Today. Practicalities

Transcription

1 Today Broad and narrow emission line regions Unification AGN and galaxy formation AGN-10: HR 2007 p. 1 Practicalities Exam Dates (?) Example of exam questions Mini-symposium Dec :45 Power points to Mario (soto@strw.leidenuniv.nl) before Dec 13 7 minutes plus 3 minutes questioning AGN-10: HR 2007 p. 2 1

2 Presentation For your object of your own choice How was it found? Give a brief description Classification Relevant characteristics Include nice images and/or spectra Discuss how studies of this object contributed to our general understanding of astrophysics Open questions Future work AGN-10: HR 2007 p. 3 AGN emission lines Observations Spectra Broad line spectra (5000 km/s) Narrow line spectra (500 km/s) Morphology of narrow emission emission line regions Main questions Physics of broad and narrow emission line regions AGN-10: HR 2007 p. 4 2

3 Literature Peterson: An introduction to Active Galactic Nuclei ,5.7,6.1,6.2,6.3 Background literature Astrophysics of Gaseous Nebulae and Active Galactic Nuclei D.E. Osterbrock, 1989 (ch. 1-5, ch. 11, 12) AGN-10: HR 2007 p. 5 Class I spectra Broad and permitted lines AGN-10: HR 2007 p. 6 3

4 Class 2 spectra: only narrow lines AGN-10: HR 2007 p. 7 Typical spectrum of a high redshift radio galaxy AGN-10: HR 2007 p. 8 4

5 Quasars - broad lines only Seyferts - Type 1: broad permitted and narrow forbidden lines - Type 2: narrow permitted and forbidden lines - Type 1.n: intermediate cases LINERS -only narrow lines and low-ionization states Radio-galaxies: BLRG and NLRG - BLRG usually Type NLRG fairly similar to Seyfert 2 AGN-10: HR 2007 p. 9 Example of a AGN with a Narrow line region NGC 1068 (z= ) Closest (14.4 Mpc), brightest and most studied (>200 titled refs) Seyfert galaxy 1 arcsec = 70 pc True-color'' image of the Seyfert 2 Galaxy NGC 1068 (UV, green, and red narrowband filters) Pogge & De Robertis; Reduction & Composition: Pogge] AGN-10: HR 2007 p. 10 5

6 UV and OIII HST images Complex Conical shape Beamed nuclear radiation Is being scattered Ionizes NL region 2 arcsec Macchetto et al 1994 F253M+F372M+F501N AGN-10: HR 2007 p. 11 Lya halos Luminous (10-15 erg/s/cm 2 = erg/s) Large: 200 kpc High velocity dispersion (~1000 km/s) In general associated with powerful radio sources, but not always Example: 4C41.17 at z=3.8 8 h keck NB filter: 200 kpc halo Reuland et al ApJ, 592, 377 AGN-10: HR 2007 p. 12 6

7 Questions I Ionization mechanism? Photo-ionization by a QSO Shock-ionization Gas cooling in a cooling flow Physical state? Density, temperature filling factor, neutral fraction, mass Metallicity Dust / CO distribution Structure? Cloudlets with a density structure Filaments What drives the kinematics? Gravity Shocks induced by radio jet Super winds buoyancy AGN-10: HR 2007 p. 13 Questions II What is the origin of the gas? Cooling flows Merger Central starburst wind Fate? Stars that will reside in the final galaxy Intra Galactic medium that will be enriched Address these questions through observations: - equivalent width (EW) - v, σ (or FWHM) - line ratios - all of these integrated along line of sight, and over aperture AGN-10: HR 2007 p. 14 7

8 Photoionisation Photo-ionization most likely for luminous AGN: - Observed ionization states require energy > kinetic energy in collisions - EW related to AGN continuum - Correlation variability AGN continuum and broad line flux - Ionization cones in Seyferts - Ionization extends outside radio-jets Photo-ionization must be caused by AGN itself: Hot stars do not produce the high-energy photons to give wide range of observed ionizations (HII through FeX) The number of photons that can ionise hydrogen: With L ν the qso spectrum Ionisation parameter is the ratio of photon to particle number density: Measure line ratios to determine U AGN-10: HR 2007 p. 15 Complete description of ensemble of emission lines depends on: - Input spectrum of ionizing photons - Geometry of gas and dust - P, T, n e - Abundances - Atomic properties - possibility of allowed, forbidden or semi-forbidden transitions Theory similar to that for HII regions and Planetary Nebulae, but input radiation field is now a power-law, not black-body Thermal equilibrium Heating - Photoionization - Minor contribution by shocks and massive stars Cooling - Collisionally-excited line emission - Free-free emission (Bremsstrahlung) - Radiation from recombination AGN-10: HR 2007 p. 16 8

