Speaker
Description
The chemical abundance of active galaxies, which host active galactic nuclei (AGN) at their centre, remains poorly studied, most often due to the difficulty of removing the effect of AGN in metallicity measurements. In particular, the chemical abundance of active galaxies in different environments, including clusters and groups of galaxies, is still unknown. In this work, we use a novel HCm code (HII-CHI-mistry) adapted to measure the chemical abundance of type-2 AGN. We measure the
oxygen abundance (12 + log(O/H)), the nitrogen abundance (log(N/O)), and the ionisation parameter (logU) for ~ 12000 type-2 AGN selected from the SDSS survey. We analyse the metallicity properties of type-2 AGNs in relation to other properties of AGN host galaxies, such as morphology, stellar mass and star formation rate (SFR), and in terms of the environment. In addition, for galaxies in groups and clusters, we study the metallicity properties in relation to the properties of the galaxy groups/clusters (e.g., the cluster-centric distance and the number of galaxies in the group/cluster). We do not observe a clear and strong mass-metallicity relation, although, we do observe that in groups and clusters, the 12 + log(O/H) abundance is higher in galaxies with higher stellar mass. We find that the 12 + log(O/H) abundance decreases with increasing SFR in all environments. We do not find a fundamental plane of type-2 AGN, suggesting more complex scenarios in the behaviour of stellar mass, SFR and metallicity when AGN are present, compared to pure star-forming galaxies. We find that type-2 AGN hosts, both early- and late-type, have on average higher 12 + log(O/H) abundances in groups and clusters compared to field galaxies, independent of redshift. Our results indicate that, although type-2 AGN in groups and clusters have on average higher metallicities for a given stellar mass, neither simple group or cluster membership nor cosmic-centric distance seems to drive this effect. Finally, with this work, we provide the largest catalogue of chemical abundances of type-2 AGN to date.
