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Dielectronic recombination and stability of warm gas in AGN
Susmita Chakravorty
Harvard University, Harvard-Smithsonian CfA
Ajit KembhaviMartin ElvisGary FerlandN. R. Badnell
The 17th International Conference on
Atomic Processes in Plasmas
Queen’s University, Belfast22nd July 2011
2008 MNRAS, 384L, 24
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What is an Active Galactic Nuclei : Its properties
Small Angular size
Highly luminous (≥galactic)
Milky Way ~ 1044 ergs/sec
AGN ~ 1042 – 1048 ergs/sec
Sun’s Diameter ~ 1.392 X 106 km
AGN ~ Size of a star
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What is an Active Galactic Nuclei : Its properties
Broad Band Continuum
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Radio far-IR optical EUV X-ray
Broad Band Continuum
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Broad Band Continuum
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Emission lines
in Optical
in Radio
Infrared
UV and X-rays
Gamma Rays
(Inverse Compton)
Edge on
Radio Galaxy
Type II Seyfert Galaxy
Type II Quasar
Type I Seyfert Galaxy
Type I Quasar
BL Lac Object
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Emission lines
in Optical
in Radio
Infrared
UV and X-rays
Gamma Rays
(Inverse Compton)
Edge on
Radio Galaxy
Type II Seyfert Galaxy
Type II Quasar
Type I Seyfert Galaxy
Type I Quasar
BL Lac Object
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Emission lines
in Optical
in Radio
Infrared
UV and X-rays
Gamma Rays
(Inverse Compton)
Edge on
Radio Galaxy
Type II Seyfert Galaxy
Type II Quasar
Type I Seyfert Galaxy
Type I Quasar
BL Lac Object
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0.1 pc
100 pc
Type II Seyfert Galaxy
Type II QuasarType I Seyfert Galaxy
Type I Quasar
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0.1 pc
100 pc
Type II Seyfert Galaxy
Type II QuasarType I Seyfert Galaxy
Type I Quasar
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Radio far-IR optical EUV X-ray
Broad Band Continuum
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Signatures of warm absorber
Absorption Edges in Soft X-ray Spectra
CV CVI OVII OVIII FeXVII NeX392 490 740 870 1260 1360 (eV)
C (V & VI) O (V - VIII) Fe (XVII - XXII)Ne (IX & X) Mg (XI & XII) Si (XIII - XVI)
(eV)
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Properties of the warm absorber
• Partially ionized gas in our line of sight to AGN
• Absorption features are blue shifted relative to optical emission lines, indicating outflow
• Column Density (NH) ~ 1022±1 cm-2
• Ionization Parameter ~ 10 – 1000 erg cm s-1
• Temperature ~ 105 K – 106.5 K
• Density (nH) ~ 109 cm-3 (105 - 1012)
• Distance from the source ~ 0.01 – 100 pc
= L/nR2
/T ~ (prad)ion/p
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Why do we care?
We need to understand warm absorber nature
• Mass loss rate is a substantial fraction of the accretion rate, or exceeds it.
• The X-ray warm absorber could coexists with a UV absorber.
• Distance from the source ~ 0.01 – 100 pc
• Is the Warm Absorber in thermodynamic equilibrium?
• If so, does the gas have multiphase nature?
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T
P
Stability Curve
= L/nR2
/T ~ (prad)ion/p
Curve – phase diagram
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CLOUDYhttp://www.nublado/org/
Inputs
Radiation Field
Geometry
Neutral Composition
Density
Thickness
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CLOUDYhttp://www.nublado/org/
ProcessBasic Assumption
Atomic processes reached time-steady state
Thermal balance achieved
Working principle
ij ji i ij
j i j i
nn R Source n R Sink 0
t
i i i 1 i 1e G
n(X ) (X ) n(X )n (X ,T)
Coll IC Ph C( ) / n
Inputs
Radiation Field
Geometry
Neutral Composition
Density
Thickness
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CLOUDYhttp://www.nublado/org/
Inputs
Radiation Field
Geometry
Neutral Composition
Density
Thickness
Output Thermal state & Ionic composition of cloud
Teq
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2-Phase medium
High temperaturelow densityphase
Low temperaturehigh densityphase
Stability CurveEach point in the curve have thermal
and ionic composition information
Stable
Stable
Unstable
= L/nR2
/T ~ (prad)ion/p
Curve – phase diagram
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Stability Curve
Important Heating and Cooling Processes
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Stability Curve
Important Heating and Cooling Processes
WA
WA
WA
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Stability Curve
Important Heating and Cooling Processes
BremsstrahlungCompton Cooling
Cooling by recombinationBremsstrahlung
Photoionization of metals
WA
Compton Heating
WA
WA
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C84 1993 to 1996(Reynolds – Fabian, ‘95)
&C07, 2007
Susmita Chakravorty et. al,
2008 MNRAS, 384L, 24
Dielectronic recombination and stability of warm gas in AGN
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C84 1993 to 1996(Reynolds – Fabian, ‘95)
&C07, 2007
0.070.22 0.46274C07
0.050.05 0.47245C84
Mlog(/T)log(/T)
~105K ~106K
Nphases5Version
Susmita Chakravorty et. al,
2008 MNRAS, 384L, 24
Dielectronic recombination and stability of warm gas in AGN
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He+1
Si+10, Si+11, Si+12
Fe+21, Fe+22, Fe+23
O+6, O+7
Fe+17 to Fe+25
Cause : Heating and Cooling agents
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Cause : Column Densities
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He+1
Si+10, Si+11
All of Fe, but Fe+21, Fe+22, Fe+23
It’s the cooling agents which make a difference
Cause : Column Densities
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Dielectronic recombination(the most likely candidate?)
Quantum mechanical calculations Experimental estimates
Revisited by Badnell and coworkers (2000 - 2007) Rates are substantially larger for quite a few ions.
The cooling agents are among the species analysed.
The differences in stability curves are due to these changes. It is therefore necessary to revisit older calculations.
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Dielectronic recombination(the most likely candidate?)
Quantum mechanical calculations Experimental estimates
Revisited by Badnell and coworkers (2000 - 2007) Rates are substantially larger for quite a few ions.
The cooling agents are among the species analysed.
The differences in stability curves are due to these changes. It is therefore necessary to revisit older calculations.
Savin et.al. 1999, ApJS, 123, 687
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Future directions
Extensive quantitative study looking for other possible causes.
Check the reliability at lower temperatures – still a very active domain of update in atomic data base.