9 Radiative transfer Escape of radiation depends on global properties - Extinction (absorption and scattering) by dust - Opacity of atoms dominated by H ground-state photoionization - Line transfer and line fluorescence AGN-10: HR 2007 p. 17 Physics of the broad-line region Relative line ratios indicate T ~ 10 4 K The line of sight velocity dispersion of 10 4 K gas: However, the derived temperature for ~ 5000 km/s is 10 9 K Physical picture is small cloudless having large relative speeds AGN-10: HR 2007 p. 18 9

10 [OIII] λ λ 4363, 4959, 5007 lines absent in broadline spectra The critical density for collisional de-excitation of the 1 S 0 in 0 ++ (upper level of the λ 4363 transition) is 10 8 cm -3 Hence the density is larger than 10 8 cm -3 The emissivity in the collisionally excited CIV line AGN-10: HR 2007 p. 19 Total cloud column density cm 3, solar abundances, typical AGN spectrum, electron density cm -3 (See p. 76 Peterson) AGN-10: HR 2007 p

11 Total luminosity With ε: filling factor, r radius of BLR And assuming all carbon triply ionised A cosmic abundance log[c/h] = Filling factor given a cloud size of Using a density of cm - 3, we get a very small filling factor: (for a typical Seyfert) AGN-10: HR 2007 p. 21 The mass of the broad line region is very small: Cross section of individual cloud: Covering factor ~ 10% and number of clouds: To get smooth profiles N c > 10 5, hence size < 400 R 0 Unclear what holds the clouds together External pressure by hot gas? Magnetic fields AGN-10: HR 2007 p

12 Summary BLR cloudless having relative speeds of ~ 5000 km/s T=10 4 K, n=10 11 cm -3 Filling factor 10-7, covering factor 10 % Mass small: 10-3 M o R ~ pc Light-travel time 0.1 yr variability observed Confinement mechanism is not clear AGN-10: HR 2007 p. 23 Narrow line region Consider the emissivity due a transition from level 2 -> level 1 With A 21 the einstein A coefficient for spontaneous emission AGN-10: HR 2007 p

13 The collisional excitation rate is balanced by collisional deexcitiaton and spontaneous emission: With σ ij the relevant velocity dependent collisional cross sections Taken together: Detailed balance: With g 1,g 2 statistical weights of the levels, T e electron temperature and χ threshold kinetic energy to collisionally excite to the n=2 level AGN-10: HR 2007 p. 25 Low density : So: With q 12 := < σ 12 v > collisional excitation rate Or : all collisional excitations lead to radiative deexcitations j ~ n 2 AGN-10: HR 2007 p

14 High density : Hence: De-excitation more likely through collision than through spontaneous emission j ~ n AGN-10: HR 2007 p. 27 Critical density Radiative and collisional de-excitation are comparable: Electric dipole transitions have critical densities > cm -3 Non electric dipole transitions (forbidden transition) have much lower critical densities, comparable to or higher than AGN emission line regions Hence photoionisation leads to strong lines AGN-10: HR 2007 p

15 AGN-10: HR 2007 p. 29 Two examples SII doublet to determine electron densities OIII triplet to determine electron temperatures AGN-10: HR 2007 p

16 SII line Two lines of one ion at very similar energy levels but different radiative and/or collisional de-excitation rates Also used - [O II] 3729/3726 AGN-10: HR 2007 p. 31 SII line AGN-10: HR 2007 p

17 AGN-10: HR 2007 p. 33 Electron temperatures Two lines of one ion that emit from quite different energy - Line ratio is temperature sensitive Often used: [O III]( )/4363 T in the range of K AGN-10: HR 2007 p

18 Emissivity in the Hβ line (relatively un-sensitive to T) Total luminosity: Size: With n 3 = n / (10 3 cm -3 ) Following the same method as for the BRL: Filling factor ~1 %, masses 10 6 M 0, N c 10 6 AGN-10: HR 2007 p. 35 Summary NLR 10 6 cloudless having relative speeds of ~ 500 km/s T=10 4 K, n=10 2 cm -3 Filling factor 1%, Mass small: 10 6 M o R ~ pc E(B-V) 0.5 mag Confinement mechanism is not clear AGN-10: HR 2007 p

