Data-driven dissection of emission-line regions in Seyfert galaxies

TL;DR

This paper introduces a data-driven correlation method to identify emission-line regions in Seyfert galaxies, revealing links between emission lines, host galaxy morphology, and AGN properties, with potential to complement reverberation mapping.

Contribution

The study presents a novel correlation-based approach to dissect emission-line regions in AGN, tested on SDSS Seyfert galaxies, and explores its relation to reverberation mapping results.

Findings

Similar narrow-line regions in Seyfert-1 and Seyfert-2 galaxies.

Emission line presence depends on host galaxy morphology and radio-loudness.

Correlation coefficients relate to reverberation mapping time lags.

Abstract

Indirectly resolving the line-emitting gas regions in distant Active Galactic Nuclei (AGN) requires both high-resolution photometry and spectroscopy (i.e. through reverberation mapping). Emission in AGN originates on widely different scales; the broad-line region (BLR) has a typical radius less than a few parsec, the narrow-line region (NLR) extends out to hundreds of parsecs. But emission also appears on large scales from heated nebulae in the host galaxies (tenths of kpc). We propose a novel, data-driven method based on correlations between emission-line fluxes to identify which of the emission lines are produced in the same kind of emission-line regions. We test the method on Seyfert galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) and Galaxy Zoo project. We demonstrate the usefulness of the method on Seyfert-1s and Seyfert-2 objects, showing similar narrow-line regions (NLRs). Preliminary results from comparing Seyfert-2s in spiral and elliptical galaxy hosts suggest that the presence of particular emission lines in the NLR depends both on host morphology and eventual radio-loudness. Finally, we explore an apparent linear relation between the final correlation coefficient obtained from the method and time lags as measured in reverberation mapping for Zw229-015.