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 early-type 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

Steps1. Close the Jackson and Wall loop

a. Get best luminosity functions + evolutionb. Get best beaming parameters

2. Guess emission line/continuum model3. Populate the universe with objects according to

the model4. 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 selection-induced correlations