Off-Axis Energy Variability of AGNs: a New Paradigm for Broad-Line- and Continuum-Emitting Regions

The general picture of how thermal AGNs work has become clearer in recent years but major observational puzzles threaten to undermine this picture. These puzzles include AGNs with extremely asymmetric emission line profiles, inconsistent multi-wavelength variability, rapid apparent changes in the sizes of emitting regions and in the direction of gas flow, a curious insensitivity of gas in some narrow velocity ranges to changes in the ionizing continuum, and differing dependencies of polarization on gas velocity. It is proposed that all these puzzles can readily be explained by off-axis variability, and that there is no need to invoke exotic explanations such as binary supermassive black holes or recoiling black holes.Comment: Invited talk given at 8th SCSLS. Accepted for publication in Baltic Astronomy, Vol. 20. 8 pages, 8 figure

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 case for cases B and C: intrinsic hydrogen line ratios of the broad-line region of active galactic nuclei, reddenings, and accretion disc sizes

Low-redshift active galactic nuclei (AGNs) with extremely blue optical spectral indices are shown to have a mean, velocity-averaged, broad-line H$\alpha$/H$\beta$ ratio of $\thickapprox 2.72 \pm 0.04$, consistent with a Baker-Menzel Case B value. Comparison of a wide range of properties of the very bluest AGNs with those of a luminosity-matched subset of the Dong et al. blue AGN sample indicates that the only difference is the internal reddening. Ultraviolet fluxes are brighter for the bluest AGNs by an amount consistent with the flat AGN reddening curve of Gaskell et al.(2004). The lack of a significant difference in the GALEX (FUV--NUV) colour index strongly rules out a steep SMC-like reddening curve and also argues against an intrinsically harder spectrum for the bluest AGNs. For very blue AGNs the Ly$\alpha$/H$\beta$ ratio is also consistent with being the Case B value. The Case B ratios provide strong support for the self-shielded broad-line model of Gaskell, Klimek & Nazarova. It is proposed that the greatly enhanced Ly$\alpha$/H$\beta$ ratio at very high velocities is a consequence of continuum fluorescence in the Lyman lines (Case C). Reddenings of AGNs mean that the far-UV luminosity is often underestimated by up to an order of magnitude. This is a major factor causing the discrepancies between measured accretion disc sizes and the predictions of simple accretion disc theory. Dust covering fractions for most AGNs are lower than has been estimated. The total mass in lower mass supermassive black holes must be greater than hitherto estimated.Comment: 15 pages, 6 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Societ

Close supermassive binary black holes

It has been proposed that when the peaks of the broad emission lines in active galactic nuclei (AGNs) are significantly blueshifted or redshifted from the systemic velocity of the host galaxy, this could be a consequence of orbital motion of a supermassive blackhole binary (SMB) (Gaskell 1983). The AGN J1536+0441 (=SDSS J153636.22+044127.0) has recently been proposed as an example of this phenomenon (Boroson & Lauer 2009). It is proposed here instead that 1536+044 is an example of line emission from a disc. If this is correct, the lack of clear optical spectral evidence for close SMBs is significant and argues either that the merging of close SMBs is much faster than has generally been hitherto thought, or if the approach is slow, that when the separation of the binary is comparable to the size of the torus and broad-line region, the feeding of the black holes is disrupted.Comment: Nature in press. 4 pages, 1 figure [Title, abstract, text, and references shortened to conform to journal requirements

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

Marine pollution damage in Australia: implementing the Bunker Oil Convention 2001 and the Supplementary Fund Protocol 2003

The grounding of the bulk carrier Pasha Bulker on Nobbys beach, Newcastle in June 2007 has again highlighted the risk from shipping posed to Australia’s extensive and environmentally fragile coastline. Whilst a pollution incident was averted in this case, spills from shipping in other states (such as the Nakhodka spill off Japan in 1997, the Prestige spill off France in 1999, the Erika spill off Spain in 2003 and the Hebei Spirit spill of South Korea in 2007), have required the constant monitoring and updating of the international regulatory regimes designed to prevent such incidents occurring and to provide compensation when they nevertheless do occur. Two recent additions to this international regulatory system are the Protocol on the Establishment of a Supplementary Fund for Oil Pollution Damage 2003, (the “Supplementary Fund Protocol 2003”) and the International Convention on Civil Liability for Bunker Oil Pollution Damage 2001 (“the Bunker Oil Convention 2001”). In 2008, Australia gave effect to these instruments, enacting the Supplementary Fund Protocol via the Protection of the Sea Legislation Amendment Act 2008 (Cth), while the Bunker Oil Convention is given effect through the Protection of the Sea (Civil Liability for Bunker Oil Pollution Damage) Act 2008 (Cth), and the Protection of the Sea (Civil Liability For Bunker Oil Pollution Damage) (Consequential Amendments) Act 2008 (Cth). The purpose of this article is to analyse these international instruments, describe how they came about, and explain the Australian implementation of them. In particular, consideration is given to the question of limitation of liability, especially the relationship between bunker pollution claims and the Convention on Limitation of Liability for Maritime Claims (LLMC) 1976, as amended in 1996

A Look at What Is (and Isn't) Known About Quasar Broad Line Regions and How Narrow-Line Seyfert 1 Galaxies Fit In

The evidence is reviewed that the Broad Line Region (BLR) probably has two distinct components located at about the same distance from the central black hole. One component, BLR II, is optically-thick, low-ionization emission at least some of which arises from a disc and the other, BLR I, is probably optically-thin emission from a more spherically symmetric halo or atmosphere. The high Fe II/H-beta ratios seen in Narrow-Line Seyfert 1 galaxies (NLS1s) are not due to strong Fe II emission, as is commonly thought, but to unusually weak Balmer emission, probably caused by higher densities. NLS1s probably differ from non-NLS1s because of the higher density of gas near the black hole. This produces a higher accretion rate, a denser BLR, and a view of the central regions that is more face-on.Comment: Contributed talk presented at the Joint MPE,AIP,ESO workshop on NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho