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Chapter 1
SCIENTIFIC HIGHLIGHTS
OUTFLOWS FROM AGNS ORIGINATE AS
DISK WINDS ORBITING A SUPER-MASSIVE
BLACK HOLE
Most galaxies undergo an active phase, during which a
central super-massive black hole generates vast radiant
luminosities through the gravitational accretion of gas.
Winds launched from a rotating accretion disk surrounding
the black hole are thought to play a critical role, allowing
the disk to shed angular momentum that would otherwise
inhibit accretion. Such winds are capable of depositing
large amounts of mechanical energy in the host galaxy and
its environs, profoundly affecting its formation and
evolution, and perhaps regulating the formation of largescale
cosmological structures in the early Universe.
However, observational verification that AGN outflows
originate as disk winds has proven elusive.
Using the ISIS spectrograph in its spectropolarimetric mode
on the WHT, a team of astronomers was able to obtain the
first observational evidence that indeed outflows from active
galactic nuclei originate as winds from rotating accretion
disks surrounding a super-massive black hole. The
evidence came from observations of the quasar PG
1700+518 and some of the results can be seen in Figure 1.
A GIANT OUTBURST TWO YEARS BEFORE
THE CORE-COLLAPSE OF A MASSIVE STAR
For the first time, astronomers witnessed a double stellar
explosion at exactly the same position on the sky,
suggesting the death of a massive star.
SN 2006jc was discovered in UGC 4904 on 2006 October 9.
The early spectrum was that of a hydrogen-poor event with
strong, narrow HeI emission lines superimposed on a broadline
spectrum of a type Ic supernova. In 2004, an optical
transient was reported which, when retrospectively
compared with the SN 2006jc discovery images, appeared to
be spatially coincident with the supernova. The 2004
transient was much fainter than SN 2006jc and it remained
visible for only a few days after discovery. Given the new
Figure 1. The polarisation data for the BAL quasar PG1700+518.
The data were obtained using ISIS spectrograph on the WHT, at a
spectral resolution of 3.4 Å. The polarisation data have been resampled
into bins with an error of 0.1% in degree of polarisation.
a) The position angle of polarisation, θ; b) the polarised flux
spectrum in mJy; c) the degree of polarisation as a percentage;
and d) the total flux spectrum in mJy. Note the large change in
polarisation position angle across the broad Hα emission line,
which reverses direction at the line peak. In polarised flux, the
broad emission line is redshifted with respect to the wavelength of
the peak in total flux. Adapted with permission from Macmillan
Publishers Ltd: Nature (S. Young et al., 450, 74), copyright 2007.
bright supernova discovery, the nature of this transient,
named UGC 4904-V1, became intriguing.
A global collaboration of astronomers analysed the images
containing the two transients using differential astrometry
of 21 nearby stars, and found that UGC 4904-V1 and SN
2006jc were indeed coincident to within the uncertainties.
So they decided to follow-up and study SN2006jc with a
10 • ING BIENNIAL R EPORT 2006–2007