X-ray spectroscopy Workshop – Cambridge (MA, U.S.A.) - Thursday, July 12X-ray spectroscopy Workshop – Cambridge (MA, U.S.A.) - Thursday, July 12thth 2007 2007

On the origin of soft X-rays On the origin of soft X-rays in obscured AGNin obscured AGN

Stefano BianchiStefano Bianchi

Matteo GuainazziMatteo Guainazzi

Guain

azz

i et

al. 2

00

5

Predicted starburst contributionA

ctu

al

soft

X-r

ay l

um

inosit

y

Turner et al. 1997

ASCA

The key to understand its nature isHIGH RESOLUTION SPECTROSCOPY

The 'soft X-ray excesssoft X-ray excess' is almost ubiquitous in Seyfert 2s and cannot be completely attributed to starburst emission

NGC1068

Kinkhabwala et al. 2002

XMM RGS

Strong emission lines dominates!No continuum log(NH )<22.7

NGC1068Kinkhabwala et al. 2002

Diagnostic ratios on tripletsAND

higher order series linesconfirm photoionization, excluding

contribution from collisional plasma

Important role of photoexcitation(resonant scattering:

Band et al. 1990, Matt 1994, Krolik & Kriss 1995)

Detection ofnarrow

Radiative Recombination Continua (RRC)

=>Low temperature gas

=>Photoionization

XMM-Newton 190 ks combined RGS spectrum

The high resolution

spectrum of Mrk3 is

unambiguously produced in a photoionized

gas:

-K lines dominant over

Fe L-RRCs

Resonant scattering is important:

-Fe L 3d-2p/3s-2p ratio

-K resonant/ forbidden ratio

Mrk3

Bianchi et al. 2006

Sako et al. 2000

Chandra HETGSSam

bru

na e

t al. 2

001 Circinus

Sch

urch

et a

l. 2004

XMM RGSNGC4151

What about the other Sy2s?

Most RGS spectra of Sy2s are dominated by emission lines with low or no continuum

Often, most of the ‘soft excess’is concentrated in single, very strong lines

which can be easily detected even insources with very low SNR spectra

Guainazzi & Bianchi, 2007

We produced the first catalogue of soft X-ray emission lines in a sample which includes all the type ≥ 1.5 AGN observed

byXMM-Newton RGS

CIELO-AGNCatalogue of Ionized Emission Line Obscured AGN

Guainazzi & Bianchi, 2007

69 objects<F0.1-2 keV> 10-13 cgs

OVIII Lyα detected in 50% of the sample OVII triplet in 40%

Many other lines from O, Fe, C, Si, Mg,

Ne, N detected in 15%

Guainazzi & Bianchi, 2007

CIELO confirms the results derived from the analysis of the brightest

sources Strong higher order lines

PhotoexcitationRRCs are:CommonCommon (detected in 40% o.t.s.)

NarrowNarrow (10 eV)

Photoionization

The stacked spectrum of

all the objects with

good SNR included in

CIELO confirms

these results

Main features (e.g. OVII and OVIII lines) are

also recovered in the stacked spectrum of

poor SNR objects

(~60% of the catalog)

NGC3393 – z=0.0125

NGC1386 – z=0.0029

Bia

nch

i et

al. 2

006

(+

6 o

ther

obje

cts)

Where is this gas located?

Circinus

Sm

ith &

Wils

on 2

00

1

NGC4151

Yang e

t al. 2

00

1

A close association between the soft X-ray emission and the NLR (traced by [OIII]) is observed both on large and small scale

The comparison between the Chandra and the HST images shows that the [OIII]/soft X-ray ratio is fairly constant along

with the radius, up to hundreds of pc. Photoionization models reproduce this behavior if ner-, with 2 (i.e. constant

ionization parameter). This is in agreement with NLR emission line ratios

(e.g. Kraemer et al. ’00, Kraemer & Crenshaw ’00, Bradley et al. ’04, Collins et al. ‘05).

Bianchi et al., 2007

What is this gas?

HST Chandra

110 pc

3 pc

In the immermost 110 pc:• low luminosity AGN: LX≈1039 erg s-1

• young stellar cluster: LX≈6×1038 erg s-1

NGC4303Jiménez-Bailón et al. 2003 NGC7130

Levenson et al. 2005

What about the starburst contribution?

Empirical diagnostic diagram based on high resolution spectroscopy

Guainazzi & Bianchi 2007

AGN

-Total LO≥1040 erg s-1

-OVII/OVIII≥1

So… AGN or starburst?

STARBURST

OVIII/OVII excess is NOT

coincident with star formation regions!Bianchi et al., 2007 NGC7582

… of course this is too simple

High-resolution spectroscopy IS fundamental to understand the physical properties of the gas in the AGN circumnuclear environment (as high-resolution imaging IS

fundamental to unveil its true location)

In obscured AGN, CIELO unveils mounting evidence for

Dominant role of AGN-photoionization,

Important role of resonant scattering,

Broadly constant ionisation parameter ...

on scales as large as a few hundreds parsec

ConclusionsConclusions

CIELO unveils a criterion to discriminate between AGN- and

starburst-dominated sources on the basis of the OVII(f)/OVIII

ratio