Supermassive Black Hole Mass Estimates Using Sloan Digital Sky Survey Quasar Spectra at 0.7 < z < 2

TL;DR

This paper estimates supermassive black hole masses for over 27,000 quasars using MgII emission lines from SDSS spectra, employing a new method that improves accuracy especially for low-quality data.

Contribution

It introduces a novel mass estimation technique based on line dispersion and spectral reconstruction, enhancing reliability and reducing scatter in black hole mass measurements.

Findings

Reconstructed spectra enable bias-free mass estimates for low S/N quasars.

The method reduces intrinsic scatter in mass estimates to below 0.15 dex.

Validation shows the approach is consistent with reverberation mapping results.

Abstract

We present MgII-based black hole mass estimates for 27,602 quasars with rest-frame UV spectra available in the Sloan Digital Sky Survey Data Release Three. This estimation is possible due to the existence of an empirical correlation between the radius of the broad line region and the continuum luminosity at 3000 Angstroms. We regenerate this correlation by applying our measurement method to UV spectra of low-redshift quasars in the HST/IUE databases which have corresponding reverberation mapping estimates of the Hbeta broad line region's radius. Our mass estimation method uses the line dispersion rather than the full width at half maximum of the low-ionization MgII emission line. We measure MgII line dispersions for quasars whose spectra have been reconstructed using the most significant eigenspectra produced through Principal Component Analysis. We have tested the reliability of using reconstructed spectra in black hole mass estimation using a Monte Carlo simulation and by comparing the results from original and reconstructed Data Release Three spectra. We show that using reconstructed spectra not only makes bias-free mass estimation possible for quasars with low spectroscopic signal-to-noise ratio, but also reduces the intrinsic scatter of the distribution of the black hole masses to lower than 0.15 dex.