The ionizing photon production efficiency of star-forming galaxies at z∼ 4-10

Investigating the ionizing emission of star-forming galaxies and the escape fraction of ionizing photons is critical to understanding their contribution to reionization and their impact on the surrounding environment. The number of ionizing photons available to reionize the intergalactic medium (IGM) depends on not only the abundance of galaxies but also their efficiency in producing ionizing photons ( This quantity is thus fundamental to quantify the role of faint versus bright sources in driving this process, as we must assess their relative contribution to the total ionizing emissivity. Our goal is to estimate the using Balmer lines (Hα or Hβ) in a sample of galaxies at $4≤ z ≤ 10$ selected from different JWST spectroscopic surveys. We aim to determine the redshift evolution of and the relation of with the physical properties of the galaxies. We used the available HST and JWST photometry to perform a spectral energy distribution (SED) fitting in the sample to determine their physical properties and relate them with We used the BAGPIPES code for the SED fitting and assumed a delayed exponential model for the star formation history. We used the NIRSpec spectra from prism or grating configurations to estimate Balmer luminosities, and then constrained values after dust correction. We find a mean value of 10^25.22Hz erg^-1 for in the sample with an observed scatter of 0.42dex. We find an increase in the median values of with redshift from 10^25.09Hz erg^-1 at z∼4.18 to 10^25.28Hz erg^-1 at z∼7.14 confirming the redshift evolution of found in other studies. Regarding the relation between and physical properties, we find a decrease in with increasing stellar mass, indicating that low-mass galaxies are efficient producers of ionizing photons. We also find an increase in with increasing specific star formation rate (sSFR) and increasing UV absolute magnitude. This indicates that faint galaxies and galaxies with high sSFR are also efficient producers. We also investigated the relation of with the rest-frame equivalent width (EW) of OIII λ5007 and find that galaxies with the higher EW( OIII λ5007) are more efficient producers of ionizing photons, with the best fit leading to the relation log( OIII . Similarly, we find that galaxies with higher O32= OIII λ5007/OIIλλ3727,3729 and lower gas-phase metallicities (based on the R23=($ O III λλ$4959,5007+$ O II λλ$3727,3729)/Hβ calibration) show higher values.