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I am currently working on tests of the warped disc idea, especially with a combined WISE-UKIDSS-SDSS sample. Potentially this holds clues to the Physics of AGN we can't get any other way.My current PDRA Isaac Roseboom just led a paper deriving the distribution of covering factors for high luminosity quasars, showing pretty good agreement with the warped disc model. My 1987 Nature paper on NGC 4051 had the first light curve of high enough quality to take this seriously, but showed a featureless power law power spectrum.A research team that includes Penn State astronomers has discovered a surprising new class of quasars in distant galaxies that even the most current theories had not predicted.
In a 1993 paper Iossif Papadakis and I showed that the amplitude of the power spectrum correlates with luminosity, probably due to an underlying correlation with black hole mass, a suspicion strengthened by finding unnusually fast variability in the least luminous known AGN, NGC4395.
This was work led by Paulina Lira in 1999, Kazushi Iwasawa in 2000, and Jess Skelton in 2005.
(I will soon be writing up other results from Jess' thesis, showing that the correlation really is with black hole mass.) With Omar Almaini and James Manners, we showed in a 2002 paper that this variability-luminosity relation changes at high redshift, probably because earlier than z=2, black holes were still growing, and typically accreting at higher rates.
An exciting new area is that of Tidal Disruption Events, where a star is ripped apart as it passes close to a quiescent black hole, leading to a months-long eruption of quasar-like activity.
"If the gas is falling into the black hole, then we don't understand why it's so rare to see infalling gas. If gas can be seen falling into them, why not in other quasars?
" Hall noted there is one other possible explanation for these objects.
The most exciting initial result is in this Nature paper. I have also worked on and off on the spectral energy distributions of AGN, and testing the hypothesis of accretion discs. In a 2003 paper with Evlabia Rokaki, we showed that in AGN showing superluminal motions, where you can estimate the viewing angle, there are surface brightness and velocity effects with angle just as you would expect for a flat disc.
In a 2005 paper I showed that the colour differences between objects of different luminosity show just the trend one expects for a thermal emitter.
This discovery is detailed in a peer-reviewed paper in a recent issue of the journal Monthly Notices of the Royal Astronomical Society, published by Oxford University Press.
and Distinguished Professor of Astronomy and Astrophysics Donald Schneider, who also is the survey coordinator and scientific publication coordinator for SDSS-III.