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Revealing X-ray obscured Quasars in SWIRE sources with extreme MIR/O

Revealing X-ray obscured Quasars in SWIRE sources with extreme MIR/O. Giorgio Lanzuisi Fabrizio Fiore Enrico Piconcelli Chiara Feruglio Cristian Vignali. Accretion History of the Universe: Open Issues.  The resolved fraction of the CXB at > 8 keV is only 50%.

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Revealing X-ray obscured Quasars in SWIRE sources with extreme MIR/O

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  1. Revealing X-ray obscured Quasars in SWIRE sources with extreme MIR/O Giorgio Lanzuisi Fabrizio Fiore Enrico Piconcelli Chiara Feruglio CristianVignali

  2. Accretion History of the Universe: Open Issues •  The resolved fraction of the CXB at > 8 keV is only 50%. • Synthesis models require a population of heavily obscured AGN • A “factor 2” SMBH relics wrt expectations based on Hard X-ray LF •  In the local universe ~ 50% of Seyfert 2 are CT • But Few Compton-thick AGNs detected (Tozzi+06, Akylas+06, Alexander+08) • The LF of highly obscured AGN is still unknown • particularly at high luminosity • Relevant consequences for cosmology: • Tight link between SMBH mass density, nuclear activity and galaxy formation and evolution La Franca et al. 2005

  3. Searching for Obscured AGN: Mid-IR selection The MIR band is promising since absorbed opt/UV/X-ray AGN light is thermally 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 ~ to optically-bright QSO population Fiore+08: Extreme Sources with MIR/O>1000 and R-K>4.5 in the CDF-S Found a “factor 2” population of CT AGN candidates at Lx ~ 1043 (deep pencil-beam survey: HST+VLT+Spitzer+Chandra data on the CDFS; e.g. Daddi+07 for a similar result) Stacked image of undetected sources A complementary study is needed to investigate the high luminosity part of the LF of obscured AGNs

  4. The XSWIRE survey: a unique opportunity Given the low surface density of luminous QSOs, the sampling of a large area is required The Spitzer Wide-Area Infrared Extragalactic Survey covers with medium-deep MIPS and IRAC photometry ~50 deg2 of the sky. We have collected all available Spitzer and Optical photometric data on 5 SWIRE fields (http://www.oa-roma.inaf.it/~fiore/XSWIRE) 43 deg2 The X-ray coverage of the SWIRE fields is incomplete and highly inhomogeneous with exposure times ranging from 5 ks Chandra to 70 ks XMM-Newton observations (6.5 deg2) Elais-N1 Elais-S1 Elais-N2 Goal: Confirmation of the obscured AGN nature of the MIR-selected sources using the X-ray spectral analysis LockmanHole XMM-LSS

  5. Sample Selection X-ray Coverage, MIR/O>2000 and F(24m)>1.3mJy Flux limit chosen to have a sample of 44 sources All but one source fall in the AGN region of the IRAC color-color diagram, and most of them show extreme colors (i.e. log(F5.8/F3.6) > 0.4 and log(F8.0/F4.5) > 0.4) Polletta+08 Obscured QSO

  6. IR properties of the sample Our selection criterium MIR/O>2000 is well suited to find high IR luminous sources The large area of SWIRE allows to collect sources with LIR by a factor 5 higher of C-COSMOS (2 deg2) sources and factor 15-20 higher of CDF-S (<0.1 deg2) sources C-COSMOS Fiore+08b CDF-S Fiore+08a LMIR can be used as a proxy for L2-10 keV: LMIRαLbolα LX (Steffen+06; Polletta+08; Piconcelli+07)

  7. The sample Our sample consists of 44 eXtreme MIR/O flux ratios Galaxies (XMOGs) • X-ray • 25/44 have a positive X-ray • detection in the 0.5-10 keV band • For 23 is possible to • calculate the NH from: • HR (11 sources) • Spectral analysis (12 sources) • Redshifts • 7 Spectroscopic: • All but one(z=0.22) are • 0.7≤ zsp≤2.5 • 37 Photometric: • 19/44 from SWIRE Photometric Redshift Catalogue • (Rowan-Robinson+08) • For the remaining 18 XMOGs we calculated a zphot using the Fontana+00 method (e.g. also Feruglio+08) • 0.54≤zphot≤3.77

  8. Results: NHvs LumX Source Breakdown: . Obscured (NH>1022) 55-95% Unobscured 5-45% QSO 2s 40-55% 18% of the detected sample are promising C-thick QSO 2s candidates Control Sample (randomly selected): Obscured (NH>1022) 20% Unobscured 80% QSO 2s 5% Lanzuisi et al. 2008 We check the reliability of the HR technique in case of very low spectral counts The source falling out of the 1:1 relationship is the CT candidate  the HR underestimate the NH for CT sources?

  9. Results: X/O ratio • 20% of hard x-ray selected sources show extreme FX/FO ratios (i.e. X/O > 10) • Most of EXOs are obscured AGN at z > 1 • Nuclear optical light is blocked, differently from X-ray • Fiore+03 found that: • X/O is a proxy of obscuration •  correlation between X/O and LX XMM-LSS Garcet+07 Sources with X/O > 10 have NH>1022

  10. X-ray Spectra NH >1.4x1024 L2-10 > 1.4x1045 zphot~1.44 NH > 3x1023 L2-10 > 1.7x1044 zspec= 2.54 NH > 2.8x1023 L2-10 > 1.3x1044 zspec= 2.31

  11. Future Perspectives • We demonstrate the efficiency of our MIR/O selection over a large area survey • to find out a large fraction of QSO2. • OPEN ISSUES: • A fraction of sources is undetected even in medium/deep exposures (possibly CT?) • Deep Chandra/XMM exposures of the most interesting sources • (Next AO XMM-Newton, Chandra) • A complete X-ray survey of high MIR/O, high F24 sources is still lacking due to the highly inhomogeneous X-ray coverage • Chandra AO10 LP proposal submitted (PI. Fiore) to observe with deep (35-60 ks) exposures the 10 most extreme (MIR/O>2000 F24> 4 mJy) SWIRE sources with zspec • By joining this sample to the CDFS and • C-COSMOS samples we will able to • determine the “bolometric” LF of both • unobscured and highly obscured AGNs • in several redshift bins.

  12. Summary We selected a sample of 44 SWIRE sources with extreme MIR/O flux ratios (MIR/O>2000) and F24m >1.3 mJy • Spectroscopic and Photometric redshifts are 0.7 < z < 3.7 • We are able to infer the X-ray spectral properties for 23/44 XMOGs  Most (50-95%) are Obscured or Highly Obscured  ~50% are QSO 2s  ~20% are promising C-thick QSO 2s candidates Lanzuisi et al. 2008 We tested that our MIR selection applied to a large area survey like SWIRE is very efficient in collecting a large number of heavily obscured QSO2s More detailed X-ray and optical follow-up studies have been planned…

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