Comparing Hbeta Line Profiles in the 4D Eigenvector 1 Context

TL;DR

This paper introduces the 4D Eigenvector 1 space as a unifying framework for quasar spectra, revealing a potential dichotomy in H_beta line profiles that impacts black hole mass estimates and source structure understanding.

Contribution

It presents the 4DE1 space as a new classification scheme for quasars, highlighting a fundamental dichotomy in H_beta line profiles between two populations.

Findings

Quasars with FWHM H_beta < 4000 km/s (Pop. A) show Lorentzian profiles.

Quasars with FWHM H_beta > 4000 km/s (Pop. B) show double Gaussian profiles.

The dichotomy affects black hole mass estimation and source kinematics.

Abstract

We describe a 4D Eigenvector 1 (4DE1) space that serves as a surrogate H-R diagram for quasars. It provides a context for describing and unifying differences between all broad line AGN. Quasar spectra can be averaged in a non-random way using 4DE1 just as stellar spectra can be averaged non-randomly within the OBAFGKM classification sequence. We find that quasars with FWHM H_beta less than (Population A) and greater than (Population B) 4000 km/s show many significant differences that may point to an actual dichotomy. Broad line profile measures and fits reenforce the idea of a dichotomy because they are fundamentally different: Pop.A - Lorentzian-like and Pop.B - double Gaussian. The differences have implications both for BH mass estimation and for inferences about source structure and kinematics.