Reverberation Mapping of the Broad-line Region in NGC 5548: Evidence for Radiation Pressure?
Abstract
NGC 5548 is the best-observed reverberation-mapped active galactic nucleus with long-term, intensive monitoring. Here we report results from a new observational campaign between 2015 January and July. We measure the centroid time lag of the broad Hβ emission line with respect to the 5100 Å continuum and obtain {τ }{{cent}}={7.20}-0.35+1.33 days in the rest frame. This yields a black hole mass of {M}\bullet ={8.71}-2.61+3.21× {10}7{M}⊙ using a broad Hβ line dispersion of 3124 ± 302 km s-1 and a virial factor of {f}{{{BLR}}}=6.3+/- 1.5 for the broad-line region (BLR), consistent with the mass measurements from previous Hβ campaigns. The high-quality data allow us to construct a velocity-binned delay map for the broad Hβ line, which shows a symmetric response pattern around the line center, a plausible kinematic signature of virialized motion of the BLR. Combining all the available measurements of Hβ time lags and the associated mean 5100 Å luminosities over 18 campaigns between 1989 and 2015, we find that the Hβ BLR size varies with the mean optical luminosity, but, interestingly, with a possible delay of {2.35}-1.25+3.47 years. This delay coincides with the typical BLR dynamical timescale of NGC 5548, indicating that the BLR undergoes dynamical changes, possibly driven by radiation pressure.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2016
- DOI:
- 10.3847/0004-637X/827/2/118
- arXiv:
- arXiv:1607.08060
- Bibcode:
- 2016ApJ...827..118L
- Keywords:
-
- galaxies: active;
- galaxies: individual: NGC 5548;
- galaxies: nuclei;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 24 pages, 10 figures, 5 tables