The impact of nebular emission on the broadband fluxes of high-redshift galaxies

TL;DR

This paper evaluates how nebular emission significantly affects broadband flux measurements of high-redshift galaxies, emphasizing the importance of including nebular contributions for accurate interpretation of early galaxy properties.

Contribution

It provides a detailed analysis of nebular emission effects on broadband fluxes across various filters and redshifts, highlighting the need to incorporate nebular components in galaxy models.

Findings

Nebular emission can significantly influence broadband fluxes at high redshifts.

Ignoring nebular emission leads to systematic errors in age and mass estimates.

Careful modeling of nebular contributions is crucial for interpreting early galaxy observations.

Abstract

A substantial fraction of the light emitted from young or star-forming galaxies at ultraviolet to near-infrared wavelengths comes from the ionized interstellar medium in the form of emission lines and a nebular continuum. At high redshifts, star formation rates are on average higher and stellar populations younger than in the local Universe. Both of these effects act to boost the impact of nebular emission on the overall spectrum of galaxies. Even so, the broadband fluxes and colours of high-redshift galaxies are routinely analyzed under the assumption that the light observed originates directly from stars. Here, we assess the impact of nebular emission on broadband fluxes in Johnson/Cousins BVRIJHK, Sloan Digital Sky Survey griz and Spitzer IRAC/MIPS filters as a function of observed redshift (up to z=15) for galaxies with different star formation histories. We find that nebular emission may account for a non-negligible fraction of the light received from high-redshift galaxies. The ages and masses inferred for such objects through the use of spectral evolutionary models that omit the nebular contribution are therefore likely to contain systematic errors. We argue that a careful treatment of the nebular component will be essential for the interpretation of the rest-frame ultraviolet-to-infrared properties of the first galaxies formed, like the ones expected to be detected with the James Webb Space Telescope.