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Núcleos galácticos activos

Núcleos galácticos activos

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Núcleos galácticos activos

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  1. Núcleos galácticos activos Gustavo E. Romero IAR (CONICET) Facultad de Ciencias Astronómicas y Geofísicas (UNLP)

  2. Radio source 3C273: Optical counterpart: faint (V=13 mag) star-like object, with strong “unidentified” emission lines “QUASAR” Quasi Stellar Source (QSS)

  3. In 1963 Maarten Schmidt identifies highly redshifted Balmer lines in 3C273’s spectrum z = 0.158 (vr = 47500 km/s)

  4. Radio “quiet” quasars were afterwards discovered (in fact, ~90% of all quasars are radio quiet) Quasi Stellar Objects (QSO) Today, the name quasar is used for objects in both classes, either radio loud (RLQ)or radio quiet (RQQ). • Main characteristics of QSOs: • High redshift high luminosity (-29.5 < MB< -21.5) • Strong, often broad, emission lines (not “HII region”) • Continuum and emission line variability • Broad spectral energy distribution (SED) from radio to -rays

  5. Seyfert galaxies Galaxies (mostly spirals) hosting an active nucleus

  6. Galaxies (mostly ellipticals) hosting an active nucleus, and strong radio emission, usually with a core + jet + lobes morphology Radio galaxies

  7. RQQ Seyfert galaxies radio galaxies luminosity radio power RLQ & blazars Active Galactic Nuclei (AGN)

  8. Optical spectra of different AGN types

  9. Spectral energy distribution (SED) High throughput over a broad frequency range

  10. thermal(disk) Synchrotron(jet) inverse Compton(jet) Spectrum of a gamma-ray blazar Lichti et al. (1994)

  11. AGN variability

  12. What is the engine of AGNs? • Fast variability small size Δx < c ·Δt • High energy output large mass • L ≤ LE = (4πG c mp M) / σe Up to several 1013Lo are generated within a few pc3 Nuclear fusion is insufficient Conversion of gravitational energy is more efficient Super Massive Black Hole (SMBH): M109Mo

  13. SMBH model & unification • blazar • Sy 1 • BLRG • QSO • Sy 2 • NLRG • IR QSO?

  14. AGN are complex objects • multiwavelength emitters • orientation effects (anisotropy) Behaviour is different along the spectrum • Hard X-rays are less affected by absortion • IR emission does not depend on orientation

  15. Central SMBHs are ubiquitous in bulge-dominated galaxies

  16. synchrotron thermal (dust) thermal (gas) inverse Compton RLQ (~10%) RQQ (~90%)

  17. Wilson & Colbert (1995, ApJ 438, 62) • RL AGN never occur in spiral hosts (and few RQ AGN in elliptical hosts) • Radio luminosity functions of Seyferts and radio galaxies are different • RL and RQ AGN have similar emission properties from IR to X ⇒ accretion is similar (Why) are there RL and RQ quasars? SMBH spin → RL AGN

  18. High spin SMBH from a merger

  19. NGC 6240: binary AGN in a recent merger Komosso et al. (2003, ApJ 582, L15)

  20. SMBH model & unification • blazar • Sy 1 • BLRG • QSO • Sy 2 • NLRG • IR QSO?

  21. Radio galaxy 3C 120(d = 140 Mpc) Superluminal motion: βA= βP sen(θ) / [1+βP cos(θ)]

  22. X-ray flux (RXTE) X-ray spectral index radio flux Marscher et al. (2002, Nature 417, 625)

  23. Generation of jets

  24. Optical microvariability observations: Powerfull tool to test the innermost components in AGNs Romero, Cellone, Combi, Andruchow, Araudo CASLEO 2.15-m “Jorge Sahade” Telescope • Photometry • 41 AGNs observed during ~65 nights • Polarimetry • ~15 objects • ~30 nights

  25. synchrotron inverse Compton A subset of RLQs with: blazars = Flat Spectrum Radio Quasars (FSRQ) + BL Lac objects (faint or absent emission lines) • “Flat” optical continuum • Rapid variability • Usually high and variable polarization • Superluminal motions

  26. Blazars: looking down the jet … • Relativistic effects are important • Doppler boosting:F = 4 F’ • (broadband flux) • = [ (1- cos)]-1Doppler factor • = v/c  = (1-2)-½Lorentz factor

  27. Blazars: looking down the jet … • Relativistic effects are important • Doppler boosting:F = 4x105 F’ • (broadband flux) • = [ (1- cos1o)]-1 = 13.9 Doppler factor • = v/c = 0.99  = (1-2)-½ = 7.1 Lorentz factor

  28. Ciprini et al. 2003, A&A 400, 487 Optical variability (B band) BL Lac object GC 0109+224

  29. Radio - Optical variability BL Lac object AO 0235+164 WEBT campaign (Raiteri et al.) Optical (R band) Radio (8 GHz)

  30. Jang & Miller (1995, ApJ 452, 582; 1997, AJ 114, 565) Romero, Cellone, Combi (1999, A&AS 135, 477) • Comparison of optical microvariability properties of different AGN samples • RLQ are more variable than RQQ • Microvariability due to propagating shocks in jets Miller et al. (1989, Nature 337, 627) Carini et al. (1990, AJ 100, 347; 1991, AJ 101, 1196; 1992, AJ 104, 15) • blazars display Δm ~ 0.05 mag in ~20 min • “Microvariability”

  31. Fan & Lin (2000, ApJ 537, 101) Gopal-Krishna et al. (2003, ApJ 586, L25) Sagar et al. (2004, MNRAS 348, 176) Stalin et al. (2004, MNRAS 350, 175) • Comparison of optical microvariability properties of different AGN samples • Among blazars, BL Lacs and HPQ are more variable (at short time-scales) • Microvariability correlates with polarization

  32. 1.2 mag (~3 times in flux units) brightening in ~24 hs AO 0235+164 (BL Lac object z = 0.94) 2.8 < C < 14.3 Romero, Cellone, Combi (2000, A&A 360, L47)

  33. Differential photometry: Atmospheric and/or instrumental fluctuations should thus be removed. AGN comparison and control stars ~20 images of each field per night  light-curve.

  34. mAGN – m*1 m*2 – m*1 (stability check) Differential light-curve: Variations larger than ~0.02 mag could be detected, on timescales of a few min Confidence level of variability: C = AGN/*2 C > 2.6  source is variable 1331+170 (FSRQ) C = 1.2 non-variable

  35. PKS 0537-441  BL Lac object (z = 0.894) Romero, Cellone, Combi (2000, AJ 120, 1192) Δm = 2.6 mag in 3 yr (ΔF > 10 x) 1998 2000 1997

  36. Origin of microvariability in blazars Intrinsic models: • Accretion disk instabilities (hot spots, etc.) • Shock-in-jet models • Geometric effects Extrinsic models: • Gravitational microlensing • Scintillation (radio only)