Star-forming emission influence on metallicity determination of Quasars at high redshift

Abstract

Recent observations of quasars have provided to observe the host galaxy of these objects where one can see, for some cases, regions with a high rate of star formation (SFR), of the order of 200 M˜/year up to 3000 M˜/year for objects with high redshift (z ~ 6). Until the moment, metallicity (Z) determinations in this class of objects, mostly based on photoionization models, have not considered the contribution of the emission of star formation regions (SFs) in the observed flux of quasars, which can generate uncertain Z values. Motivated by these factors, this project has as main objective to study the influence of the emission of SFs in the determination of the metallicity of quasars. In view of this, we will use photoionization models constructed with Cloudy code, synthetic star spectra obtained with the STARBURST99 code and spectroscopic observational data in the ultraviolet region (UV; 1000 d »(Å) d 2000) compiled from the literature. Initially, we will build galaxy simulations containing SFs and a quasar (composite objects). We will consider a wide range of nebular and stellar parameters. Observational data comprise UV emission line flux of six quasars with redshift 1.5 d z d 3. Intensities of emission line ratios of the sample will be compared with those predicted by the composite photoionization models, which will provide us estimating the contribution of the emission of SFs to the observed flux of each object. Thus, we can estimate the uncertainty in the determination of the gas phase metallicity obtained from pure AGN photoionization models. Finally, as a secondary objective, we will build a photoionization grid in order to obtain transition regions between SFs and AGNs in diagnostic diagrams containing line ratios observed in the UV. (AU)