Identifying AGNs from X-ray detections

Abstract

Active galactic nuclei (AGNs) are challenging to identify, as any one indicator of black holeaccretion has its own limitations. Obtaining a comprehensive census of AGNs is essentialto assess their role in the host galaxy properties and the evolutionary processes they undergothroughout cosmic time. In general, a more complete census of AGNs can only be achievedwith a multiwavelength analysis. AGNs are shown to be dependent on gas-phase metallicity (Z) and AGNs with low metallicity (Z d 0.2Z™) tend to fall below the AGNs and starforming galaxies (SFGs) separation lines in the BPT diagnostic diagrams. This postdoctoralproject aims to explore the different analytical techniques used to classify AGN populations using X-ray selection criteria together with cross-correlation from optical spectroscopy database,e.g. data from the Swift-BAT AGN Spectroscopic Survey (BASS) or Sloan Sky Digital Survey(SDSS), as well as verifying their positions in the BPT diagnostic diagrams. Optical surveys estimation of the population of AGN in the local universe (at redshift, z < 1) are usually appliedto low-luminosity AGNs with lower metallicity which makes it difficult to disentangle AGNsfrom SFGs. Therefore, the uniqueness of this project is to classify AGNs taking into accountthe effects of electron density, galaxy stellar mass, low and high metallicity, nitrogen-to-oxygen(N/O) abundance ratio and the equivalent width of H± (WH±), which will help to produce statistical constraints on the evolution of the excitation and ionization properties of AGNs. Moreover, this project will contribute to current and ongoing efforts toward complete statistics of theAGN population and the implications of the diagnostic classifications for strong-line metallicity calibrations, as well as providing constraints for galaxy evolutionary models.