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Unification -- 2
Where next?
Recap of current status
• Emission from nuclear relativistic jets is
important in all radio-loud objects.
• Axisymmetric dust extinction is probably
important in all AGN.
Orientation is crucial to the appearance of
an AGN. “The consensus Model”
 Details uncertain (but perhaps less interesting)
The AGN Paradigm
Annotated by M.
Voit
Interesting Questions
• What gives rise to diversity of properties we
observe?
– Unification by orientation takes care of some.
• But what about the radio quiet/radio loud
dichotomy?
• What about the huge spread in synchrotron peak
frequencies?
• Can we use beaming models to probe the structure
of the inner regions of AGN?
Jackson and Wall approach
(N.B. Carole Jackson not Neal)
• Jackson and Wall (MNRAS,304,160) try and
“close the loop”. Orr and Browne and others have
used simple beaming models to predict source
counts as a check of the plausibility of the
beaming models.
• Jackson and Wall use the beaming model for
different populations to predict their relative
contributions to source counts, compare with
observations and then adjust the model parameters
to improve the fit.
– Potentially an exciting approach if the AGN
populations can be described by simple model.
More Jackson and Wall
• The primary motivation is to understand
populations – their relative numbers and
their cosmological evolution.
• Refining beaming model parameters comes
as a bye-product.
Ingredients of the JW model
• FR1 and FR2 unification
– Low excitation FR2s are included as
contributors to the BL Lac population
– Beaming model parameters
• Cosmological evolution of each population
• A small population of starburst galaxies
• Monte Carlo approach
Input information
• Multi-frequency source counts
• Optical identifications for strong sources
• Redshift distributions for strong sources
Results
• A satisfactory fit can be obtained with
“reasonable” beaming parameters
• Predictions are made for the mix of
different objects in low flux density
samples.
– Better data are now available which are not
fully consistent with predictions but I am sure
the model can be refined
Greater Unification– Black hole
Mass
• Unification is about simplification. A most
remarkable simplification of our view of galaxies
is the emergence of the tight relationship between
the bulge mass/velocity dispersion and black hole
mass. (How this relates to the formation of galaxies is beyond the
scope of this talk.)
• Every galaxy has an engine capable of making it
an AGN. (It probably was one once!)
BH Mass vs. Galaxy Bulge Mass
There is a relationship between BH mass and bulge
luminosity. And an even tighter relationship with the
bulge velocity dispersion. M(BH) ~ 10-3 M(Bulge).
Ferrarese & Merritt 2000, ApJ, 539, L9
The origins of diversity
• Neglect the question of what makes some things
radio-loud.
• Radio loud objects are hosted by massive earlytype galaxies => not much dispersion in BH mass
• Fuelling rate is left as the major factor to account
for the dispersion in luminosity.
– The similarity of the high luminosity AGN
cosmological evolution and the star formation rate as of
epoch fits this simplification.
– The presence of an AGN may simply be telling us that
there is star formation activity going on in the bulge.
Is Fuelling rate the
answer to
everything?
• Fossati et al and Donato et al
present evidence that blazars
SEDS depend only on
luminosity.
• I have been pushing the view
that all radio-loud cores are
basically of the same type
• Luminosity depends on fuelling
which means that together we
have a self-consistent story
• Fuelling is the answer
• maybe
The question of fuelling
• Ghisellini et al, argue that, as the photon flux from
the accretion disk increases (with
fuelling/luminosity), these are more likely to be IC
scattered by the jet electrons, thus removing the
highest energy electron preferentially from the jet.
• This is a natural physical explanation for the
Fossati et al correlation.
– I like this simple picture and hope it’s true
– I am not convinced by the Fossati et al result
The structure of Radio-loud AGN
• By looking how emission line properties
change with orientation we should learn
more about the inner regions of radio-loud
AGN; i.e.the distribution of emission line
gas and dust.
– E.g. because the FWHM of H-beta in quasars
was smaller in the most core-dominated (those
pointing at us) Wills and Browne argued that
the BLR was disk-like. It might even be true!
Correlations for quasars
• H-beta equivalent width does not change with R
• [OIII] EW decreases with increasing R
• High R quasars are brighter than low R for a given
radio flux (Not extra non-thermal continuum).
• R5000 anti-correlates with H-beta FWHM, as does R
• Etc.
• Some correlations suggest that the continuum is isotropic,
others the opposite. Similarly for H-beta emission.
Result -- confusion
How to make progress?
• We are looking for simple underlying
pictures which may or may not exist.
• There is are a wealth of observational data,
lots of potentially important correlations but
how do we make sense of what’s going on?
• If blazars are anything to judge by, and in
many ways they are the simplest systems,
we are plagued by selection effects.
Building virtual universes
• Given the multitude of parameters we have
measured for AGN and the different ways samples
are selected, it is difficult to separate what’s due to
selection and what’s telling us about astrophysics.
• I would suggest that an extension of the Jackson
and Wall approach is a good way to go.
• Populate a virtual universe with objects according
to some very simple model which includes a
plausible cosmological geometry
Steps
1. Close the Jackson and Wall loop
a. Get best luminosity functions + evolution
b. Get best beaming parameters
2. Guess emission line/continuum model
3. Populate the universe with objects according to
the model
4. Select objects from the virtual universe in the
same way that observational samples are
selected.
5. Compare real and virtual samples.
6. Adjust model. (Do not change beaming parameters plus
luminosity functions.)
Advantages
• Simulates the process one tries to do in
one’s head
• It sorts out the selection effects from the
real astrophysics
• Can be used for the large numbers of
objects in modern databases.
Conclusions
1. Historically unified models are built on results
from VLBI
2. There are exciting possibilities for wider
unification
a. Explaining non-thermal SEDs
b. Finding out about the geometry of AGN inner regions
3. Need to develop tools to deal with selectioninduced correlations