現在の位置 : TOPページ談話会案内2015年度 > 第1431回 天文学教室談話会

第1431回 天文学教室談話会

日時

2015年11月6日(水) 15:00

場所

合同C棟2階多目的室

講演者

Genoveva Micheva(国立天文台 ハワイ観測所)

題目

High-z sources of Lyman Continuum from the SSA22 field

要旨


The escape fraction of Lyman continuum (LyC) is the fraction of hydrogen ionizing radiation that escapes from a galaxy into the intergalactic medium (IGM) and contributes either to 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 redshift, with 18 Lyman Alpha Emitters (LAEs) and 7 Lyman Break Galaxies (LBGs), obtained from the SSA22 field with Subaru/Suprime-Cam. A spatial offset is often detected between the rest-frame non-ionizing ultraviolet (UV) detection and the LyC-emitting substructure or between the LyA emission and LyC. We show that statistically it is highly unlikely that all LyC candidates are foreground contaminants. From comparison to stellar evolutionary models (SEDs) both LAEs and LBGs hosting the LyC escape seem to require extremely metal-poor or even metal-free young (zero-age) populations. We further show that "standard" SED models cannot fully explain the observed LyC LAEs colors, and require exotic models instead, with a top-heavy initial mass function with an average stellar mass of ~100 M_sun and the "Lyman limit bump" model which postulates an escape of nebular recombination LyC. We find some evidence for a positive LyC/LyA correlation, suggesting that both LyC and LyA escape via a similar mechanism. The LyC emission seems to be bimodal - stacking non-detections reveals no significant LyC signal strength. From LyC detections we obtained estimates of LyC escape fraction of ~20% for LyC LBGs 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 introduce a new Subaru intensive program on the "Cosmic HydrOgen Reionization Unveiled with Subaru" (CHORUS). The project will target the 3 central issues of Cosmic reionization: ionization sources, history, and topology.

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【The Colloquium Committee in 2015】
Kenji Toma (toma<at>astr.tohoku.ac.jp)
Yurina Mizuno
Kohei Miyazawa
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