Speaker
Description
The escape fraction of Lyman Continuum radiation (f_esc) remains the most uncertain parameter in modeling the epoch of reionization. Depending on its value, and its dependency on galaxy luminosities, different ionization histories and topologies are expected. Photons more energetic than 13.6eV escaping from a galaxy are readily absorbed in the intergalactic medium (IGM) making the f_esc measurement practically impossible at z<3.5.
I will present the results of a new HST study constraining the escape of ionizing radiation in a sample of seven gravitationally lensed galaxies at z~2.4. The lensing magnification allows us to push the measurement of f_esc to faint magnitudes. The galaxies all have Lyman alpha in emission and low dust content (inferred from the slope of the UV continuum), suggestive of high f_esc. We find, however, that our targets are not detected in Lyman continuum, with absolute escape fraction upper limits of ~2%. Our findings disagree with results from previous studies based on local galaxy analogs, suggesting that blindly applying z=0 diagnostics to reionization epoch galaxies may be incorrect.
