| Precise if your presentation is oral or a poster : | oral |
| Title of your presentation : | The Lyman Continuum Escape Fraction at Moderate Redshift |
| Abstract |
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Massive starbursts may have played a dominant role in the reionization of the Universe. Their contribution depends in part upon the fraction of ionizing radiation that escapes from the intrinsic opacity of galaxies below the Lyman limit. Current surveys suggest that the escape fraction is low in all but 15-25% of galaxies, even among young starbursts. Direct measurement of the escape fraction, f_esc, is impossible at the epoch of reionization, because intervening absorbers make the IGM opaque to Lyman continuum photons. Instead, f_esc must be measured at lower redshifts in objects that are analogous to the galaxies responsible for reionization. Targeting redshifts near unity provides a substantial population of such sources, and allows extremely strong constraints to be placed on f_esc. We present the most recent results of a comprehensive HST survey to measure or limit the value of f_esc in starbursts near z=1. We have obtained far-ultraviolet imaging of the Hubble Deep Field, the Ultradeep Field, and a target sample of z=1.3 starburts, using the Solar Blind Channel (SBC) of the ACS onboard HST. The data constrains the value of relative escape fraction (f_750/f_1500) to be at most 5% in luminous starbursts at z=1.3. The wider survey also shows that the escape fraction does not rise significantly in less luminous objects. Our latest survey uses SBC spectroscopy of z=0.7 galaxies to search for rare, high f_esc objects, and we will present the intial results for observations obtained in February 2008. |
