Metallicity evolution in quasars

TL;DR

This study investigates how metallicity indicators in quasar spectra evolve over cosmic time and relate to black hole properties, using SDSS data and PCA to analyze correlations and identify peculiar sources.

Contribution

It introduces a detailed analysis of metallicity evolution in quasars with a novel application of PCA to interpret spectroscopic data across redshifts.

Findings

Identification of primary drivers of metallicity correlations.

Validation of metallicity indicators through PCA.

Isolation of peculiar quasar sources.

Abstract

Broad-band spectra of active galaxies contain a wide range of information that help reveal the nature and activity of the central continuum source and their immediate surroundings. Understanding the evolution of metals in the spectra of Active Galactic Nuclei (AGN) and linking them with the various fundamental black hole (BH) parameters, for example, BH mass, the bolometric luminosity of the source, its accreting power, can help address the connection between the growth of the BH across cosmic time. We investigate the role of selected metallicity indicators utilizing the rich spectroscopic database of emission lines covering a wide range in redshift in the recent spectroscopic data release of Sloan Digital Sky Survey (SDSS). We make careful filtering of the parent sample to prepare a pair of high-quality, redshift-dependent sub-samples and present the first results of the analysis here. To validate our findings from the simple correlations, we execute and evaluate the performance of a linear dimensionality reduction technique - principal component analysis (PCA), over our sub-samples and present the projection maps highlighting the primary drivers of the observed correlations. The projection maps also allow us to isolate peculiar sources of potential interest.