Using photoionization models to derive carbon and oxygen gas-phase abundances in the rest UV

We present a new method to derive oxygen and carbon abundances using the ultraviolet (UV) lines emitted by the gas phase ionized by massive stars. The method is based on the comparison of the nebular emission-line ratios with those predicted by a large grid of photoionization models. Given the large dispersion in the O/H–C/O plane, our method first fixes C/O using ratios of appropriate emission lines and, in a second step, calculates O/H and the ionization parameter from carbon lines in the UV. We find abundances totally consistent with those provided by the direct method when we apply this method to a sample of objects with an empirical determination of the electron temperature using optical emission lines. The proposed methodology appears as a powerful tool for systematic studies of nebular abundances in star-forming galaxies at high redshift.
EPM acknowledges support from the Spanish MICINN through grants AYA2010-21887-C04-01 and AYA2013-47742-C4-1-P and the Junta de Andalucía for grant EXC/2011 FQM-7058. RA acknowledges the support from the ERC Advanced Grant 695671 ‘QUENCH’ and the FP7 SPACE project ‘ASTRODEEP’ (Ref. No.: 312725), supported by the European Commission.