reionization
process. Since ionizing
photons are easily absorbed by intervening neutral hydrogen clouds, direct
observation of ionizing radiation at
z>6 is virtually impossible. Even at z~3 where there is a significant possibility of
relatively transparent line of
sight, very deep observation is required and escape fraction of ionizing photons
remains highly uncertain. Here we
report the results of our searches for Lyman continuum from high-z galaxies through
deep narrow-band imaging.
We made a special filter for Subaru / Suprime-Cam to optimally trace ionizing
radiation from galaxies in the
SSA22 proto-cluster at z=3.1. The unique wide field-of-view of Suprime-Cam enabled us
to search ionizing
photons from ~200 spectroscopically confirmed galaxies. We detected ionizing
radiation for 17 galaxies, and found
that some of them - especially Ly-alpha emitters which are less luminous in
non-ionizing UV compared to Lyman
Break Galaxies - have surprisingly large ionizing to non-ionizing UV radiation
ratios, which are difficult to be
explained with population synthesis models with standard initial mass functions. We
also made another narrow-
band imaging search with VLT / FORS in a blank field and detected three strong Lyman
continuum sources at
z=3.2. This supports the idea that the strong ionizing sources are ubiquitous in the
early universe. We discuss
the implications of these findings on process of the cosmic reionization, as well as
on galaxy formation in the early
universe.
Primary author
Dr
Ikuru Iwata
(National Astronomical Observatory of Japan)
Co-authors
Dr
Akio Inoue
(Osaka Sangyo University)
Dr
Cedric Ledoux
(ESO)
Dr
Denis Burgarella
(Laboratoire d'Astrophysique de Marseille)
Dr
Hisanori Furusawa
(National Astronomical Observatory of Japan)
Dr
Jean-Michel Deharveng
(Laboratoire d'Astrophysique de Marseille)
Dr
Johan Fynbo
(Dark Cosmology Centre)
Mr
Katsuki Kousai
(Tohoku University)
Dr
Masayuki Akiyama
(Tohoku University)
Mr
Niels-Erik Koford
(Dark Cosmology Centre)
Dr
Palle Moller
(ESO)
Dr
Tomoki Hayashino
(Tohoku University)
Prof.
Toru Yamada
(Tohoku University)
Dr
Yuichi Matsuda
(Durham University)
