seeking type 2 qso amongst bright x-ray selected exos

Seeking type 2 QSO amongst bright X-ray

selected EXOsAgnese 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


• What are EXOs?

• Sample selection

• Multiwavelength properties

• Optical identifications

• Summary

• Future works


EXOsDominant AGN population have X-ray to optical flux ratio Fx/Fopt ~ 1EXOs 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)


• 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

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

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


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


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


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


OUR SAMPLE

X/O=10

Type 2 QSOs


2XMMp J0922

From optical spectrum: NL AGN

z = 0.57Γ = 1.54NH = 3.2 x 1022

Lum (2-10 keV) ≈ 3 x 1044 erg/sec (unabsorbed)

2XMMp J1253

From optical: NL AGN

z = 0.94Γ = 1.52NH = 2.2 x 1022

Lum (2-10 keV) = 3.4 x 1044 erg/sec (unabsorbed)

Summary


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…


• 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

seeking type 2 qso amongst bright x-ray selected exos

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