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The XMM-Newton/2df survey: a glimpse of the bright X-ray Universe

The XMM-Newton/2df survey: a glimpse of the bright X-ray Universe. I. Georgantopoulos NATIONAL OBSERVATORY OF ATHENS A. Georgakakis, O. Giannakis, S. Kitsionas, A. Akylas, D. Gaga, M. Plionis, V. Kolokotronis, S. Basilakos G.C. Stewart, M.G. Watson University of Leicester

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The XMM-Newton/2df survey: a glimpse of the bright X-ray Universe

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  1. The XMM-Newton/2df survey: a glimpse of the bright X-ray Universe I. GeorgantopoulosNATIONAL OBSERVATORY OF ATHENS A. Georgakakis, O. Giannakis, S. Kitsionas, A. Akylas, D. Gaga, M. Plionis, V. Kolokotronis, S. Basilakos G.C. Stewart, M.G. Watson University of Leicester E. Hatziminaoglou European Southern Observatory T. Shanks, M. Vallbe University of Durham B.J. Boyle AAO

  2. Overview XMM-Newton/2df survey NORTH 9 adjacent fields, 5-10 ksec exposure, ~2 deg2 200 sources in 0.5-8 keV in areas covered by both the 2-df and SDSS surveys The survey main goals are : a. Nature of various classes of AGN b. groups and poor clusters of galaxies (Basilakos et al. 2003 MNRAS submitted) c. Galaxies (Georgakakis et al. 2003 MNRAS astro-ph/)

  3. Motivation (why bother ?) • Explore the bright X-ray sky especially at hard energies • where the ASCA and BeppoSAX surveys lack spatial resolution • Bridge the gap between the Chandra surveys and bright fluxes • 2. Further explore the soft X-ray sky. • With a 10 ksec exposure we reach ~3x10-15 (0.5-2 keV) similar to the PSPC exposure in the LH (with better spatial positions and broad band spectra) • 3.Find BRIGHT NEARBY counterparts of the enigmatic sources detected • in the deep Chandra fields.

  4. Introduction ROSAT showed that the soft (0.5-2 keV) XRB is dominated by BL AGN In harder energies (2-10 keV) the logN-logS shows an excess of sources Relative to the ROSAT logN-logS (obscured AGN ?). Couldn’t tell Chandra surveys have shown that the X-ray background consists of various classes of sources: 1. QSOs 2. Obscured AGN 3. Optically ‘passive’ galaxies 4. Optically faint sources 5. Star-forming galaxies at very faint fluxes (Classes 3,4 may take into account the scarcity of obscured AGN) The nature of these new populations is hard to explore mainly due to the fact that these are quite faint

  5. Outstanding issues What is the nature of ‘passive’ X-ray galaxies (XBONG) ? Can the optically faint sources be obscured AGN at high z ? Where are the type-1.9/2 QSOs ? (only 3 detected in Chandra surveys) A number of Type-1 QSOs present large amounts of absorption ? The last two points present great interest for AGN unification models (and XRB population synthesis models)

  6. Survey Description 18 shallow 5-10 ksec pointings in the NGP/SGP covering ~4 deg2. WHY THERE ? Extended optical follow-up : Spectroscopic 2-df B<21 QSOs (NGP/SGP) Photometric B=22.5, spectroscopic by the SDSS (NGP) ADJACENT fields They can be observed in a single 2-df exposure to go fainter

  7. NGP details 0.5-8 keV 0.5-2 2-8keV --------------------------------------------- 215 197 61 (>6σ) 135 134 49 with optical c’parts p>98.5% 36 31 4 with opt. C’parts at p<98.5% 44 32 8 No opt. C’parts down to B=22.5 63 26 Spectroscopic Redshifts 2-df/SDSS/Deeper 2-df 23 4 Photometric Redshifts 2 sources in the 2-8 keV catalogue only13 sources in the soft 0.5-2 keV catalogue Hence the 0.5-8 keV total catalogue gives a fair representation of the X-ray populations What to remember: Spectroscopic Follow-up largely incomplete (possibly biased) Assigning probabilities helps to reject the chance coincidences

  8. logN-logS At these fluxes about 50% of the XRB is resolved in both bands Therefore our objects are typical of those making the XRB

  9. The fx/fo diagram Dominated by AGN (morphology suggests both nearby and distant AGN) Some galaxies are observed with low fx/fo 0.5-8 keV • Spectra: • X BL AGN •  NL/ABS Galaxy • Morphology: • Galaxy • Star • unclassified morph  Low prob.

