The LICK AGN MONITORING PROJECT: BROAD-LINE REGION RADII AND BLACK HOLE MASSES FROM REVERBERATION MAPPING OF Hβ

Abstract

We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3-m Shane telescope with the aim of measuring the masses of the black holes in 12 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ∼ 10 6 -10 7 M ⊙ and also the well-studied nearby active galactic nucleus (AGN) NGC 5548. Nine of the objects in the sample (including NGC 5548) showed optical variability of sufficient strength during the monitoring campaign to allow for a time lag to be measured between the continuum fluctuations and the response to these fluctuations in the broad Hβ emission. We present here the light curves for all the objects in this sample and the subsequent Hβ time lags for the nine objects where these measurements were possible. The Hβ lag time is directly related to the size of the broad-line region in AGNs, and by combining the Hβ lag time with the measured width of the Hβ emission line in the variable part of the spectrum, we determine the virial mass of the central supermassive black hole in these nine AGNs. The absolute calibration of the black hole masses is based on the normalization derived by Onken et al., which brings the masses determined by reverberation mapping into agreement with the local M BH − σ ⋆ relationship for quiescent galaxies. We also examine the time lag response as a function of velocity across the Hβ line profile for six of the AGNs. The analysis of four leads to rather ambiguous results with relatively flat time lags as a function of velocity. However, SBS 1116+583A exhibits a symmetric time lag response around the line center reminiscent of simple models for circularly orbiting broad-line region (BLR) clouds, and Arp 151 shows an asymmetric profile that is most easily explained by a simple gravitational infall model. Further investigation will be necessary to fully understand the constraints placed on physical models of the BLR by the velocityresolved response in these objects.

AGN Reverberation Mapping

“…Added to this uncertainty is the fact that AGN variations are stochastic and not guaranteed to occur during the course of a monitoring campaign for any particular AGN of interest (cf. the case of Mrk 290 which was monitored in 2007 and showed strong variations as reported by Denney et al 2010, but according to Bentz et al 2009b showed little to no variation when it was monitored again in 2008). The typical warning for the stock market also applies here: past performance is no guarantee of future behavior.…”

“…While the agreement is reassuring for these two objects, a sample of two is hardly definitive. Two more AGNs with reverberation masses -NGC 6814 (Bentz et al, 2009b) and NGC 5273 (Bentz et al, 2014) -are in various stages of the dynamical modeling process, and a handful of other AGNs are being targeted for reverberationmapping with the hope of dynamical modeling to follow. Fig.…”

“…Notable early attempts include Wanders et al (1995), Done & Krolik (1996), and Ulrich & Horne (1996), but recovered maps of velocity-resolved results, reminiscent of those shown in Figure 5, were ambiguous at best. In the last few years, however, reverberation programs have enjoyed much more success given the careful experimental setup and the resultant high quality of the data (Bentz et al 2009b(Bentz et al , 2010aDenney et al 2010;Grier et al 2012;De Rosa et al 2015).…”

“…The overall shape is different for each of the three models: a symmetric structure around zero velocity for circular Keplerian orbits, longer lags in the blueshifted emission for infall, and longer lags in the redshifted emission for outflow. From Bentz et al (2009b). Figure 6 shows an example of the deconvolved response of the broad optical recombination lines in the spectrum of the Seyfert galaxy Arp 151 (Bentz et al, 2010a).…”

Evolution of the MBH–σ and MBH–Lbulge Relations

“…Although active galaxies with measured reverberation black hole masses seem to follow the same M BH -σ relation as non-AGN galaxies (Gebhardt et al 2000b;Ferrarese et al 2001), it has not been clearly shown whether the M BH -σ relation of active galaxies has the same slope and scatter, due to the limited sample size and the black hole mass range of the local AGNs with reliable reverberation mass and stellar velocity dispersion measurements. Recently, Bentz et al (2009b) reported new reverberation measurements for a sample of eight local Seyfert galaxies, and stellar velocity dispersions of these galaxies were measured by Woo et al (2009). The MBH -σ relation of active galaxies in the present-day universe from Woo et al (2009).…”