Seeking type 2 QSO amongst bright X-ray selected EXOs Agnese Del Moro University of Leicester, UK In collaboration with: M.G. Watson (UoL), S. Mateos (UoL), M.Akiyama (University of Tohoku, Japan) Agnese Del Moro, Granada 2008

Outline Agnese Del Moro, Granada 2008 What are EXOs? Sample selection Multiwavelength properties Optical identifications Summary Future works

Agnese Del Moro, Granada 2008 EXOs Dominant AGN population have X-ray to optical flux ratio F x /F opt ~ 1 EXOs are objects with extreme X-ray to optical ratio (and no optical r band detection, Koekemoer et al ):  F x /F opt > 10 What can they be? - rare galactic objects (INS, X-Ray Binaries, CV, ULX…) - highly variable objects - BL Lacs - high-z clusters - high-z AGN - highly obscured AGN Why are they important?  Constrain the fraction of EXOs powered by AGN  A large population of type 2 AGN is required by synthesis models of the X-ray Background (CXRB, Comastri et al.1995; Gilli et al )

Agnese Del Moro, Granada 2008 Cross-match with 2XMMp and SDSS DR5 catalogues: - Joint area ~75 sq.deg. - ~20,000 secure matches based on Likelihood Ratio analysis (Sutherland and Saunders 1992) SELECTION CRITERIA: - X-ray point sources - F x ≥ erg cm -2 sec -1 ( keV) - F x /F opt > 30  F x /F opt > 10 in the 2-10 keV band Our sample

Agnese Del Moro, Granada 2008 Advantages of our approach: X-ray fluxes times brighter than samples based on deep surveys Large sky area Good X-ray data  Γ and N H Optical/NIR analysis is possible at these fluxes THE FINAL SAMPLE:  130 sources (~10% of the AGN)  16 “known” objects  114 new objects  ~30% of them have no detection in SDSS (r’>22.5 mag) Mignoli et al.2004 OUR SAMPLE

Agnese Del Moro, Granada 2008 Hardness Ratios HR= (H-S)/(H+S) HR2: S=0.5-1 keV H=1-2 keV HR3: S=1-2 keV H=2-4.5 keV Known Objects New Objects

Agnese Del Moro, Granada 2008 Near-IR properties UKIRT UFTI and WFCAM data have been obtained for ~35% of the sample Optical/NIR colour analysis: - Our sources have typically red colours - 3 of them have r–K > 5 typical of EROs - the fraction of EROs is a lower limit; it may increase to ~30% EROs

Agnese Del Moro, Granada 2008 Optical identifications Optical spectra have been obtained with Subaru FOCAS for 16 of our EXOs From preliminary spectral analysis: 10 Broad Line AGN 5 Narrow Line AGN 1 Not identified Redshifts 0.4 < z < 1.6  Luminosities typical of QSOs  Unexpected large fraction of type 1 AGN  5 new type 2 QSO candidates

Agnese Del Moro, Granada 2008 OUR SAMPLE X/O=10

Type 2 QSOs Agnese Del Moro, Granada XMMp J0922 From optical spectrum: NL AGN z = 0.57 Γ = 1.54 N H = 3.2 x Lum (2-10 keV) ≈ 3 x erg/sec (unabsorbed) 2XMMp J1253 From optical: NL AGN z = 0.94 Γ = 1.52 N H = 2.2 x Lum (2-10 keV) = 3.4 x erg/sec (unabsorbed)

Summary Agnese Del Moro, Granada 2008 We selected a sample of high X-ray-to-optical ratio X-ray bright sources from the cross-match between 2XMMp and SDSS DR5 catalogues * We have obtained one of the largest X-ray selected EXO sample * Evidence of absorption from X-ray HR2 colour for > 33% objects * Typical red optical/NIR colours, reaching also values typical for EROs for up to ~30% of the analysed sub-sample * Discovery of 5 new type 2 QSO candidate from optical spectra  2 “genuine” TYPE 2 QSOs * Unexpected large population of type 1 QSOs

Ongoing and future… Agnese Del Moro, Granada 2008 New optical spectra coming soon from VLT-FORS2  extend our analysis and increase the sample of identified objects. Detailed X-ray spectral analysis to constrain X-ray absorption Detailed optical spectral analysis to investigate properties of lines and optical reddening Further investigations on the type 1 population amongst our sample Development of an SED model in order to study the global properties of the sample and to investigate the AGN-host galaxy contributions

Agnese Del Moro, Granada 2008 Simple model of a typical QSO from the optical to the IR:  QSO SED + galaxy SED (Polletta et al. 2006)  galactic absorption (Pei 1992)  intrinsic absorption Assumptions:  Galaxy fraction (5% of the tot)  Dust-to-gas ratio (MW value) * Optical colours evolution with redshift * F x /F opt evolution with redshift IRAC1 IRAC2 The Model