Comparing and calibrating black hole mass estimators for distant active galactic nuclei

TL;DR

This study compares various black hole mass estimation methods for distant active galactic nuclei using spectra from Keck and SDSS, revealing discrepancies and providing a set of self-consistent calibration recipes.

Contribution

It systematically evaluates the accuracy and consistency of different black hole mass estimators at z=0.36, offering a unified set of calibration recipes and quantifying their uncertainties.

Findings

Mass estimates differ up to 0.38 dex between recipes.

Self-consistent recipes reduce scatter to 0.1-0.3 dex.

Systematic differences could affect evolutionary studies.

Abstract

Black hole mass is a fundamental property of active galactic nuclei (AGNs). In the distant universe, black hole mass is commonly estimated using the MgII, Hbeta, or Halpha emission line widths and the optical/UV continuum or line luminosities, as proxies for the characteristic velocity and size of the broad-line region. Although they all have a common calibration in the local universe, a number of different recipes are currently used in the literature. It is important to verify the relative accuracy and consistency of the recipes, as systematic changes could mimic evolutionary trends when comparing various samples. At z=0.36, all three lines can be observed at optical wavelengths, providing a unique opportunity to compare different empirical recipes. We use spectra from the Keck Telescope and the Sloan Digital Sky Survey to compare black hole mass estimators for a sample of nineteen AGNs at this redshift. We compare popular recipes available from the literature, finding that mass estimates can differ up to 0.38+-0.05 dex in the mean (or 0.13+-0.05 dex, if the same virial coefficient is adopted). Finally, we provide a set of 30 internally self consistent recipes for determining black hole mass from a variety of observables. The intrinsic scatter between cross-calibrated recipes is in the range 0.1-0.3 dex. This should be considered as a lower limit to the uncertainty of the black hole mass estimators.