Calibrating Emission Lines as Quasar Bolometers

TL;DR

This paper develops and validates new formulae to estimate the bolometric luminosity of quasars using emission line strengths, demonstrating improved accuracy over previous methods and enabling insights into jet power.

Contribution

It introduces new, more accurate estimators for quasar bolometric luminosity based on emission lines, validated with SDSS data, and explores their application to radio jet power estimation.

Findings

Broad lines, especially Hβ, are the most reliable estimators of $L_{bol}$.

New formulae outperform archival estimators in accuracy.

Simultaneous use of multiple lines provides additional insights into jet power.

Abstract

Historically, emission lines have been considered a valuable tool for estimating the bolometric thermal luminosity of the accretion flow in AGN, $L_{bol}$. We study the reliability of this method by comparing line strengths to the optical/UV continuum luminosity of SDSS DR7 radio quiet quasars with $0.4<z<0.8$. We find formulae for $L_{bol}$ as a function of single line strengths for the broad components of H$\beta$ and Mg II, as well as the narrow lines of [O III] and [O II]. We determine the standard errors of the formulae that are fitted to the data. Our new estimators are shown to be more accurate than archival line strength estimations in the literature. It is demonstrated that the broad lines are superior estimators of the continuum luminosity (and $L_{bol}$) with $H\beta$ being the most reliable. The fidelity of the each of the estimators is determined in the context of the SDSS DR7 radio loud quasars as an illustrative application of our results. In general, individual researchers can use our results as a tool to help decide if a particular line strength provides an adequate estimate of $L_{bol}$ for their purposes. Finally, it is shown that considering all four line strength, simultaneously, can yield information on both $L_{bol}$ and the radio jet power.