width, a third parameter is required to obtain accurate masses and that parameter seems to be Eddington ratio. We present simplified empirical formulae for estimating black hole masses from the $\lambda4861$ and $\lambda1549$ emission lines.'
author:
- Elena Dalla Bontà
- 'Bradley M. Peterson'
- 'Misty C. Bentz'
- 'W. N. Brandt'
- 'S. Ciroi'
- Gisella De Rosa
- Gloria Fonseca Alvarez
- 'Catherine J. Grier'
- 'P. B. Hall'
- 'Juan V. Hernández Santisteban'
- 'Luis C. Ho'
- 'Y. Homayouni'
- Keith Horne
- 'C. S. Kochanek'
- 'Jennifer I-Hsiu Li'
- 'L. Morelli'
- 'A. Pizzella'
- 'R. W. Pogge'
- 'D. P. Schneider'
- Yue Shen
- 'J. R. Trump'
- Marianne Vestergaard
title: 'THE SLOAN DIGITAL SKY SURVEY REVERBERATION MAPPING PROJECT: ESTIMATING MASSES OF BLACK HOLES IN QUASARS WITH SINGLE-EPOCH SPECTROSCOPY'
---

Introduction {#section:intro}
============

Reverberation-Based Black Hole Masses
-------------------------------------

The presence of emission lines with Doppler widths of thousands of kilometers per second is one of the defining characteristics of active galactic nuclei [@Burbidge67; @Weedman76]. It was long suspected that the large line widths were due to motions in a deep gravitational potential and this implied very large central masses [e.g., @Woltjer59], as 