X-ray Obscured AGNs

1. X-ray Obscured AGNs E. Piconcelli, F. Fiore, G. Lanzuisi (OAR) S. Bianchi (Roma3) M. Guainazzi (XMM-Newton SOC / ESA) G. Miniutti (APC, Paris) M. Chiaberge (STScI) Piconcelli et al. 2007c, A&A, in press Piconcelli et al. 2007b, A&A, 473, 85 Piconcelli et al. 2007a, A&A, 466, 855 Bianchi et al. 2007, MNRAS 374, 697 Reviews: Maiolino & Risaliti (astro-ph/0707709) + Fabian (astro-ph/0304122)

2. Type 1  Type 2 Type 1: optical broad lines / X-ray unobscured Type 2: optical narrow lines / X-ray obscured

3. X-ray spectra of absorbed AGN XMM, Chandra, ASCA, Suzaku, BeppoSAX BeppoSAX, Suzaku, Swift-BAT, Integral NH = 1023 cm-2 NH = 5 1024 cm-2 Compton Reflection Photoabsorption cross-section E-3.5 ≈ Compton cross-section at 10 keV NH(Compton-thin) <NH =1.5 1024 cm-2< NH(Compton-thick)

4. Properties of X-ray absorber in AGN Physical Statistical Cosmological NH Distribution vs Flux NH Distribution vs Lum NH Distribution vs AGN Type NH vs redshift Evolution CXB Column Density NH Location Geometry Covering fraction Ionization state X-ray vs IR/Opt Risaliti+99 Fiore 06

5. Changing-look AGNs:A challenge for the classical torus The most common Unified Model locates the absorption in a dusty torus at pc-scale from the SMBH A single homogeneous cylindrically-symmetric absorber ….but is it the whole story? NO! Pieces of evidence: Risaliti+02 found that 23/24 Sey2s showed Nh variability by a factor of 3 on timescale of months… …too fast to be due to Keplerian motion at pc radii! Guainazzi+03: discovered the “Phoenix Galaxy” (UGC 4203) Matt+03: “Changing look: from Compton-Thick to Compton-thin, or the rebirth of fossil AGN” Elvis+04: NH variation in the Sey2 NGC4388: absorber on a few 10-2 pc radii scale Risaliti+05,+07: NGC 1365 - Spectacular transitions from C-thin to C-thick and back to C-thin in 3 obs. performed in 4 days! Obscuring cloud is located at ~10-3 pc (i.e. 300 RG) X-ray source size DS<1014 cm, 10 RG

6. X-ray observations of spectral state transitions Ngc 1365 - Risaliti+07 Ngc 7674 - Bianchi+05 Ngc 4939 - Guainazzi+05

7. NGC 7582: AGN switch-off Piconcelli+07 •Dramatic spectral transition: XMM caught NGC 7582 in a “reflection-dominated” phase, measuring the lowest continuum flux level ever in 2005! •Very complex X-ray spectrum: combination of a heavily absorbed (NH ~1024 cm-2) power law and reflection component BOTH obscured by an additional absorber of 4  1022 cm-2. • NH variation: the thicker abs. increased by a factor of 2 between 2001 and 2005

8. NGC 7582: Origin of the soft X-ray emission in obscured AGN Chandra and XMM-Newton have provided unprecedented insights into the nature of the soft X-ray emission in AGN • Extended emission (hundreds of pc) Soft X-ray emission coincident in extension and overall morphology with the NLRBianchi+06 • Photoionized (single?) plasma with kT ~ few eV High resolution spectra taken with the grating spectrometers on-board XMM and Chandra found that soft X-rays carry unambiguous signatures of photoionized gas: (I) “narrow” Radiative Recombination Continua (II) large ratios between forbidden line He-like of H triplets and H-like LySako+00, Kinkhabwala+02, Guainazzi & Bianchi 06 Soft X-ray emission is due to reprocessing of the primary emission (~3%) Guainazzi+07 ACIS-S Chandra: 0.1-2 keV HST/WFPC2: [OIII] 5007l Piconcelli+07

9. Things to bring home (1) •Changing-look AGNs reveal a complex scenario whereby the obscuring gas is largely inhomogeneous in space and/or time. •Compton-thin and Compton-thick absorbers coexist in the same source •Large NH suggest that the Compton-thick absorber is located at few light-days from the SMBH •Compton-thin (NH <1024 cm-2) absorber associated with host galaxy dust lanes with large covering factors •Soft X-ray emission spatially extended along the [OIII] ionization cone •Soft X-ray spectrum dominated by a wealth of emission lines.Both AGN-photoionzation and “local” photoionization due to gas heated by high-speed shocks driven by nuclear outflows (radio jets?) in the ISM are viable mechanisms

