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General Assembly of IAU, Symposium #238 Black Holes: From Stars to Galaxies

X-ray Spectral Evolution of AGN. Presented by: George Chartas (Penn State) In collaboration with: Cristian Saez(Penn State), Xinyu Dai(OSU), Michael Eracleous(Penn State), Niel Brandt(Penn State), Bret Lehmer(Penn State), Franz Bauer(Columbia) , Gordon Garmire (Penn State).

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General Assembly of IAU, Symposium #238 Black Holes: From Stars to Galaxies

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  1. X-ray Spectral Evolution of AGN Presented by: George Chartas (Penn State) In collaboration with: Cristian Saez(Penn State), Xinyu Dai(OSU), Michael Eracleous(Penn State), Niel Brandt(Penn State), Bret Lehmer(Penn State), Franz Bauer(Columbia), Gordon Garmire (Penn State) General Assembly of IAU, Symposium #238 Black Holes: From Stars to Galaxies Aug 22, 2006, Prague, Czech Republic

  2. Evolution of AGN • Commonly used methods of studying the evolution of AGN include : • (a) Determining the evolution of the optical and X-ray luminosity functions and optical and X-ray space densities of AGN. • (b) Determining the evolution of the host galaxies. • (c) Determining the evolution of the spectra of the AGN ( vs z,ox vs z).

  3. Evolution of Space Density of type-I AGN The space density of type-I AGN changes significantly with redshift and luminosity. The redshift at which the space density peaks changes with luminosity from z ~ 0.5-0.7 for logLx = 42-43 ergs s-1 to z ~ 2 for logLx = 45-46 ergs s-1. The amount of change in the space density is also strongly dependent on luminosity.  ~ 10 for logLx = 42-43 ergs s-1  ~ 100 for logLx = 45-46 ergs s-1 The space density of low luminosity AGN is found to decline at high redshift. Hasinger et al (2005)

  4. Evolution of Host Galaxy Barger et al. 2005 The absolute rest-frame 5000 A luminosities of the host galaxies vs. redshift for sources in the ACS GOODS-North region of the CDF-N. Triangles : LX > 1044 ergs s-1 Diamonds: LX = 1043 - 1044 ergs s-1 Squares: LX = 1042 - 1043 ergs s-1

  5. Evolution of Quasars • One might expect to detect a change in the X-ray emission and accretion properties of quasars to accompany the dramatic change in the number density of quasars between z=1 and z=2 (Fan et al. 2001). • Many X-ray surveys have attempted to find such a change by constraining G and the optical-to-X-ray spectral index, aox • The evolution of G with z is still debatable (eg., Bechtold et al. 2003, Vignali et al. 2003, Grupe et al. 2005) • There is no indication that G correlates with luminosity for low z quasars (George et al. 2000, Reeves & Turner 2000) Evolution of quasar comoving number density as a function of z (Fan et al. 2001)

  6. Dependence of aox of AGN with UV luminosity and z Correlationof ox with z,only 1 sigma significantif the lUV dependenceis taken into account. Strateva et al. (2005) ox dependence on the2500 A monochromatic luminosity. The main sample isgiven by filled circles,the high-z sample byopen squares, and theSy 1 sample byopen Triangles. Strateva et al. (2005)

  7. X-ray Spectra of Radio-Quiet Quasars at z > 4 χ2 contours from joint fit for entire and common energy ranges • Shemmer et al. (2005) performed an investigation of moderate-to-high quality X-ray spectra of 10 quasars (z = 4 - 6.28). • They do not find any significant difference between the spectra of these high z quasars compared to ones at lower z. • If quasars have been evolving constantly over time observations of the most distant ones may provided the most ``leverage'' for constraining any changes in the X-ray spectra over cosmic time. • = 1.97 +/- 0.05, NH < 3 X 1021 cm-2 (mean values) Fe Kα EW < 190 eV and R < 1.2

  8. X-ray Spectra of Radio-Quiet Quasars at z > 4 Shemmer et al. (2005) find significant scatter of  but no systematic trend of  with absolute B magnitude and redshift. |d/dz| < 0.04

  9. Gravitational lensing as a tool to study AGN evolution • Employing the lensing magnification effect to observe high redshift quasars allows us to probe the luminosity range of 1043-45 ergs s-1. (This luminosity range is practically inaccessible by most Chandra observations of unlensed quasars of similarly high redshift.) • The lensing magnification (from a few to ~ 100) allows us to obtain moderate to high S/N spectra • The main scientific goal of our survey of quasars was to study the evolution of spectroscopic properties of high redshift RQQs by searching for a possible correlation between photon index G and luminosity for high redshift quasars

