Insights into the reionization epoch from cosmic-noon-CIV emitters in the VANDELS survey

TL;DR

This study investigates C IV emitting galaxies at cosmic noon ($z\,\sim\,3$) using the VANDELS survey, revealing their potential as analogs of reionizers due to their high photon production and possible large escape fractions.

Contribution

It identifies and characterizes C IV emitters at $z\sim 3$, linking their properties to potential reionization sources, which was not previously established.

Findings

C IV emitters have high photon production efficiency.

They likely have large escape fractions of ionizing photons.

These galaxies are promising analogs of cosmic reionizers.

Abstract

Recently, intense emission from nebular C III] and C IV emission lines have been observed in galaxies in the epoch of reionization ($z>6$) and have been proposed as the prime way of measuring their redshift and studying their stellar populations. These galaxies might represent the best examples of cosmic reionizers, as suggested by recent low-z observations of Lyman Continuum emitting galaxies, but it is hard to directly study the production and escape of ionizing photons at such high redshifts. The ESO spectroscopic public survey VANDELS offers the unique opportunity to find rare examples of such galaxies at cosmic noon ($z\sim 3$), thanks to the ultra deep observations available. We have selected a sample of 39 galaxies showing C IV emission, whose origin (after a careful comparison to photoionization models) can be ascribed to star formation and not to AGN. By using a multi-wavelength approach, we determine their physical properties including metallicity and ionization parameter and compare them to the properties of the parent population to understand what are the ingredients that could characterize the analogs of the cosmic reionizers. We find that C IV emitters are galaxies with high photons production efficiency and there are strong indications that they might have also large escape fraction: given the visibility of C IV in the epoch of reionization this could become the best tool to pinpoint the cosmic reioinzers.