10. Obscured quasars (QSO 2s) QSO 2s are the luminous counterparts (LX > 1044 erg/s) of the local Sy2 galaxies with NH>1022 cm-2 Crucial (and necessary!) component of AGN Unification theories and of models explaining the Cosmic X-ray and IR background by the growth of obscured SMBHs throughout cosmic history. But….Where are they?? QSO 2s have been rarely detected (~10%) even in the deep X-ray surveys!! Two possible physical explanations:  The receding torus model (Lawrence 91; Simpson 05): The location of the inner wall of the torus is set by the distance from the active nucleus at which the dust sublimates In QSOs the major phase of BH growth may be completely obscured and the accretion close to the Eddington limit High-L QSOs may have the power to remove via nuclear winds a significant fraction of the obscuring matter (Silk & Rees 99, Hopkins+05) • Selection effects: • QSO 2s at z>1 are expected to have high X/O (optical emission probes the rest-frame UV) ~25% of XMM/Chandra sources show X/O>10 and R>25, e.g. Fiore+03 Deep spectroscopy indeed found high-z, X-ray obscured QSOs (Mainieri+05, Maiolino+06) Akylas+06 …What about Compton-thick QSO2s? (~40-50% of all Sey2s in the local Universe) Evidence for C-thick QSO2s by X-ray spectroscopy still remains ambiguous (i.e. IRAS 09104+4109, Piconcelli+07b)

11. Towards a complete census of SMBHs: The QSO 2s hunt Alternative approaches wrt the pure X-ray selectionMulti-wavelength selection criteria The IR band is promising since absorbed AGN opt/UV/X-ray light should be isotropically re-emitted by the obscuring material at these frequencies. Martinez-Sansigre+05,+07 (combination of radio + MIR data) claimed the discovery of a distant, optically-faint QSO2 population with density ~ optically-bright QSO population Houck+05 + Weedman+06 found that dozens of sources with 24m/I >100 and strong Si absorption features likely are QSO-powered ULIRGs at 1.7<z<2.8 Polletta+07 presented results from a sample of sources with z>1, MIR/O>400 and F(24m) >1 mJy: 5 out of 11 having X-ray data show NH>1023 cm-2 Fiore+08: 135 Sources with MIR/O>1000 R-K>4.5 (HST+VLT+Spitzer+Chandra data on the Chandra Deep Field South) 22 sources detected by Chandra: hardness-ratio (i.e. X-ray color-color) analysis indicates NH>1022 Stacked spectrum of the remaining ones shows … {

12. QSO2s in SWIRE sources with extreme mid-IR/Opt flux ratiosLanzuisi,Piconcelli, Fiore 2008 We selected a sample of 44 eXtreme MIR/O ratios galaxies (XMOGs) MIR/O>2000 and F(24m)>1.5mJy AIM: Confirmation via X-ray spectroscopy that XMOGs harbor high-z QSO2s RESULTS: 23 out of 44 sources have positive X-ray detection 35-50% of the XMOGs are QSO2s 90% of the XMOGs are obscured AGN 6/23 have spectroscopic redshift (0.7<z<2.5) Photometric redshift for all the sample (0.5<z<3.8) consistent withRowan-Robinson+08 Proxies of high obscuration and high luminosity: MIR/O>2000 and F(24m)>1.5mJy (e.g. Lacy+04; Polletta+06; Fiore+08) Given the low surface density of these luminous sources, a sampling of a large area is necessarily required  Sources have been selected from the ~50 sqdeg
SWIRE survey. We selected a sample of 44 eXtreme MIR/O ratios galaxies (XMOGs) AIM: Confirmation via X-ray spectroscopy that XMOGs harbor high-z QSO2s

13. Things to bring home (2) •Only 50% of the CXB has been resolved at >8 keV. A missed population of heavily obscured AGNs is required to fill the gap •Is the anticorrelation between absorbed AGN and luminosity real or just a selection bias? •What’s on at high z? QSO2s are the dominant sub-population of quasar? • Mid-IR colors selection is promising to collect large samples of highly obscured QSO 2s largely missed in traditional optical/X-ray surveys •X-ray spectroscopy of XMOGs (MIR/O>2000 and F(24m)>1.5mJy) reveals that most of them are QSO 2s at z>1 •Future Work: XMM-Newton/Chandra deep exposures of the best Compton-thick QSO candidates