  10. Optical Ids 2-df/SDSS and deeper AAT/2-df spectroscopy Vast majority in the 0.5-8 keV sample associated with broad-line AGN Type 0.5-8 2-8 --------------------------------- QSO/Sy1 54 21 NELG/Gal. 10 5 Star 5 2 No-ID 102 25

  11. Photometric Redshifts Using the Code of Hatziminaoglou et al. (1999) It does not work for extended objects where the colours are contaminated by the galaxy Object selection: 1. Stellar 2. High fx/fo 70% of these have Dz<0.3 (Kitsionas et al. 2003)

  12. The Redshift Distribution Excess number of sources at low Redshift (even when we take into account only the type-1) 0.5-8 keV Blue= type-2 Red= type-1 Green=Photom

  13. 2-8 keV

  14. The 0.5-2/2-8 hardness ratios Large columnns are observed, much higher than those encountered in type-1. Still these are lower than those predicted by population synthesis models. 0.5-8 keV 5 2-8 keV

  15. The column density histogram Surprisingly, the galaxies have A lower N_H than the point sources. Things get worse considering That the point sources are further Away and thus that the rest-frame N_H will be even larger 0.5-8 keV Two peaks with Galactic and moderate (logN_H~21.5) column densities

  16. 0.5-8 keV Spectra: X BL AGN  NL/Galaxy Morphology: Galaxy  Star Most galaxies are red but these are not necessarily hard ie there is not a simple picture where we find many Nearby Obscured AGN

  17. Where are the type 1.9-2 QSOs ? Only local type-2 AGN detected so far exception is RXJ at z=2.35 already discovered by ROSAT (Almaini et al. 1995, Georgantopoulos et al. 1999)

  18. 0.5-8 keV The 0.5-8 keV sample is dominated by the blue AGN. In the hard band red galaxies and blue AGN play equal roles 2-8 keV The colour-colour diagram easily picks out candidate type-2 AGN (Note that the HR of the red stellar objects is not hard)

  19. Type-1 QSOs with large N_H

  20. Correlation with redshift also found by Reeves & Turner 2000 (but logN_H~21 ) Corrected N_H for redshift Population synthesis models predict 2/3 logN_H>22 10-14 cgs 2-10 keV

  21. An Example at z=0.8 N_H= 3 (+-2)x10^21 cm-2 Photon index =1.9 fixed

  22. Implications for AGN unification models The apparent scarcity of type-2 AGN but mainly the observation of type-1 AGN with large amounts of X-ray absorption could possibly suggest that: At high redshifts Dust cannot survive but neutral gas can. Dust sublimates in the strong radiation field ? sublimation radius = 0.2 pc for L~1045 But then the X-ray absorbing gas must avoid ionization For 0.2 pc, L~1045 the ionization constant is relatively neutralξ =1 for densities n>109 cm-3 Dust coagulation is an alternative

  23. Optically passive galaxies Lx> 1043 for all 3 galaxies N_H=0 Photon index=1.9 fixed Cf Severgnini et al. in press

  24. Incompleteness of UVX surveys Not significant as far as the colour selection is concerned The optical extension may be a far bigger problem

  25. Summary Large number of sources at low redshift (even more pronounced at hard energies see Jahoda et al. 1991, Lahav et al. 1993) There is an apparent scarcity of absorbed (narrow-line) AGN at high redshift (same in IR wavelengths) Instead there is a number of type-1 QSOs with large column densities Type-1 AGN are many more than type-2 ? These have interesting implications for unification models. Dust sublimates but the gas remains neutral and hence absorbs X-rays ? No significant incompleteness of optical UVX surveys found due to colour selection.

  26. Galaxies • How we find them: • Objects with log(fx/fopt)<-1 • Extended in the optical • Additional criterion hardness • ratio • 2-4 galaxies in ALL 18 fields • Z=0.05-0.09

  27. Galaxies are quite rare: One would need tens Of XMM fields to form a decent sample

  28. Another way of determining the properties of galaxies is by using stacking analysis (>200 2df galaxies in our fields z~0.1)

  29. Extend at higher redshifts using radio galaxies Z~0.4

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