Exploring the unexpected interplay between Lyman-alpha and C IV emission using spatially resolved imaging
Résumé
The synergy between Lyman-alpha and C IV 1548,50A is among our most promising UV diagnostics for understanding the escape of ionizing photons across all energy levels. Lya probes the properties of low-ionization gas (~13.6 eV), while C IV probes higher-energy levels (>54 eV), corresponding to photons capable of ionizing two hydrogen atoms each. Notably, both HST and JWST observations have uncovered targets with significant C IV emissions in galaxies at redshifts around 5--11. Thus, to disentangle the role of star-forming galaxies in the overall ionizing budget across various energy levels, our models must reproduce both the Lya and C IV emissions. Recent low-z observations of C IV and Lya emitters have revealed intriguing trends: galaxies with substantial C IV emission tend to exhibit larger damped Lyman-alpha absorption, whereas those with prominent Lya emission often display weak or no C IV absorption. This contrasting behavior challenges our current understanding of the interplay between hard ionizing fields and the escape of ionizing photons. It suggests that galaxies with hard ionizing sources may not significantly contribute to reionization due to being embedded in large opaque H I clouds. Here, we propose 25 orbits of HST ACS/SBC observations to spatially resolve the Lya, C IV, and UV emission in a sample of 8 star-forming galaxies at a redshift ~ 0. Four galaxies exhibit strong C IV emission and damped Lya absorption and four have weak C IV emission and dominant Lya emission. The requested observations are essential for improving our understanding of the Lya and C IV synergy and determining the contribution of C IV emitting galaxies to reionization.
