Dielectronic recombination and stability of warm gas in AGN

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

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

What is an Active Galactic Nuclei : Its properties

Broad Band Continuum

Radio far-IR optical EUV X-ray



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

Emission lines

in Optical

in Radio

Infrared

UV and X-rays

Gamma Rays

(Inverse Compton)

Edge on

Radio Galaxy


Type II Quasar


Type I Quasar

BL Lac Object

Emission lines

in Optical

in Radio

Infrared

UV and X-rays

Gamma Rays

(Inverse Compton)

Edge on

Radio Galaxy


Type II Quasar


Type I Quasar

BL Lac Object

0.1 pc

100 pc


Type II QuasarType I Seyfert Galaxy

Type I Quasar

0.1 pc

100 pc


Type II QuasarType I Seyfert Galaxy

Type I Quasar

Radio far-IR optical EUV X-ray


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)

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

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?

Stability Curve

T

P

Stability Curve

= L/nR2

/T ~ (prad)ion/p

Curve – phase diagram

CLOUDYhttp://www.nublado/org/

Inputs

Radiation Field

Geometry

Neutral Composition

Density

Thickness


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


Inputs

Radiation Field

Geometry

Neutral Composition

Density

Thickness

Output Thermal state & Ionic composition of cloud

Teq

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

Stability Curve

Important Heating and Cooling Processes

Stability Curve


WA

WA

WA

Stability Curve


BremsstrahlungCompton Cooling

Cooling by recombinationBremsstrahlung

Photoionization of metals

WA

Compton Heating

WA

WA

C84 1993 to 1996(Reynolds – Fabian, ‘95)

&C07, 2007

Susmita Chakravorty et. al,

2008 MNRAS, 384L, 24


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


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

Cause : Column Densities

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

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.

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

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.

Education

Dielectronic recombination and stability of warm gas in AGN