Published in Bulletin of the Astronomical Society of India, Vol. 41, No. 1, p. 61-115, 2013.
http://arxiv.org/abs/1302.2643

For a PDF version of the article, click here.

Abstract: I review the current status of quasar black hole (BH) mass estimations. Spectroscopic methods have been developed to estimate BH mass in broad line quasars to an accuracy of ~ 0.5 dex. Despite their popularity, significant issues and confusion remain regarding these mass estimators. I provide an in-depth discussion on the merits and caveats of the single-epoch (SE) virial BH mass estimators, and a detailed derivation of the statistical biases of these SE mass estimates resulting from their errors. I show that error-induced sample biases on the order of a factor of several are likely present in the SE mass estimates for flux-limited, statistical quasar samples, and the distribution of SE masses in finite luminosity bins can be narrower than the nominal uncertainty of these mass estimates. I then discuss the latest applications of SE virial masses in quasar studies, including the early growth of supermassive black holes, quasar demography in the mass-luminosity plane, and the evolution of the BH-host scaling relations, with specific emphases on selection effects and sample biases in the SE masses. I conclude that there is a pressing need to understand and deal with the errors in these BH mass estimates, and to improve these BH weighing methods with substantially more and better reverberation mapping data.

Keywords : black hole physics — galaxies: active — quasars:general — surveys

Table of Contents

• INTRODUCTION
• METHODS TO MEASURE QUASAR BH MASSES
• Virial BH Masses: From Reverberation Mapping to Single-Epoch Methods
• Other Methods to Estimate Quasar BH Masses
• CAVEATS, UNCERTAINTIES, AND BIASES OF VIRIAL BH MASSES
• Physical Concerns
• Practical Concerns
• Consequences of the Uncertainties in SE Mass Estimates
• APPLICATIONS TO STATISTICAL QUASAR SAMPLES
• Early Growth of SMBHs
• Quasar Demographics in the Mass-Luminosity Plane
• Evolution of BH-Bulge Scaling Relations
• SUMMARY AND FUTURE PERSPECTIVES
• REFERENCES

^* In this review I use the terms "quasar" and "Active Galactic Nucleus (AGN)" interchangeably to refer to all active supermassive black holes, although traditionally quasars are loosely defined as the luminous (L_bol 10¹² L) subset of AGNs. By default I use quasars and AGNs to refer to unobscured (Type 1), broad-line objects unless otherwise specified.