The Size, Structure & Ionization of the Broad-Line Region in NGC 3227

and NGC 4051

Nick Devereux (ERAU)

Emily Heaton (ERAU)

May 22nd, 2013

Naples, Italy

NGC 3227D = 21 Mpc

Low luminosity, Lbol/Ledd < 10-3

NGC 3227D = 21 Mpc

Low luminosity, Lbol/Ledd < 10-3

Current paradigm is that BLR is small

NGC 3227D = 21 Mpc

Low luminosity, Lbol/Ledd < 10-3

Current paradigm is that BLR is small

New result: the reverberation radius marks just the inner radius of a much larger volume of ionized gas

BH mass in NGC 3227 is constrainedby gas kinematics, reverberation mapping &

stellar velocity dispersion;

M = (7 - 20) x 106 M

Davies et al., 2006, ApJ 646, 754 Hicks & Malkan 2008, ApJS 174, 31 Denney et al. 2010, ApJ 721, 715

HST spectra showing the time variable broad H emission line.

The broad Hline in NGC 3227 with the narrow lines subtracted illustrating the line profile expected for the inflow

model.

There are good reasons to consider an inflow

• All AGN pundits agree that AGN activity is fueled by gas flowing into a super-massive black hole.

• Stellar mass loss provides an abundant source of fuel.

• Since only zero angular momentum gas can free-fall into the BH, the inflowing gas has no rotation by definition.

Visualization of the Inflow

Gas is in spherically symmetric free-fall, v(r) = √ 2 GM(r)/r

Mass, M(r) includes central MBH + stars

Number density of inflowing points, N(r)

Mass inflow rate, dm/dt 4πr2 N(r) v(r)

Steady State inflow, dm/dt f(r) which implies N(r) r-3/2 since r2 r-3/2 r-1/2 f(r)

Consequently, there are just 2 free parameters to model the shape of the broad emission line –

the inner and outer radius of the ionized volume emitting Balmer lines.

Inflow Model Parameters

The broad Hline in NGC 3227 with the narrow lines subtracted illustrating the line profile expected for the inflow

model.

Uncertainties on the inner and outer radii are ~ 20% - 30%

Inner radius, ri

Out

er r

adiu

s, r

oΧ2 Surface

the inner radius uniquely defines the full width at zero intensity of the broad Hline

the inner radius uniquely defines the full width at zero intensity of the broad Hline

The inner radius of theinflow coincides with the reverberation radius!

Fvar ~8%

Suggesting a new way to compute BH Masses using reverberation radii

using the free-fall equation; M• = R ΔV2/2G

where ΔV is the half-width at zero intensity and R is the reverberation radius.

This method negates the large ~ 5.5 correction factor, f, required for the virial product advocated by Peterson et al. (2004, ApJ 613, 682)and Onken et al., 2004, ApJ 615, 645.

See Devereux & Heaton (2013), ApJ in press for more details.

Photoionization Model

Analogous to that developed for HII regions by Osterbrock.

The only difference is that the ionization is provided by the AGN

Basic concept: Ionization balanceNumber of ionizing photons = number of recombinations

Photoionization Model Results

The outer radius of the BLR is ionization bounded.

The outer radius of the BLR is ionization bounded.

Photoionization Model Results.

Photoionization Model Results.

Electron density is low

Ionization parameteris high

The size of the BLR depends, at least, on

• the neutral H gas density, nH

• ionizing photon rate, Nion

•For a given Nion,

Low nH Large BLR “narrow line” NLS1, NGC 4051

High nH Small BLR “broad line” S1, NGC 3227

Kaspi et al., 2005, ApJ 629, 61

Please visit Poster # 15 by Emily Heaton!

In Summary….

• The line profile modeling shows that the reverberation radius marks just the inner radius of a much larger volume of partially ionized gas. Consequently, the BLRs of LLAGNs are actually much larger than previously believed!

 

 

In Summary….

• The line profile modeling shows that the reverberation radius marks just the inner radius of a much larger volume of partially ionized gas. Consequently, the BLRs of LLAGNs are actually much larger than previously believed!

 

 

• The photoionization modeling shows that the reverberation radius marks a transition from partially ionized gas to completely ionized gas as the AGN is approached.

 

In Summary….

• The line profile modeling shows that the reverberation radius marks just the inner radius of a much larger volume of partially ionized gas. Consequently, the BLRs of LLAGNs are actually much larger than previously believed!

 

 • The photoionization modeling shows that the reverberation

radius marks a transition from partially ionized gas to completely ionized gas as the AGN is approached.

 • Collectively, a spherically symmetric inflow is able to

mimic the broad emission line profile shape. Further, the inner radius of the inflow coincides with the reverberation radius, suggesting a new way to compute BH masses using the free-fall equation.

Future Workwill be to populate this diagram with approximately 24 additional AGNs listed in Peterson et al. (2004, ApJ 613, 682).

Backup Slides

Cloudy thinking?

Our perception that the electron density, n, is high > 109 cm-3 is based primarily on Cloudy (Ferland et al., 1988, PASP, 110, 761).

The problem with Cloudy is that it models the BLR as a single slab of fixed column density, NH = 1023 cm-2, which it certainly is not!

From which it follows that if r_BLR is of the order of 1017 - 1018 cm, then, given the fixed column density, n ~ must be of the order of 105 - 106 cm-3, not > 109 cm-3, predicted by Cloudy for certaindensity sensitive emission line ratios.

Condition for a radiatively driven outflow,

κL/4cG > M

Where κ is the Thompson scattering opacity

For NGC 3227, the condition is not satisfied by 2 orders of magnitude!

ie. the AGN in NGC 3227 radiates substantially below the Eddington luminosity limit.

Radiative outflow - not possible given the low luminosity of the AGN

Outer radius of the inflow ~ 90 lt-days.

Inner radius of the inflow ~ 3 lt-days and coincides with the reverberation radius (Denney et al. 2010, 721,715).

Inflow Gas Number Density, n > 106 cm-3 at the reverberation radius

Inflow Filling Factor ~ 1

Mass Inflow Rate ~ 2 x 10-2 M /yr.

Physical Properties of the Broad Line Regionin NGC 3227

Inflow Properties