  10. Evolution of Radio Quiet AGN • - LX diagram from our recent analyses of high redshift (z > 1.5) radio quiet AGN. Significant correlations are found between G and the 0.2-2keV (2-10keV) luminosities. The correlations are significant at the 99.9997% (98.6%) confidence levels, respectively. (Dai, Chartas, Eracleous & Garmire 2004)

  11. Evolution of Radio Quiet Quasars • Photon index vs. 2-10 keV luminosity for low redshift (z < 0.1 mostly) AGN. No significant correlation is found (George et al. 2000)

  12. Evolution of Radio Quiet AGN • To confirm the previously observed correlation between  and luminosity we have: • Observed additional high z lensed AGN as part of the Chandra GTO program • Have analyzed moderate-to-high redshift radio quiet AGN observed in the deep field observations performed with Chandra • The larger sample allowed us to: • Place tighter constraints on the correlation • Test the correlation in narrower redshift bands and thus better constrain the epochs at which possible changes in the average emission properties of AGN occurred.

  13. Evolution of Radio Quiet AGN Recent lensed high redshift AGN observed with Chandra and added to our sample Object zs ms Exposure (ks) 15 20 15 20 20 Q 0142-100 BRI 0952-0115 Q 1017-207 SBS 1520+530 SDSS 0903+5028 2.72 4.50 2.55 1.59 3.605 I=16.47 I=18.3 I=16.78 I=17.61 R=19.56

  14. Evolution of Radio Quiet AGN

  15. Using Chandra Deep Field Observations to Study AGN Evolution

  16. Using Chandra Deep Field Observations to Study AGN Evolution 1000.0 CDF - N CDF - S CDF - N, z > 1.5 CDF - S, z > 1.5 100.0 Number of Sources > N Counts 10.0 1.0 0 500 1000 1500 2000 N Counts

  17. Using Chandra Deep Field Observations to Study AGN Evolution Source Selection • Selected the radio-quiet AGN from the CDF surveys with Nph (0.5-8 keV) > 200 cnts (~130 sources with z > 0.5) • Radio loud objects were filtered out using R = f5GHz/f4400A> 10 Afonso et al. (2006), Richards (2000) (~22/152 RLQs, ~14%). Spectral Analysis • 200 < Nph < 600 Cash statistic • Nph > 600 2 statistic • Model : Absorbed power-law • Fitting range: (a) 0.5-7keV observed frame (b) 2-10keV rest frame

  18. Using Chandra Deep Field Observations to Study AGN Evolution

  19. Using Chandra Deep Field Observations to Study AGN Evolution

  20. Using Chandra Deep Field Observations to Study AGN Evolution <> = 1.64 +/- 0.34 <> ~ 2.6 x 1022 cm-2 Histograms of  and NH

  21. Using Chandra Deep Field Observations to Study AGN Evolution Correlation Results:  - L(2-10 keV) & 1.6 < z < 3.3 Spearman: rc = 0.57 P(r > rc) = 7.1 x 10-4 Pearson: r = 0.55 P(r > rc) = 1.1 x 10-3  - L(2-5 keV) & 1.6 < z < 3.3 Spearman: rc = 0.59 P(r > rc) = 4.3 x 10-4 Pearson: re = 0.61 P(r > re) = 2.3 x 10-4 All spectral fits performed in the 0.5-7 keV observed frame

  22. Using Chandra Deep Field Observations to Study AGN Evolution Correlation Results:  - L(2-10 keV) & 1.6 < z < 3.3 Spearman: rc = 0.43 P(r > rc) = 2.4 x 10-2 Pearson: rc = 0.49 P(r > rc) = 7.6 x 10-3  - L(2-5 keV) & 1.6 < z < 3.3 Spearman: rc = 0.54 P(r > rc) = 2.9 x 10-3 Pearson: rc = 0.61 P(r > rc) = 5.8 x 10-4 All spectral fits performed in the 2-10 keV rest-frame

  23. Using Chandra Deep Field Observations to Study AGN Evolution

  24. Using Chandra Deep Field Observations to Study AGN Evolution Correlation Results:  - L(2-10 keV) & 1.6 < z < 3.3 Spearman (1e43 - 5e45erg/s): rc = 0.6 P(r > rc) = 5 x 10-7 Pearson (1e43 - 2e45erg/s): rc = 0.51 P(r > rc) = 1.4 x 10-4

