The Size, Structure & Ionization of the Broad-Line Region in NGC 3227 and NGC 4051
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Transcript of The Size, Structure & Ionization of the Broad-Line Region in NGC 3227 and NGC 4051
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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
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NGC 3227D = 21 Mpc
Low luminosity, Lbol/Ledd < 10-3
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NGC 3227D = 21 Mpc
Low luminosity, Lbol/Ledd < 10-3
Current paradigm is that BLR is small
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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
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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
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HST spectra showing the time variable broad H emission line.
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The broad Hline in NGC 3227 with the narrow lines subtracted illustrating the line profile expected for the inflow
model.
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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.
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Visualization of the Inflow
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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
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The broad Hline in NGC 3227 with the narrow lines subtracted illustrating the line profile expected for the inflow
model.
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Uncertainties on the inner and outer radii are ~ 20% - 30%
Inner radius, ri
Out
er r
adiu
s, r
oΧ2 Surface
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the inner radius uniquely defines the full width at zero intensity of the broad Hline
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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%
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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.
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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
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Photoionization Model Results
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The outer radius of the BLR is ionization bounded.
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The outer radius of the BLR is ionization bounded.
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Photoionization Model Results.
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Photoionization Model Results.
Electron density is low
Ionization parameteris high
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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
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Kaspi et al., 2005, ApJ 629, 61
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Please visit Poster # 15 by Emily Heaton!
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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!
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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.
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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.
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Future Workwill be to populate this diagram with approximately 24 additional AGNs listed in Peterson et al. (2004, ApJ 613, 682).
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Backup Slides
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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.
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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
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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