Optical Emission-Line Properties of eROSITA-selected SDSS-V Galaxies

TL;DR

This study analyzes optical emission line properties of X-ray selected SDSS galaxies, revealing correlations between emission lines, X-ray luminosity, and black hole mass, emphasizing the importance of emission line decomposition for AGN classification.

Contribution

It provides a detailed analysis of emission line properties in X-ray selected galaxies, demonstrating the significance of line decomposition in understanding AGN activity and its relation to X-ray emission.

Findings

Most galaxies shift to the AGN region on the BPT diagram after line decomposition.

Confirmed correlation between X-ray luminosity and emission line luminosities.

Established relationships between SMBH mass, X-ray luminosity, and stellar velocity dispersion.

Abstract

We present and discuss optical emission line properties obtained from the analysis of Sloan Digital Sky Survey (SDSS) spectra for an X-ray selected sample of 3684 galaxies (0.002 < z < 0.55), drawn from the eRASS1 catalog. We modeled SDSS-V DR19 spectra using the NBursts full spectrum fitting technique with E-MILES simple stellar populations (SSP) models and emission line templates to decompose broad and narrow emission line components for correlation with X-ray properties. We place the galaxies on the Baldwin-Phillips-Terlevich (BPT) diagram to diagnose their dominant excitation mechanism. We show that the consistent use of the narrow component fluxes shifts most galaxies systematically and significantly upward to the active galactic nuclei (AGN) region on the BPT diagram. On this basis, we confirm the dependence between a galaxys position on the BPT diagram and its (0.2-2.3 keV) X-ray/H$\alpha$ flux ratio. We also verified the correlation between X-ray luminosity and emission line luminosities of the narrow [O\iii]$\lambda 5007$ and broad H$\alpha$ component; as well as the relations between the Supermassive Black Hole (SMBH) mass, the X-ray luminosity, and the velocity dispersion of the stellar component ($\sigma_{*}$) on the base on the unique sample of optical spectroscopic follow-up of X-ray sources detected by eROSITA. These results highlight the importance of emission line decomposition in AGN classification and refine the connection between X-ray emission and optical emission line properties in galaxies.