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What are Active Galaxies?

What are Active Galaxies?. Active galaxies have an energy source beyond what can be attributed to stars. The energy is believed to originate from accretion onto a supermassive blackhole .

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What are Active Galaxies?

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  1. What are Active Galaxies? Active galaxies have an energy source beyond what can be attributed to stars. The energy is believed to originate from accretion onto a supermassive blackhole. Active galaxies tend to have higher overall luminosities and very different spectra than “normal” galaxies. • Some classes of active galaxies: • Quasars • Seyfert galaxies (Type I and Type II) • Radio galaxies • LINERs “non-stellar” radiation stellar, blackbody radiation

  2. AGN radio loud classification: Radio galaxies: Giant E similar to radio quiet E with non thermal activity – origin: core (possibly X + optical) Extended: kpc scale FR I and FR II FR II BLRG and NLRG FR I only NLRG Compact: Low Power Compact CSS CSO GPS – nuclear only Intrinsic (young or frustrated) – geometry effects Radio power 1040 -- 1047 erg/s 1 erg = 0.1μJy 1 Jy = 10-26 W/Hz m2

  3. Radio galaxies of high and low power have quite different morphologies on the large scale (Fanaroff & Riley 1974) FR II : High power: P1.4 GHz > 1024.5 W Hz-1CLASSICAL DOUBLES EDGE BRIGHTNED : Radio core, asymmetric collimated jets, hot-spots Cyg A 3C 109 3C 219

  4. FR I : Low power: P1.4 GHz < 1024.5 W Hz-1 EDGE DARKENED : Radio core, symmetric jets with opening angles  10-15o, low brightness lobe 3C 296 3C 449 3C 31

  5. Quasars • First discovered in the 1960s. • Detected radio sources with optical counterparts appearing as unresolved point sources. • Unfamiliar optical emission lines. • Maartin Schmidt was the first to recognize that these lines were normal Hydrogen lines seen at much higher redshifts than any previously observed galaxies. • D = 660 Mpc (2.2 billion light years) for 3C273 • 1340 Mpc (4.4 billion light years) for 3C 48 • L = 2 x 1013 Lsun for 3C273. • Within ~2 years, quasars were discovered with: z > 2 and L  1014 Lsun • Most distant QSO discovered today - z = 6.42

  6. QUASAR -- Starlike – some time radio loud -- Variability (continuum) -- UV excess -- Broad Lines -- High z -- X-Ray emission -- continuum  non thermal (radio optical and X) radio quiet similar to radio loud, Radio to optical ratio: radio at 5 GHz – optical at 4400 Amstrong Rr-o = 10--100 radio loud = 0.1--1 radio quiet

  7. 3C 48

  8. 3C 273

  9. HST image 3C273

  10. Very Long Baseline Interferometry : VLBI EVN V L B A Spatial VLBI

  11. 1144+35

  12. Angular resolution: R = 1.22 lambda/D radiant eye D= 8 mm R = 17.3” but because of cell size 1’ Optical telescope 4 m: 0.035” but seeing problems…. Radio no problem with atmosphere up to 22 GHz and more  R better than 1 mas

  13. Linear scales SMBH ≈ AU Accretion Disk 1 mpc Compact radio VLBI core 0.1 pc BLR 1 pc Molecular Thorus 100 pc NLR up to kpc Host Galaxy a few kpc Radio Lobes 1 Mpc

  14. VLBI studies of radio galaxy nuclei :one of the most important results is the detection of proper superluminal motion Expansion of about 6 pc in 3.5 years:  velocity  6c

  15. By the time that light leaves from position (2), light emitted from position (1) will have travelled a distance AC The difference in arrival time for the observer is : SUPERLUMINAL MOTION The apparent velocity as seen by the observer is For example :  = 10o and v = 0.999c then : v(OBS) = 10.7 c

  16. The detection of superluminal motions and of one-sided jets in the majority of both low power and high power radio galaxies indicates that the jets at their basis are all strongly relativistic

  17. Doppler effect and relativistic boosting • v = βc θ orientation angle with respect to the line of sight •  o = e/((1-βcosθo)) = e D • is the Lorentz factor and • D = 1/((1-βcosθo)) = Doppler factor • Low velocity:  ≈ 1 D  (1 + β cosθo) classic Doppler • Le total source luminosity • monocromatic source luminosity L(e) • Power emitted in e will be received in • o = e D

