Abstract
The physical properties of Epoch of Reionization (EoR, 6 < z < 9) galaxies are still poorly constrained by observations. Recent HST campaigns such as the Low-Redshift Lyman Continuum Survey (LzLCS) -the largest survey to date probing Lyman continuum (LyC) emission at low redshift- have revealed that compact star formation, high ionization parameters, strong and narrow LyA emission, low dust-attenuation and weak absorption lines seem to characterize the spectra of the strongest LyC emitters.
Unfortunately, we need to rely on indirect indicators for LyC radiation since the opacity of the intergalactic medium prevents us from any direct detection at z > 6. Absorption line measurements have been proved to trace the geometry of neutral and low-ionized gas within the interstellar medium of galaxies and, together with estimates of the dust attenuation, constitute a promising proxy of the LyC escape fraction.
In this talk, I will present an overview on the advantages of using deep, rest-UV spectroscopy to decipher the ionising properties of high-z galaxies. Our methodology, anchored and tested at low-z thanks to the LzLCS, allow us to predict ionizing escape fractions and efficiencies for more than 400 galaxies selected from the VANDELS survey at 3 < z < 5, the last public ESO spectroscopic survey. The ionizing properties of VANDELS galaxies will be then correlated versus diverse galaxy physical properties. Our findings, if extrapolated to the EoR, would imply that the ionizing budget in the EoR was likely dominated by UV-faint, low-mass and dustless galaxies.
