Searching for the connection between ionizing-photon escape and the surface density of star formation at z ∼ 3

Abstract

The connection between the escape fraction of ionizing photons (f_(esc)) and star formation rate surface density (Σ_(SFR)) is a key input for reionization models, but remains untested at high redshift. We analyse 35 z ∼ 3 galaxies from the Keck Lyman Continuum Survey (KLCS) covered by deep, rest far-UV spectra of the Lyman continuum (LyC) and high-resolution HST V_(606) imaging, enabling estimates of both f_(esc) and rest-UV sizes. Using Sérsic profile fits to HST images and spectral-energy distribution fits to multiband photometry, we measure effective sizes and SFRs for the galaxies in our sample, and separate the sample into two bins of Σ_(SFR). Based on composite spectra, we estimate 〈f_(esc)〉 for both Σ_(SFR) subsamples, finding no significant difference in 〈f_(esc)〉 between the two. To test the representativeness of the KLCS HST sample and robustness of this result, we attempt to recover the well-established correlation between f_(esc) and Lyα equivalent width. This correlation is not significant within the KLCS HST sample, indicating that the sample is insufficient for correlating f_(esc) and galaxy properties such as Σ_(SFR). We perform stacking simulations using the KLCS parent sample to determine the optimal sample size for robust probes of the f_(esc)-Σ_(SFR) connection to inform future observing programs. For a program with a selection independent of ionizing properties, ≥90 objects are required; for one preferentially observing strongly-leaking LyC sources, ≥58 objects are required. More generally, measuring the connection between f_(esc) and Σ_(SFR) requires a larger, representative sample spanning a wide dynamic range in galaxies properties such as Σ_(SFR).