2025A&A...693A.153D

Context. Quasar outflows are key players in the feedback processes that influence the evolution of galaxies and the intergalactic medium. The chemical abundance of these outflows provides crucial insights into their origin and impact.
Aims. We determine the absolute abundances of nitrogen and sulfur and the physical conditions of the outflow seen in quasar 3C298.
Methods. We analyzed archival spectral data from the Hubble Space Telescope for 3C298. We measured the ionic column densities from the absorption troughs and compared the results to photoionization predictions made with the Cloudy code for three different spectral energy distributions (SEDs), including MF87, UV-soft, and HE0238 SEDs. We also calculated the ionic column densities of the excited and ground states of N III to estimate the electron number density and location of the outflow using the Chianti atomic database.
Results. The MF87, UV-soft, and HE0238 SEDs yield nitrogen and sulfur abundances at supersolar, solar, and subsolar values, respectively, with a spread of 0.4-3 times solar. Additionally, we determined an electron number density of log(n_e)≥3.3 cm^–3, and the outflow might extend up to a maximum distance of 2.8 kpc.
Conclusions. Our results indicate a solar metallicity within an uncertainty range of 60% that is driven by variations in the chosen SED and photoionization models. This study underscores the importance of the SED impact on determining chemical abundances in quasar outflows. These findings highlight the necessity of considering a wider range of possible abundances that span from subsolar to supersolar values.