  25. Using Chandra Deep Field Observations to Study AGN Evolution Possible Interpretations of the LX -  Correlation • First Interpretation • Narrow range of M at high z • Large range of accretion rate • Second Interpretation • Narrow range of accretion rate at high z • Large range in M

  26. Using Chandra Deep Field Observations to Study Quasar Evolution • Physical Interpretations of LX -  • Hot corona model by Haardt et al. 1997 • predicts that  increases with  of the corona  decreases with T of the corona • If the corona is dominated by • electron-positron pairs this model also • predicts that •  Log Lx

  27. Conclusions • We confirm the Lx -  correlation for radio quiet AGN at high z based on the spectral analysis of the CDF surveys. • We find that the strength of Lx -  correlation is z dependent and peaks at z ~ 2.2 • The Hot Corona model predicts the Lx -  correlation • The redshift dependence of the correlation suggests that quasars near the peak of their comoving number density are accreting near Eddington and have different accretion properties than their low-z counterparts

  28. Evolution of Radio Quiet Quasars Under the assumptions: that high-z quasars emit near Eddington that the optical depth t of the corona is dominated by electron-positron pairs. The observed range in luminosity is due to a range in BH masses (~ 2-3 orders of magnitude) the hot corona model of Haardt & Maraschi 1993 predicts : G log[L(2-10keV)] The redshift dependence of the correlation implies that quasars near the peak of their comoving number density are accreting near Eddington and have different accretion properties than their low-z counterparts Possible Interpretation of G-Lx is based on the hot corona model (Haardt & Maraschi 1993, Haardt, Maraschi, & Ghisellini 1997)

  29. Conclusions The spectral slope of the 1.4 < z < 4 radio-loud quasars appears not to vary significantly over 4 orders of magnitude in 2-10 keV luminosity. We do not find a significant correlation between the spectral slope G and X-ray luminosity as found in our 1.5 < z < 4 radio-quiet quasar sample. The spectral slopes of the radio-loud quasars of the sample are significantly flatter than those of the radio-quiet sample possibly due to contamination from jet emission. The limited number of quasars in the present sample combined with the medium S/N of several of the observations may have led to an unaccounted for systematic effect. Additional observations of z ~ 2 lensed radio-loud quasars with better S/N will allow us to obtain tighter constraints on a possible correlation between G and X-ray luminosity. (d) The X-ray variability of the high redshifts radio-loud quasars of our sample is consistent with the known correlation between excess variance and luminosity observed in NLS1s when extrapolated to the larger luminosities of the present sample.

  30. CREDITSDirectorGeorge ChartasActorsXinyu DaiMichael EracleousDigital Camera PersonnelGordon Garmire

  31. Model Predictions • Haardt, Maraschi, & Ghisellini (1997) predicted: • increases with , the optical depth of the Compton scattering. • decreases with T, the temperature of the corona.   Optical Depth of IC Scattering Temperature of Corona

  32. In a “Compact” Corona • Haardt, Maraschi, & Ghisellini (1997) also predicted: • In COMPACT CORONA, where the pair production dominates,  Log Lx • This is similar to what we have observed.

  33. First Interpretation • Narrow range (of order a few) of M at high redshift. • Large range of . Two Possible Interpretations of the Correlation

  34. Second Interpretation • Opposite. The range is narrow, close to Eddington limits, and M range is large. • The lc is the “compactness” of the corona. • Haardt & Maraschi (1993) predicted that M  lc,  increases as lc increases. • Consistent with semianlyti-cal model of Hauffmann & Haehnelt (2000) for the cosmological evolution of super massive black hole and their fueling rates.  lc (Coronal Compactness)

  35. Evolution of Radio Quiet Quasars • We recently presented results from a survey of relatively high redshift (1.5<z<4) • gravitationally lensed radio-quiet quasars (RQQs) observed with the Chandra and XMM-Newton (Dai et al. 2004).

  36. Evolution of Quasars • Using gravitational lensing as a tool to study the evolution of distant quasars • Gravitationally Lensed High-z Radio Quiet Quasars • Near Eddington Luminosites at redshifts above z~1.5 • High-z Radio Quiet Quasars from the Chandra Deep Field Surveys • Conclusions

  37. Gravitational lensing as a tool to study AGN evolution Conceptual diagram of the gravitational deflection of light in a quad GL system.

  38. Understanding the Evolution of Quasars Soft photons IC scattering Black Hole Corona Accretion Disc Corona

  39. Using Chandra Deep Field Observations to Study AGN Evolution Histograms of Lx and z

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