Evidence for Two Distinct Broad-Line Regions from Reverberation Mapping of PG 0026+129

TL;DR

This study uses reverberation mapping to identify two distinct broad-line regions in quasar PG 0026+129, revealing different dynamics and origins for the emission line components, and estimating the black hole mass.

Contribution

It provides evidence for two separate broad-line regions with different physical properties and origins in a quasar, based on detailed spectroscopic monitoring and analysis.

Findings

Identification of two broad-line components with different widths and lags.

Hβ_IC shows a long lag and possible infall motion.

Hβ_VBC exhibits a near-zero lag and disk-like profile.

Abstract

We report on the results of a new spectroscopic monitoring campaign of the quasar PG 0026+129 at the Calar Alto Observatory 2.2m telescope from July 2017 to February 2020. Significant variations in the fluxes of the continuum and broad-emission lines, including H$\beta$ and He II, were observed in the first and third years, and clear time lags between them are measured. The broad H$\beta$ line profile consists of two Gaussian components: an intermediate-width H$\beta_{\rm IC}$ with a full width at half-maximum (FWHM) of 1964$\pm$18 $\rm km~s^{-1}$ and another very broad H$\beta_{\rm VBC}$ with a FWHM of 7570$\pm$83 $\rm km~s^{-1}$. H$\beta_{\rm IC}$ has long time lags of $\sim$40--60 days in the rest frame, while H$\beta_{\rm VBC}$ shows nearly zero time delay with respect to the optical continuum at 5100 \AA. The velocity-resolved delays show consistent results: lags of $\sim$30--50 days at the core of the broad H$\beta$ line and roughly zero lags at the wings. H$\beta_{\rm IC}$ has a redshift of $\sim$400 $\rm km~s^{-1}$ which seems to be stable for nearly 30 years by comparing with archived spectra, and may originate from an infall. The root mean square (rms) spectrum of H$\beta_{\rm VBC}$ shows a double-peaked profile with brighter blue peak and extended red wing in the first year, which matches the signature of a thin disk. Both the double-peaked profile and the near-zero lag suggest that H$\beta_{\rm VBC}$ comes from a region associated with the part of the accretion disc that emits the optical continuum. Adopting the FWHM (in the rms spectrum) and the time lag measured for the total H$\beta$ line, and a virial factor of 1.5, we obtain a virial mass of $2.89_{-0.69}^{+0.60} \times10^7 M_{\odot}$ for the central black hole in this quasar.