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Abundances in the BLR

Abundances in the BLR. Nathan Stock February 19, 2007. Motivation. Metallicity affects properties of the AGN (Ferland, 1996) Opacity Kinematics Structure Outflows enrich IGM (Friaca, 1998) Dust increases obscuration of high-z objects. Motivation.

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Abundances in the BLR

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  1. Abundances in the BLR Nathan Stock February 19, 2007

  2. Motivation Metallicity affects properties of the AGN (Ferland, 1996) Opacity Kinematics Structure Outflows enrich IGM (Friaca, 1998) Dust increases obscuration of high-z objects

  3. Motivation Provides information on chemical history of the gas (Ferland 1996) Representative of much larger region (~100’s pc) than BLR itself (>1 pc) Constrain early nucleosynthesis / SFR in the host galaxy

  4. Typical QSO Spectra Hamann 1999

  5. Collisionally excited lines Line strengths of collisionally excited lines High density limit Low density limit Hamann 1999

  6. Recombination lines Especially relevant for H, He Line strength (oversimplification) Hamann 1999

  7. Calculating abundances Take the ratio of two lines Adjust from abundance of element in ionized state to total abundance Express in standard form Hamann 1999

  8. Typical QSO Spectra Hamann 1999

  9. But wait… • CIV acts as a cooling • line: as C/H ↑, • temperature ↓ CIV/Lyα ratio does not depend on metallicity Hamann 1999

  10. And there’s more… We want the lines to be emitted from the same region of the BLR i.e. elements have similar ionization energies Differing ne, β in different regions Different continua as well Hamann 1999

  11. And more… We want similar values of ncrit Removes possible dependence on ne Both emitters either in high density or low density limit Note: similar ncrit does not help if the emitters are in different regions of the BLR! Hamann 1999

  12. Problem 1: Appropriate element To find metallicity, we cannot use C/H when Z>.02 Zsun Moreover, C and other elements don’t have ions in the same range as HII Ratios of elements to each other would also seem counterproductive, but… Hamann 1999

  13. Secondary production of N C, N, O produced in later stages of stars N is also produced in CNO cycle Valid for Z>.2 Zsun Result: N/O α O/H α Z Hamann 1999

  14. Caveat: secondary N is delayed Delayed production will be important if Z enrichment is faster than stellar lifetimes This is true in dense environments So, q is a delay factor q=0 in slow evolution limit q~.5 in fastest evolutions Hamann 2001

  15. Problem 2: Appropriate ionization We want lines that are emitted from the same region of the BLR (co-spatial) Need to model ionization regions Define U, nH, abundance, incident spectrum Use CLOUDY to identify ionized regions Hamann 2001

  16. Results for a ‘typical’ BLR • nH = 10^10 • U = .1 • Solar abundances Hamann 2001

  17. Problem 3: Appropriate ncrit We want critical densities to be similar Ensures ions are in same density limit in each part of the BLR Hamann 2001

  18. Putting it together We can model how emission line intensities (equivalent widths) vary… …with the flux of incident ionizing photons (ΦH) … with hydrogen density (nH) Integrating the intensities over (ΦH, nH) space (with appropriate weighting) gives us the total line strength Hamann 2001

  19. Example: CIII] λ977 ΦHtoo low, C is neutral ΦHtoo high, C is ionized In both limits, the CIII] equivalent width is weak nH too high, exceed ncrit Emission line is collisionally suppressed nH too low, forbidden lines become efficient coolants Gas temperature drops, weakening emission lines Hamann 2001

  20. Equivalent Widths of lines Hamann 2001

  21. Flux Ratios of lines Hamann 2001

  22. Total line strength Integrate over the space to find the line strength 714 for log nH 1724 for log ΦH Assume equal weighting Previously shown to reproduce AGN broad emission lines fairly accurately (Baldwin 1997) Similarly, we can find the total line ratio Hamann 2001

  23. Finding line ratio – Z relations Previously considered solar abundance Now, vary the abundances Recalculate emission line ratios Hamann 2001

  24. Dependence affected by shape of incident spectrum • Solid curve: MF87 spectrum • Dotted curve: α=-1 power law • Dashed curve: segmented power law Hamann 2001

  25. NIII]/OIII] and • NV/HeII: • N found in narrower region  line ratios will underestimate abundances Things to note: Hamann 2001

  26. Possible NV contamination? NV NV line at λ1240, Lyα at λ1216 If NV is moving away from Lyα at the right velocity, it can absorb and rescatter Lyα emission v ~ 5900 km/s  achievable in BAL winds Lyα Hamann 1999

  27. BAL contributions likely small Only ~30% of Lyα photons interact with NV in BAL Most Lyα passes through Given 12% BAL covering factor & typical BAL velocity profile NV BAL < 25% NV BLR Moreover, BAL peak would be much wider >10,000 km/s BAL vs. 2500 km/s BLR half-widths Do not see this in spectra Hamann 1996

  28. Line ratios taken from the literature on quasars imply they have BLR regions which have greater than solar metallicities. Integ Hamann 2001

  29. Abundances in Quasars All the most robust line ratios show Z~2-3Zsolar is typical all quasars Abundances constitute a lower limit on actual Z because we assumed q=0 In quasars, q is almost certainly not 0! Hamann 2001

  30. More quasar data 70 quasars, each Z found by averaging several N ratios Average metallicty of the sample: Z~4 Zsolar Dietrich, 2003

  31. What does this high Z tell us? High metallicity  significant chemical evolution occurred before our observations Even at the highest redshift quasars! Chemical evolution models imply most of the original gas has been processed by stars Vigorous star formation and evolution likely precedes the epoch of quasar activity Have ~1-2 Gyr of stellar formation time at z=5 Hamann 2001

  32. Metallicity-Luminosity Relation? Metallicity-tracking line ratios in the BLR do not appear to correlate with redshift However, it DOES appear to correlate with quasar luminosity Nagao 2006

  33. Metallicity-Luminosity Relation? Is this relation fundamental or apparent? Evidence that it’s MBH that really matters Warner 2007

  34. Metallicity-MBH Relation What brings about this relation? MBHα Mhost (at least in local universe) We expect a more massive host galaxy to have a higher metallicity More stars producing elements Evidence that MBHα Mhost relation applies at high redshift as well A possible way to find host masses even at high redshift? Hamann 2007

  35. So what’s next? Direct measurements of host galaxies Mass, age, metallicity More samples, over a variety of properties Higher redshifts, lower luminosities The usual pushing the limits of what we can observe Other abundances Not just C, N, O Fe, Si? Hamann 2007

  36. Bibliography Dietrich, M., Hamann, F., et al. 2003, 589, 722 Ferland, G.J., Baldwin, J.A., Korista, K.T., et al. 1996, ApJ, 461, 683 Hamann, F., Dietrich, F. & Ferland, G.J. astro-ph 0701503 Hamann, F., & Ferland, G.J. 1999, ARA&A, 37, 487 Hamann, F., & Korista, K.T. 1996, ApJ, 464, 158 Hamann, F., Korista, K.T., Ferland, G.J., et al. Astro-ph 0109006 Nagao, T., Marconi, A., & Maiolino, R. 2006, A&A, 447, 863 Sadat, R., Guiderdoni, B. Silk, J. 2001,°a, 369, 26 Warner, C., Hamann, F., & Dietrich, M. 2007, ApJ, submitted

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