Date : The 11th of November, 2015.
Speaker : Dr. Genoveva Michea (Subaru Telescope, NAOJ)
Title : High-z sources of Lyman Continuum from the SSA22 field
Abstract:
The escape fraction of Lyman continuum (LyC) is the fractio
n of hydrogen ionizing radiation that escapes from a galaxy
into the intergalactic medium (IGM) and contributes either t
o reionizing the Universe at redshifts z>6 or to keeping it
ionized at lower redshifts. In this talk we will present the
largest to date sample of LyC emitting galaxies at any reds
hift, with 18 Lyman Alpha Emitters (LAEs) and 7 Lyman Break
Galaxies (LBGs), obtained from the SSA22 field with Subaru/S
uprime-Cam. A spatial offset is often detected between the r
est-frame non-ionizing ultraviolet (UV) detection and the Ly
C-emitting substructure or between the LyA emission and LyC.
We show that statistically it is highly unlikely that all L
yC candidates are foreground contaminants. From comparison t
o stellar evolutionary models (SEDs) both LAEs and LBGs host
ing the LyC escape seem to require extremely metal-poor or e
ven metal-free young (zero-age) populations. We further show
that "standard" SED models cannot fully explain the observe
d LyC LAEs colors, and require exotic models instead, with a
top-heavy initial mass function with an average stellar mas
s of ~100 M_sun and the "Lyman limit bump" model which postu
lates an escape of nebular recombination LyC. We find some e
vidence for a positive LyC/LyA correlation, suggesting that
both LyC and LyA escape via a similar mechanism. The LyC emi
ssion seems to be bimodal - stacking non-detections reveals
no significant LyC signal strength. From LyC detections we o
btained estimates of LyC escape fraction of ~20% for LyC LBG
s and ~30% for LyC LAEs, assuming an SMC dust law. From non-
detections we obtain 3 sigma median upper limits on the flux
density ratios as f(LyC)/f(UV)<0.08 from 143 non-LyC LAEs,
and f(LyC)/f(UV)<0.02 from 133 non-LyC LBGs. We will also in
troduce a new Subaru intensive program on the "Cosmic HydrOg
en Reionization Unveiled with Subaru" (CHORUS). The project
will target the 3 central issues of Cosmic reionization: ion
ization sources, history, and topology.


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