Luminous obscured quasars in the HELLAS2XMM survey: the Spitzer perspective

Luminous obscured quasars in the HELLAS2XMM survey: the Spitzer perspective Cristian Vignali Dipartimento di Astronomia, Universita`degli Studi di Bologna F. Pozzi, A. Comastri, C. Gruppioni, L. Pozzetti, M. Mignoli, C. Lari, G. Zamorani, M. Brusa & The HELLAS2XMM collaboration

Radio-quiet quasars Radio-loud quasars The culprit … Who inspired this work … Elvis et al. 1994

…and some recent results … Richards et al. 2006

Talk outline • The importance of obscured AGN: the X-ray view • Why Spitzer? • Sample selection: luminous, obscured quasars in the HELLAS2XMM survey and KS-band morphology of their hosts • A quick look at the SpitzerIRAC and MIPS data • Broad-band spectral energy distributions using IRAC+MIPS24 data: first results • Physical properties of the X-ray selected obscured quasar population from HELLAS2XMM: bolometric corrections, BH masses, and Eddington ratios Mission impossible: all in 10 minutes!

The importance of obscured AGN: the X-ray view • A large fraction of the accretion-driven energy density in the Universe is obscured by dust and gas (e.g., Fabian 1999) • Ingredient of the X-ray background synthesis models (e.g., Comastri et al. 1995; Gilli, Comastri & Hasinger 2007)  the high-luminosity, obscured AGN population (Type 2 quasars), expected on the basis of Unification schemes, only partially found • Obscured phase of the AGN growth linked to the host galaxy formation?

Why Spitzer? • The nuclear emission is re-processed in the IR band (by the dusty torus envisaged by the model?), less affected by extinction • Spitzer provides coverage over the 3.6-24 μm wavelength range (and also at 70 and 160 μm is some cases) • IR emission important to compute the resulting bolometric luminosity of obscured, luminous AGN through their SEDs REQUIRED: removal of the galaxy contribution

Sample selection: obscured quasarsfrom the HELLAS2XMM survey Mignoli et al. 2004 • SAMPLE: HELLAS2XMM • F2-10 keV >10-14 erg cm-2 s-1 over 1.4 deg2 • Optically faint (R>24) sources with • no optical identification • high X-ray-to-optical flux ratio • (X/O>10) sources with indications • of X-ray obscuration ISAAC KS-band follow-up • ALL bright in the KS band • All have R-KS>5 Extremely Red • Objects (EROs), some are extreme • Most have elliptical profiles, two are • point-like (Mignoli et al. 2004)

High X/O population unveiled also by Chandra ≈10-20% of the sources detected in the X-ray surveys have X/O>1 Log (X/O)>1 e.g., SEXSI survey: Eckart et al. 2006

EROs BLAGN X/O>10 similarly, in the COSMOS survey… acs mips 24 Lx=1045 z=1.59 Point-like + steep PL SED acs mips 24 Lx=1044.7 z=1.2 Extended + galaxy-dominated SED (Civano et al., in prep.) a significant fraction of EROs is associated with X/O>10 sources EROs have larger X/O than broad-line AGN

What about the source redshifts? Estimated redshift range: 0.8<z<2.4(from photometry, Mignoli et al. ’04) – 6/8 sources 2/8 sources: secure spectroscopic redshifts from ISAAC (Maiolino et al. ’06) J H KS J H KS LINER (X/O=52) Maiolino et al. 2006 QSO 1.9 (X/O=78) NH~1023 cm-2 + L2-10 keV>1044 erg/s Type 2 QSOs

KS-band images with 24 μm contours 40 arcsec All sources detected in IRAC & MIPS24 S(24 μm)=150-1000 μJy

Spectral Energy Distribution: the modeling (I) Bulge-dominated sources Host galaxy Elliptical galaxy normalized to Ks + Torus emission Template from Silva et al. ’04 Lbol=f(LX; NH) every source model normalized using its X-ray luminosity and NH values Silva et al. 2004

Bulge-dominated sources (in KS): nuclear vs. host-galaxy emission • Elliptical galaxy • + • nuclear component • = • match the data within a factor of 2-3 • Nuclear comp. consistent with KS upper limits • Nucleus starts dominating at ≈6 μm from Pozzi et al., WORK IN PROGRESS NUCLEAR COMPONENT: not a SED fitting!  normalized to X-ray observables: LX and NH

Spectral Energy Distribution: the modeling (II) Point-like sources (in the KS band) Extincted Type 1 quasaror red quasar template (from Polletta et al. 2006) normalized to 24 μm • Extincted Type1 quasar NOT able to reproduce the data sharp decrease in the optical • Good match using a red QSOtemplate from Pozzi et al., WORK IN PROGRESS

1. Sum the radiation directly linked to the accretion  LBOL=LX,INT + LOPT,UV REQUIRED: ►to remove IR bump (re-processed radiation) ►to correct for gas/dust absorption in X-ray, optical, and UV 2.Integration of the observed luminosities  LBOL≈∫ observed SED = LX,OBS+ LIR,OBS LBOL Bolometric correction and luminosity Bolometric luminosity = LBOL = kX L2-10 keV bolometric correction (≈35 in Type 1 QSOs from Elvis+ 94) BUT large dispersion in the broad-line QSO SEDs our approach

Corrections applied to the obtained face values to account for • covering factor ↔ opening angle of the torus ↔ N(AGN2)/N(AGN1) in this LX range from Gilli+ 07 XRB models factor 1.5 • anisotropy ↔ only part of the re-emission from the torus reaches the observer  ≈10%according to Silva+ 2004 templates from Urry & Padovani 1995

Bolometric correction: preliminary results Median kX = LBOL/L2-10 keV ≈ 27 Red QSO at z=2.08 point-like bulge-dominated

Bulge and black hole masses Bulge-dominated sources KS-band flux mostly from the host galaxy  LK  MBH using the Marconi & Hunt (2003) local relation and assuming (MBH/M*)z=1 = 2(MBH/M*)z=0(Peng+ 06) <MBH> ≈ 109 M Eddington ratio=LBOL/LEDD ≈ 0.06

BH masses: comparison with SDSS quasars Indications that: • these luminous obscured QSOs, residing in KS-luminous galaxies, have massive black holes SDSS data from McLure & Dunlop ’04

Eddington ratios: comparison with SDSS QSOs Indications that: • these very massive, X-ray luminous black holes at z≈1-2 have alreadypassed their rapidly accreting phase • they have reached their final masses with low accretion rates SDSS data from McLure & Dunlop ’04

if you have questions… I’m not sure I can answer … THE END

Luminous obscured quasars in the HELLAS2XMM survey: the Spitzer perspective