Probing ionizing radiation of.

ABSTRACT We show the effectiveness of strong lensing in the characterization of Lyman continuum emission from faint L≲ 0.1 L* star-forming galaxies at redshift ≳3. Past observations of L≳ L* galaxies at redshift ≳3 have provided upper limits of the average escape fraction of ionizing radiation of fesc∼ 5 per cent. Galaxies with relatively high fesc (>10 per cent) seem to be particularly rare at these luminosities; there is therefore the need to explore fainter limits. Before the advent of giant ground-based telescopes, one viable way to probe fesc down to 0.05-0.15 L* was to exploit strong lensing magnification. This is investigated with Monte Carlo simulations that take into account the current observational capabilities. Adopting a lensing cross-section of 10 arcmin2 within which the magnification is higher than 1 (achievable with about four to five galaxy clusters), with a U-band survey depth of 30 (30.5) ( AB, 1σ), it is possible to constrain fesc for z≃ 3 star-forming galaxies down to 15 (10) per cent at 3σ for L < 0.15 L* luminosities. This is particularly interesting if fesc increases at fainter luminosities, as predicted from various H i reionization scenarios and radiation transfer modelling. Ongoing observational programmes on galaxy clusters are discussed and positive prospects for the future are offered, even though from space the Hubble Space Telescope ( HST)/Wide Field Camera 3 (WFC3) instrument represents the only option we have to investigate details of the spatial distribution of the Lyman continuum emission arising from z∼ 2-4 galaxies. [ABSTRACT FROM AUTHOR]