  18. The power is: for frequency unit o = e x D for time unit dto = dte - dte  β cosθ = dte(1 – β cosθ) = dte/D in the time range between the emission of 2 photons the source moved in our direction (or time contraction) for solid angle: do = de/D2 Relativistic aberration and do ≈ π dθo2

  19. in conclusion Lo = Le x D4 Doppler boosting or relativistic beaming But if we consider monochromatic emission Lo(o)do = Le(e)de x D4 Lo(o) = Le(e) x D3 Since L()  - (synchrotron) Lo(o) = Le(o) x D3+ = Le(o) x D4 D-(1-) D-(1-) is the K-correction

  20. JET RELATIVISTIC EFFECTS (DOPPLER BOOSTING) : Doppler factor Jet pointing toward the observer is AMPLIFIED

  21. From the ratio between the approaching and the receding jet, the jet velocity and orientation can be constrained JET SIDEDNESS RATIO But if jets are a continuum emission, only the structure in the motion direction is affected (unidimensional motion):

  22. FR I - 3C 449 FR II - 3C 47

  23. Radio core dominance Given the existence of a general correlation between the core and total radio power we can derive the expected intrinsic core radio power from the unboosted total radio power at low frequency. Pc = observed core radio power at 5 GHz Ptot = observed total radio power at 408 MHz Core radio power affected by jet Doppler boosting Total radio power at low frequency is intrinsic, no boosting because core self –absorbed and radio lobes steep spectrum

  24. The comparison of the expected intrinsic and observed core radio power will constrain β and θ. A large dispersion of the core radio power is expected because of the dependance of the observed core radio power with θ. From the data dispersion we derive that Г has to be < 10

  25. Pc = Pi D(2+ ) Pbest-fit = P(60) = Pi D(2+ ) = Pi/2+(1-β cosθ)2+ if θ = 60 we have Pi/2+(1-β/2)2+ and Pi = P(60) 2+(1-β/2)2+ Pc = P(60) (1-β/2)2+ / (1-β cosθ)2+ Assuming  = 0 (nucleo) Pc = P(60) (1-β/2)2 / (1-β cosθ)2 (Pc/P(60))0.5 = (1-β/2)/ (1-β cosθ) Pc from observations P(60) from Ptot and best fit High jet velocity implies a high dispersion of observational points

  26. Arm length ratio By comparison of the size of the approaching (La) and receding (Lr) jet we derive: Or La/Lr = L’a/L’r = θa/θr = Da/Dr

  27. Brightness Temperature: I = F/πθ2 = B = 2kTb/2 F = observed monocromatic flux; θ source angular size. Values are in the range T ≈ 1011 – 1012 K  non thermal origin Tb has to be <= 1012 K since at this value the magnetic field energy density (Umag = B2/8π) can be lower than the radiation energy Urad = 4πJ/c When Urad > Umag the dominant emission is from inverse Compton in the gamma ray band and the source life is very short. Moreover we do not see the expected emission in the gamma band

  28. Therefore we derive that Urad/Umag < 1 corresponding to Tmax ≈ 1012 K or lower But from short (intraday variability) we have: Tb()  (S()/θ2) (2/2k)  S() 2 small θ and/or large Tb() > 1012 K Solutions: 1) Coherent synchrotron emission 2) Relativistic motion: Tbi = Tbo x D 3) Stellar scintillation

  29. THE MEASUREMENT OF THE JET VELOCITY Proper Motion In some sources proper motion has been detected allowing a direct measure of the jet apparent pattern velocity. The observed distribution of the apparent velocity shows a large range (e.g. Kellerman et al. 2000)

  30. From the measure of the apparent velocity we can derive constraints on β and θ: But are bulk and pattern velocity correlated???? In a few cases where proper motion is well defined there is a general agreement between the highest pattern velocity and the bulk velocity: Ghisellini et al. 1993 Cotton et al. 1999 for NGC 315 Giovannini et al. 1999 for 1144+35 However in the same source we can have different pattern velocities as well as standing and high velocity moving structures

  31. The correlation between the optical and radio nuclear flux density in FR I implies common synchrotron origin and no dust torus BL Lacs show the same correlation in agreement with Unified Models. The shift is due to the different boosting BL Lacs Chiaberge et al. 1999 FR I

  32. BL Lacs Chiaberge et al. 1999 FR I Our sample Corrected for the Doppler factor BL Lacs observed

  33. Parent Population intrinsic observed Low frequency  no beaming effects Nuclear properties different since are affected by beaming but in agreement if we compare intrinsic values.

