Modelling the Broad Line Region

Andrea Ruff

Rachel Webster

University of Melbourne

Outline

The primary goal is to model the geometry, dynamics and physical conditions of the BLR

What do we know about the BLR Line ratios, stratification of ionisation

Modelling with Cloudy A simple cloud distribution

Simulations over large parameter space

Further Work

Structure of Quasars

The region is too small to be spatially resolved with a telescope Peak Quasar population

z~2 (~10 billion yrs ago)

What is the BLR?

Regions with no BLR gas, but what are the angles?

Quasar spectrum

Lyα

CIV

CIII]NV

About the BLR

Photo-ionised gas (T from line ratios)

Non-thermal broadening The gas is moving with a high velocity

Up to 0.1c

Variations in BL fluxes in response to the continuum (point like) Gas is close to the central BH, but also

distributed over a large radius

Broad Emission Line flux ratios

Quasars vary in Luminosity by up to 4 dex The same emission lines are seen In the same approximate ratios

Why? T(photo-ionisation equilibrium) ~ 104K?

Peterson, 2006

Unlikely, not reflected in simulations

Something else is causing this

Fluxes and time delays

Line Relative Emission Time Delay (lt days)

Lyα 1216Å 1.00 2

C IV 1549Å 0.4-0.6 10

C III] 1900Å 0.15-0.3 20

Mg II 2798Å 0.15-0.3 44

Data from: Baldwin et al. (1989), Peterson, Francis et al. (1991) for Seyferts

Dynamics of the BLR

Keplarian rotation about the central BH

Assumes gas is from the accretion disk

FWHM is larger for higher E ionisation lines

An outflow has also been suggested by asymmetries in BL profiles

Line separations support this

MHD on small scales

Radiative driving (continuum and line)

Consequences of an Outflow

The optical depth will be modified Castor (1974)

The optical depth depends on the velocity gradient

This changes not only the emitted flux, but also the

shape of emission lines

The rotation will also influence the line profile

Modelling the BLR

Numerical simulation

Cloudy, Gary Ferland and associates “Spectral simulations for the discriminating astrophysicist since 1978”

Emission is calculated from a set of initial conditions

Gas density, distance from source, source brightness and shape, metallicity, NH, velocity

A Simple Outflow

Using mass conservation:

This gives a power law: Simulations show that

The power law index is way more important than specific cloud conditions

Arbitrary power law Nc α rβ

Line density (cm-3) β=1 β=2 β=3

C IV 1549 nH=109 0.451 0.330 0.144

nH=1010 0.518 0.243 .0422

nH=1011 0.760 0.244 .0205

Mg II 2798 nH=109 .0907 0.210 0.293

nH=1010 0.115 0.327 0.448

nH=1011 0.117 0.432 0.614

Parameter Space: EW

EW: reprocessing efficiency How efficiently the line is produced from the

continuum radiation (at 1216Å)

Can get line luminosity from appropriate integration:

Baldwin et al. (1995)

Where f(r) and g(n) are cloud covering fractions

Also gives emission response as a fn of r

r2

These plots show the reprocessing efficiency

3,249 different BLR configurations

CIV collisionally excited

Also give emission response as a function of r

Integration gives line flux

The terms in the integration need to be determined using hydrodynamics

density

The integration will also give emission as a function of radius

Constant density model

nH = 1010 cm-3

The chosen hydrogen density will influence this if there is a radial dependence on velocity

2 lt days

10 lt days 44 lt days

Accuracy of a single density model

Further complexity is required

LOC model (Baldwin et al. 1995) Argues that there is a conglomeration of

many different density clouds

Given the distance scales of the BLR, would nH α r-γ be expected? This dependence should be considered

Summary

The gas distribution is important in calculating emission line ratios

The reason for consistent ratios over 4 orders of luminosity has been established

Using Cloudy: Simulate relative line intensities

Radius of emission

This model requires a good description of the flow

Further Work

Further investigation of free parameters

Incident continuum, metallicity, turbulence, velocity

Need to make a model!

This model will give line ratios, line shapes, timing predictions

Thanks

Questions?