X-ray spectroscopy Workshop – Cambridge (MA, U.S.A.) - Thursday, July 12 th 2007 On the origin of soft X-rays in obscured AGN Stefano Bianchi Matteo Guainazzi

Guainazzi et al Predicted starburst contribution Actual soft X-ray luminosity Turner et al ASCA The key to understand its nature is HIGH RESOLUTION SPECTROSCOPY soft X-ray excess The 'soft X-ray excess' is almost ubiquitous in Seyfert 2s and cannot be completely attributed to starburst emission

NGC1068 Kinkhabwala et al XMM RGS Strong emission lines dominates! No continuum  log(NH )<22.7

NGC1068 Kinkhabwala et al Diagnostic ratios on triplets AND higher order series lines confirm photoionization, excluding contribution from collisional plasma Important role of photoexcitation (resonant scattering: Band et al. 1990, Matt 1994, Krolik & Kriss 1995) Detection of narrow 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 Sako et al. 2000

Chandra HETGS Sambruna et al Circinus Schurch et al XMM RGS NGC4151

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 in sources 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 by XMM-Newton RGS CIELO-AGN Catalogue of Ionized Emission Line Obscured AGN Guainazzi & Bianchi, objects  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 Photoexcitation RRCs are: Common Common (detected in 40% o.t.s.) Narrow Narrow (  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= NGC1386 – z= Bianchi et al (+ 6 other objects) Where is this gas located? Circinus Smith & Wilson 2001 NGC4151 Yang et al 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 n e  r - , 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?

HSTChandra 110 pc 3 pc In the immermost 110 pc: low luminosity AGN: L X ≈10 39 erg s -1 young stellar cluster: L X ≈6×10 38 erg s -1 NGC4303 Jiménez-Bailón et al NGC7130 Levenson et al What about the starburst contribution?

Empirical diagnostic diagram based on high resolution spectroscopy Guainazzi & Bianchi 2007 AGN -Total L O ≥10 40 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 Conclusions CIELO unveils a criterion to discriminate between AGN- and starburst-dominated sources on the basis of the OVII(f)/OVIII ratio