  34. Velocity Structures An evident limb brightened jet morphology on the parsec scale is present in some FR I sources: 1144+35, Mkn 501, 3C 264, M87, 0331+39…….

  35. But also a few high power sources show the same structure BLAZAR 1055+018 The limb-brightened structure can be due to a different Doppler boosting in a two-velocity relativistic jet. If the source is oriented at a relatively large angle with respect to the line of of sight, the inner high velocity spine could be strongly deboosted while the slower external layer could be boosted or at least not so strongly de-boosted

  36. The low number of known limb-brightened sources is due: -- to observational problems to transversally resolve the jet -- to orientation effects: only sources in a small orientation range can appear as limb-brightened because of the different Doppler factor. Profile of the 3C 264 jet at different distances from the core BL_Lac 0521-165

  37. Is the two velocity regime ● related to the jet interaction with the ISM ● or an intrinsic jet property ? in most sources the limb-brightened structure starts far from the core  external (real or angular resolution effect?) in M87 the jet is limb-brightened on scales of light-weeks  intrinsic in Mkn 501 the jet is resolved very near to the core  intrinsic in 1144+35 we need a too fast velocity decrease  intrinsic

  38. Moreover recent observations of Cygnus A (Bach et al. 2003) show a complex structure of the jet and cj, an apparent jet acceleration and a low velocity proper motion. The observations could be explained by a stratification of the jet with different velocities. Meier (2003) discussed a model where a different velocity regime is an intrinsic jet property related to the inner AGN structure. In this case one more jet velocity decrease due to the ISM is likely to be present in an intermediate region (from the pc to the kpc).

  39. Two ‘laboratory’ sources: 1144+35 and Mkn 501 1144+35 is a giant radio galaxy: projected linear size 1.0 Mpc h65-1 The arcsecond core is the dominant feature

  40. On the parsec scale it shows a core, a strong extended jet and a short cj counterjet flat spectrum core main jet

  41. Superluminal motion Well defined components – 11 epochs from 1991 to 2002 Only high quality data: jet: 5 and 8.4 GHz data cj 8.4 GHz only Jet: βapp = 2.7 constant All components constant velocity cj side βapp = 0.3

  42. Since we know the j and cj proper motion according to Mirabel et al. 1994 we can derive the jet orientation: Assuming H0 = 65, the source distance D is 295 Mpc and θ = 25o Therefore β = 0.88 is the pattern velocity of the shear layer. The Doppler factor is 2.4 – the structure is boosted. From the j-cj brightness ratio and from the j-cj arm ratio we derive a jet bulk velocity β > 0.8 in agreement with the measured pattern velocity.

  43. Shear-layer δ = 2.4 - boosted If the inner spine is moving with e.g. Г = 15 the corresponding Doppler factor is 0.7 – deboosted. A fast spine and a lower velocity shear layer can explain the limb brightened structure. core If the external region started with the same velocity of the inner spine, its velocity decreased from 0.998 to 0.88c in less than 100 pc. This suggest a velocity structure already present at the jet beginning.

  44. z = 0.034 1mas = 0.67 pc Tavecchio et al. 2001 From NED

  45. Mkn 501 –Large Scale Koolgaard et al. 1992 VLA Symmetric structure Jets are no more relativistics on 10 kpc scale 20 kpc

  46. At 2 arcsecond β cosθ > 0.36 At 1 arcsecond β cosθ > 0.63 VLA B array (Cassaro et al. 1999) VLAA array at 1.4 GHz 1.5 kpc 1.5 kpc

  47. At100 mas:β cosθ > 0.61 At 50 mas: β cosθ > 0.77 HPBW = 9x5 mas 35 pc

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