The Origin of Wavelength-Dependent Continuum Delays in AGNs - a New Model

A model of wavelength-dependent lags in optical continuum variability of AGNs is proposed which avoids the problems of the popular ``lamp-post'' model. Rather than being due to reprocessing of high-energy radiation from a hypothetical source above the accretion disk, the wavelength-dependent delays observed from the B to I bands are instead due to contamination of an intrinsically coherently variable continuum with the Wien tail of the thermal emission from the hot dust in the surrounding torus. The new model correctly gives the size, wavelength dependence, and luminosity dependence of the lags, and quantitatively predicts observed color hysteresis. The model also explains how the measured delays vary with epoch of observation. There must also be contamination by scattered light and this can be detected by a lag in the polarized flux.Comment: To appear in "The Central Engine of Active Galactic Nuclei", ed. L. C. Ho and J.-M. Wang (San Francisco: Astronomical Society of the Pacific). 4 pages. 2 diagram

Accurate AGN black hole masses and the scatter in the M_{bh} - L_{bulge} relationship

A new empirical formulae is given for estimating the masses of black holes in AGNs from the H beta velocity dispersion and the continuum luminosity at 5100 Angstroms. It is calibrated to reverberation-mapping and stellar-dynamical estimates of black hole masses. The resulting mass estimates are as accurate as reverberation-mapping and stellar-dynamical estimates. The new mass estimates show that there is very little scatter in the M_{bh} - L_{bulge} relationship for high-luminosity galaxies, and that the scatter increases substantially in lower-mass galaxies.Comment: In press in "Co-Evolution of Central Black Holes and Galaxies", IAU Symposium Proceedings No. 267, eds. B. M. Peterson, R. S. Somerville, & T. Storchi-Bergmann. Cambridge University Press, 2010. 1 figur

The origin of the relationship between black hole mass and host galaxy bulge luminosity

There is a strong decrease in scatter in the black hole mass versus bulge luminosity relationship with increasing luminosity and very little scatter for the most luminous galaxies. It is shown that this is a natural consequence of the substantial initial dispersion in the ratio of black hole mass to total stellar mass and of subsequent galaxy growth through hierarchical mergers. "Fine-tuning" through feedback between black hole growth and bulge growth is neither necessary nor desirable.Comment: In press in "The First Stars and Galaxies: Challenges for the Next Decade", America Institute of Physics Conf. Proc., eds. D. Whalen, V. Bromm, & N. Yoshida. 1 figure

Line Shifts, Broad-Line Region Inflow, and the Feeding of AGNs

Velocity-resolved reverberation mapping suggests that the broad-line regions (BLRs) of AGNs can have significant net inflow. We use the STOKES radiative transfer code to show that electron and Rayleigh scattering off the BLR and torus naturally explains the blueshifted profiles of high-ionization lines and the ionization dependence of the blueshifts. This result is insensitive to the geometry of the scattering region. If correct, this model resolves the long-standing conflict between the absence of outflow implied by velocity-resolved reverberation mapping and the need for outflow if the blueshifting is the result of obscuration. The accretion rate implied by the inflow is sufficient to power the AGN. We suggest that the BLR is part of the outer accretion disk and that similar MHD processes are operating. In the scattering model the blueshifting is proportional to the accretion rate so high-accretion-rate AGNs will show greater high-ionization line blueshifts as is observed. Scattering can lead to systematically too high black hole mass estimates from the C IV line. We note many similarities between narrow-line region (NLR) and BLR blueshiftings, and suggest that NLR blueshiftings have a similar explanation. Our model explains the higher blueshifts of broad absorption line QSOs if they are more highly inclined. Rayleigh scattering from the BLR and torus could be more important in the UV than electron scattering for predominantly neutral material around AGNs. The importance of Rayleigh scattering versus electron scattering can be assessed by comparing line profiles at different wavelengths arising from the same emission-line region.Comment: 10 pages, 7 figures, Astrophysical Journal in press. The only changes from the previous version are to include some additional discussion of the plausibility of supersonic inflow velocities (see section 5.2) and some additional reference