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, Torino 2008 Outline • What are EXOs? • Sample selection • Multiwavelength properties • Optical identifications • Summary and conclusions • Future works Agnese Del Moro, Torino 2008 EXOs Dominant AGN population have X-ray to optical flux ratio Fx/Fopt ~ 1 EXOs are objects with extreme X-ray to optical ratio (and no optical r band detection, Koekemoer et al. 2004): Fx/Fopt > 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. 2007) Agnese Del Moro, Torino 2008 Our sample • 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 - Fx ≥ 10-13 erg cm-2sec-1 (0.2-12 keV) - Fx/Fopt> 30 Fx/Fopt> 10 in the 2-10 keV band Agnese Del Moro, Torino 2008 Advantages of our approach: • X-ray fluxes 10-1000 times brighter than samples based on deep surveys • Large sky area • Good X-ray data Γ and NH • Optical/NIR analysis is possible at these fluxes Mignoli et al.2004 THE FINAL SAMPLE: 130 sources (~10% of the AGN) 16 “known” objects 114 new objects ~30% of them have no detection in SDSS Agnese Del Moro, Torino 2008 Hardness Ratios HR= (H-S)/(H+S) HR2: S=0.5-1 keV H=1-2 keV HR3: S=1-2 keV Known Objects H=2-4.5 keV New Objects Agnese Del Moro, Torino 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 by ≤30% Agnese Del Moro, Torino 2008 EROs 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, Torino 2008 Type 2 QSOs 2XMMp J0922 From optical spectrum: NL AGN z = 0.57 Γ = 1.54 NH = 3.2 x 1022 Lum (2-10 keV) ≈ 3 x 1044 erg/sec (unabsorbed) 2XMMp J1253 From optical: NL AGN z = 0.94 Γ = 1.52 NH = 2.2 x 1022 Lum (2-10 keV) = 3.4 x 1044 erg/sec (unabsorbed) Agnese Del Moro, Torino 2008 Summary and Conclusions 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 Agnese Del Moro, Torino 2008 Ongoing and future… • 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, Torino 2008