The relation between broad lines and gamma--ray luminosities in Fermi blazars

TL;DR

This study investigates the correlation between broad line luminosities and gamma-ray luminosities in Fermi blazars, revealing a link to the division between BL Lacs and FSRQs based on Eddington ratios.

Contribution

It provides new evidence connecting broad line emission and gamma-ray output, clarifying the blazar classification scheme based on accretion properties.

Findings

Strong correlation between broad line and gamma-ray luminosities.

Blazar type depends on Eddington ratio of line luminosity.

Transition between BL Lacs and FSRQs appears smooth.

Abstract

We study the relation between the mass accretion rate, the jet power, and the black hole mass of blazars. To this aim, we make use of the Sloan Digital Sky Survey (SDSS) and the 11 months catalog of blazars detected at energies larger than 100 MeV by the Large Area Telescope (LAT) onboard the Fermi satellite. This allows to construct a relatively large sample of blazars with information about the luminosity (or upper limits) of their emission lines used as a proxy for the strength of the disc luminosity and on the luminosity of the high energy emission, used as a proxy for the jet power. We find a good correlation between the luminosity of the broad lines and the gamma-ray luminosity as detected by Fermi, both using absolute values of the luminosities and normalising them to the Eddington value. The data we have analyzed confirm that the division of blazars into BL Lacs and Flat Spectrum Radio Quasars (FSRQs) is controlled by the line luminosity in Eddington units. For small values of this ratio the object is a BL Lac, while it is a FSRQs for large values. The transition appears smooth, but a much larger number of objects is needed to confirm this point.