Seeking type 2 QSO amongst bright X-ray selected EXOs

1. 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

2. Outline • What are EXOs? • Sample selection • Multiwavelength properties • Optical identifications • Summary and conclusions • Future works Agnese Del Moro, Torino 2008

3. 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

4. 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

5. OUR SAMPLE 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

6. 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, Torino 2008

7. EROs Near-IR properties UKIRT UFTI and WFCAMdata 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

8. 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

9. 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

10. 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

11. 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