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

The case for inflow of the broad-line region of active galactic nuclei

The high-ionization lines of the broad-line region (BLR) of thermal active galactic nuclei (AGNs) show blueshifts of a few hundred km/s to several thousand km/sec with respect to the low-ionization lines. This has long been thought to be due to the high-ionization lines of the BLR arising in a wind of which the far side of the outflow is blocked from our view by the accretion disc. Evidence for and against the disc-wind model is discussed. The biggest problem for the model is that velocity-resolved reverberation mapping repeatedly fails to show the expected kinematic signature of outflow of the BLR. The disc-wind model also cannot readily reproduce the red side of the line profiles of high-ionization lines. The rapidly falling density in an outflow makes it difficult to obtain high equivalent widths. We point out a number of major problems with associating the BLR with the outflows producing broad absorption lines. An explanation which avoids all these problems and satisfies the constraints of both the line profiles and velocity-resolved reverberation-mapping is a model in which the blueshifting is due to scattering off material spiraling inwards with an inflow velocity of half the velocity of the blueshifting. We discuss how recent reverberation mapping results are consistent with the scattering-plus-inflow model but do not support a disc-wind model. We propose that the anti-correlation of the apparent redshifting of H$\beta$ with the blueshifting of CIV is a consequence of contamination of the red wings of H$\beta$ by the broad wings of [O III].Comment: 15 pages, 15 figures. To appear in special issue of Astrophysics and Space Science, "Spectral Line Shapes in Astrophysics