The origin of the Broad Ionization Distribution

in Warm Absorbers

Jonathan Stern

Based on: Stern, Behar, et al. 2014 (MNRAS..445..3011)

Outline

1. Observations: the broad ionization distribution of warm absorbers

2. Model: compression by radiation pressure

3. Comparison of model with observations

Intro: Warm Absorbers

Blueshifted absorption features

(𝑣~100 − 1000 km s−1)

seen in X-ray spectra of AGN

Open Questions: • Extended or localized outflows?

• How are the outflows accelerated?

• What is the outflow impact on the host galaxy?

Holczer+2007, IRAS 13349+2438, 300ks HETGS

Ion 𝑁ion/1016 cm−2

high-res spectrum: Column densities (𝐅𝐞+𝟎 − 𝐅𝐞+𝟐𝟑):

A Clue: the Broad Ionization Distribution

A Clue: the Broad Ionization Distribution

Together with Fe column measurements and assuming 𝑍~𝑍⊙, we get:

Why do all objects have 𝑑𝑁

𝑑log 𝑈≈ 3𝑥1021𝑈0−0.4 ?

Behar (2009), Holczer & Behar (2012)

A Clue: the Broad Ionization Distribution

𝑃gas =𝐿

4𝜋𝑟2𝑐1 − 𝑒−𝜏

…some algebra…

→𝑑𝑁

𝑑log𝑈= 𝜎−1 ∙

𝑇

104K∙

𝑈

0.03

−1

∙ 1 −d log 𝑇

d log𝑈

→𝑑𝑁

𝑑log 𝑈~ 8𝑥1021

𝑈

0.03

0.03

cm−2

Compression by Radiation Pressure (RPC)

can be deduced from photoionization equilibrium

can be deduced from thermal equilibrium

8-10 free parameters with constant density models

0(!) free parameters with RPC

Stern et al. (2014)

RPC: analytic approx.

RPC: Comparison with Observations

RPC: CLOUDY

direct fit to ion column densities

(TITAN)

NGC 3783

Goosmann et al. (2016)

cold RPC solution hot RPC solution data

RPC: Comparison with Observations

RPC predicts

d𝐿

d log𝒰∝ 𝒰−0.9

as observed!

NGC 1068

Ogle et al. (2003)

d𝐿

d log𝒰∝ 𝒰−1

RPC: Comparison with Observations

Summary and Implications

Ionization distribution in Warm Absorbers suggests compression by radiation pressure

Implications:

• Small outflow filling factors and large density gradients

• Dominant force on outflow is radiation pressure

• Other sources of energy and momentum (shocks, magnetic) likely sub-dominant

• Suggests 𝑝 < 𝐿/𝑐