NGC 5548 in a Low-Luminosity State: Implications for the Broad-Line Region

We describe results from a new ground-based monitoring campaign on NGC 5548, the best-studied reverberation-mapped AGN. We find that it was in the lowest luminosity state yet recorded during a monitoring program, namely L_5100 = 4.7 × 10^42 ergs s^-1. We determine a rest-frame time lag between flux variations in the continuum and the Hβ line of 6.3^+2.6 _-2.3 days. Combining our measurements with those of previous campaigns, we determine a weighted black hole mass of M_BH = 6.54^+.26_-.25 × 10^7 Msun based on all broad emission lines with suitable variability data. We confirm the previously discovered virial relationship between the time lag of emission lines relative to the continuum and the width of the emission lines in NGC 5548, which is the expected signature of a gravity-dominated broad-line region. Using this lowest luminosity state, we extend the range of the relationship between the luminosity and the time lag in NGC 5548 and measure a slope that is consistent with α = 0.5, the naive expectation for the broad-line region for an assumed form of r α L^α. This value is also consistent with the slope recently determined by Bentz et al. for the population of reverberation-mapped AGNs as a whole.

Keywords

galaxies: active, galaxies: nuclei, galaxies: Seyfert

Citation

Misty C. Bentz et al, "NGC 5548 in a Low-Luminosity State: Implications for the Broad-Line Region," The Astrophysical Journal 662, no. 1 (2007), doi:10.1086/516724

URI

http://hdl.handle.net/1811/48184

Collections

Ohio State University Research and Scholarship

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