19 Diagnostic diagrams Commonly used indicators: (Baldwin, Phillips & Terlevich 1981) [O III]/Hβ mean level of ionization and T [O I]/Hα relative importance of partially ionized zone [S II]/Hα caused by high-energy photo-ionization [N II]/Hα good separation between H II and AGN Solid curve: empirical dividing line Short-dashed: power-law continuum for Z and Z /10 Long-dashed: composite model AGN-10: HR 2007 p. 37 With Sloan survey AGN-10: HR 2007 p

20 Unification Paradigm: all AGN powered by accretion onto super massive central black hole Many different kinds of AGN observed: - Radio galaxies - Quasars - Seyferts Unification schemes try to understand these differences - Intrinsic? Time evolution Black-hole mass Spin- black hole Environment - Differences in viewing angle? (this is the ``narrow meaning of unification) - Angle-dependent emission (including relativistic beaming) - Angle-dependent obscuration (accretion disk) AGN-10: HR 2007 p. 39 General Literature - Krolik ch.12 - Robson ch. 9 - Kembhavi & Narlikar ch. 12 Specific papers Is every quasar beamed? - Barthel P.D., 1989, ApJ, 336, 606 Unified schemes for radio-loud active galactic nuclei - Urry C.M., Padovani P., 1995, PASP, 107, 803 Extragalactic results from the Infrared Space Observatory - Genzel R., Cesarsky C.J., 2000, astro-ph/ AGN-10: HR 2007 p

21 Intrinsic I Time evolution I Compact -> normal -> Mpc radio galaxies Compact radio galaxies (O dea, 1998, PASP, 110, pp ) GPS: GigaHerz Peaked spectrum radio galaxies» radio spectrum peaks at 1 GHz» pc radio sources CSS: Compact Steep Spectrum radio galaxies» 1-2 arcsec in size Mpc radio galaxies > 1 Mpc up to 5.7 Mpc in size AGN-10: HR 2007 p. 41 3C Mpc z= arcmin AGN-10: HR 2007 p

22 Intrinsic II Possible sequence of events leading to a quasar Merging of two galaxies compression in concentrated gas leads to massive starburst part of the gas sinks to the center and initiate starburst activity Only when dust and gas have been largely transformed into stars, galaxy becomes transparent and quasar is visible (e.g. Sanders et al 1988) AGN-10: HR 2007 p. 43 Intrinsic III Mass of the black hole radio power related to mass black hole due to adiabatic and synchrotron losses no one to one relation radio luminosity and mass blackhole Spin of the black hole related to radio loudness? related to FRI/FRII dichotomy? AGN-10: HR 2007 p

23 Intrinsic: environment Why are GPS and CSS sources so small? early stage of evolution: probably jet growth frustrated due to dense environment Bents and twists in radio sources jets changing direction interaction with clouds tailed radio sources interaction of jets from a moving galaxy with the surrounding (cluster) medium AGN-10: HR 2007 p. 45 3C 129 AGN-10: HR 2007 p

24 Orientation unification Observation ClassI versus II spectra Polarized broad lines in Class II Ionisation cones AGN-10: HR 2007 p. 47 Logical steps for (orientation) unification - Decide/choose which objects belong to one class - Determine which observables depend on inclination angle ψ, and predict ψ dependence of model - Compare with observed dependence in complete sample, where one can assume that ψ is random, and/or - Compare measurements at different ψ for same system (by use of reflection) AGN-10: HR 2007 p

25 Core- and lobe-dominated radio-loud quasars members of the same parent population? Orr & Brown (1982, MNRAS, 200, 1067) - Compact component: beamed (two symmetric jets) - Extended component: emission isotropic Quantify this idea, by defining with F b beamed component and F ext unbeamed component R t =R(ψ=π/2) and R depends on frequency ν Compute probability of observing R in [R, R+dR] for sample with randomly oriented symmetric jets, and compare with observations of radio quasars - Good agreement for R t» 0.024, γ» 5 - Predicts» correct fraction of flat spectrum quasars AGN-10: HR 2007 p. 49 AGN-10: HR 2007 p

26 Unification of radiogalaxies and quasars Barthel showed in 1989 that quasars and radiogalaxies can be considered one class of objects, with appearance governed by inclination see als Scheuer 1987 Assume FR II radiogalaxies and radio quasars are same population, seen from different angle: - 0 ψ ψ 0 : quasar, v>c one-sided jet - ψ 0 < ψ π/2: radio galaxy Barthel (1989, ApJ, 336, 606) - Use 3CR - Restrict to 0.5 < z < Ignore compact-steep spectrum sources - 29% quasars and 71% radio galaxies - Linear sizes: R» 2.2 R QSO AGN-10: HR 2007 p. 51 AGN-10: HR 2007 p

27 Random orientation of jet in parent population Barthel's sample: - Boundary quasars/radio galaxies 45 degree - <ψ>(quasars) ~ 30 degree - <ψ>(galaxies) ~70 degree - Predicted mean size ratio» 1.9: good agreement - Some discrepancies suggested for other z ranges, but later work shows that this picture is broadly consistent, in particular when taking into account that radiogalaxies and quasars evolve in size and luminosity AGN-10: HR 2007 p. 53 AGN-10: HR 2007 p

28 Galaxy formation and feedback Literature Best 2006 AGN-10: HR 2007 p. 55 Second data release (DR2) of the Sloan Digital Sky Survey (Stoughton et al. 2002) galaxies with magnitudes 14.5 < r < 17.77, for which spectroscopic redshifts have been determined. Measured parameters include: galaxy sizes; concentration indices; 4000-A break strengths; Hδ absorption measurements emission-line fluxes, parameters measuring optical AGN activity, such as emission-line ratios, and galaxy velocity dispersions Derived parameters include total stellar masses, stellar surface mass densities, mass-to- light ratios, dust attenuation measurements, star formation rates and gas-phase metallicities Black hole masses AGN-10: HR 2007 p

29 The NVSS (Condon et al. 1998) and FIRST (Becker et al. 1995) radio surveys Both 1.4 GHz, The NVSS covers the entirety of the sky north of declination, at an angular resolution of 45 arcsec, down to a limiting point source flux density of about 2.5 mjy. It is therefore sensitive to extended radio emission, The FIRST observations cover a sky area designed to largely overlap with that of the SDSS, down to a limiting flux density of about 1 mjy for point sources. These have a much higher angular resolution (4 arcsec) of allowing reliable crosscomparison of point sources, but meaning that extended sources are often resolved into multiple components, and some (or even all) of the flux density may be resolved out. AGN-10: HR 2007 p. 57 Sample with relevant properties well measured over a large range (Best et al. 2004) Z< 0.1, S > 5 mjy AGN-10: HR 2007 p

30 Radio loudness strong function of galaxy and BH mass This suggest that black holes form at high redshift together with their associated galaxies. AGN-10: HR 2007 p. 59 Energy input of AGN into the ISM AGN-10: HR 2007 p

31 Galaxy formation In hierarchical clustering models of galaxy formation, the growth of structure is controlled by the gravitational collapse of haloes of dark matter These merge together and accrete more mass to form progressively larger structures. The baryonic material, out of which stars and galaxies are formed, is superimposed upon this dark matter distribution. As gas falls into the gravitational potential well of dark matter haloes, it is initially shock--heated to the virial temperature of the halo. This energy is then radiated away, and the gas cools and condenses, and begins to form stars. The properties of the resultant galaxies can be determined using semi-- analytic models (e.g. White & Frenk 1991) AGN-10: HR 2007 p. 61 What is Feedback? Problem: many more massive galaxies predicted than observed Needed: additional heating source AGN-10: HR 2007 p

32 AGN feedback X-ray observations have revealed hot bubbles and cavities in the hot intracluster medium Deprojected 0.3 to 7 kev X-ray image of the center of the Perseus cluster, overlayed with contours from the 328 MHz VLA image at a resolution of 8 arcsec (Fabian et al. 2003) AGN-10: HR 2007 p. 63 Energy balance Energy production Fraction of the galaxies with active radio sources Mechanical energy production as evaluated by the pv energy associated with the cavities H = (M BH /M 0 ) 1.6 W Energy losses Cooling radiation losses of the hot gas associated with massive galaxies Determined using X-ray observations Conclusion: Radio feedback is likely to be important Best et al AGN-10: HR 2007 p

33 AGN feedback seem to solve the overcooling problem AGN-10: HR 2007 p. 65 OVERVIEW AGN-10: HR 2007 p

34 OVERVIEW AGN-10: HR 2007 p. 67 Future AGN-10: HR 2007 p

35 Future Observations LOFAR will detect and map all radio loud AGN Space interferometers like Darwin will make exquisite maps of tori up to high redshifts X-ray missions like Xeus will study the relativistic Fe lines up to redshifts z=8 Theory Detailed simulations of AGN elements: accretion disks, orbits close to BH, tori, and the merging sequences Incorporating joined evolution of AGN and galaxies into the large scale models AGN-10: HR 2007 p. 69 AGN-10: HR 2007 p