Radio Galaxies. D.Maino. Radio Astronomy II. Physics Dept., University of Milano. D.Maino Radio Galaxies 1/47

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1 Radio Galaxies D.Maino Physics Dept., University of Milano Radio Astronomy II D.Maino Radio Galaxies 1/47

2 Active Galactic Nuclei AGN: nuclei of galaxies with energetic phenomena that can not clearly and directly attributed to stars D.Maino Radio Galaxies 2/47

3 Active Galactic Nuclei Luminous UV emission from compact region in the center Doppler-broad emission lines High variability of days,months time scales Non-thermal emission Compact Radio Core Extenced linear radio structures (jets+hotspots) X-ray, γ-ray and (also) TeV emission CR production D.Maino Radio Galaxies 3/47

4 History of AGN Two main classes of AGN: Seyfert galaxies: often spiral with L L gal Quasars: often elliptical with L > 100 L gal D.Maino Radio Galaxies 4/47

5 History of AGN 1908: Fath& Slipher detect strong emission lines similar to PN with width of few 100km/s in NGC 1068 D.Maino Radio Galaxies 5/47

6 History of AGN: Seyfert galaxies Galaxy centers show broad lines High-excitation emission lines What is the source of broad lines? D.Maino Radio Galaxies 6/47

7 History of AGN: First detection of Optical jets 1923: Curtis detected jets in M87 D.Maino Radio Galaxies 7/47

8 History of AGN: Hubble discovery 1926: Hubble discovers the expansion of the universe nebulae are indeed extra-galactic objects 1943: Seyfert finds multiple galaxies similar to NGC1068 (hence their name) 1955: Detector of radio emission from NGC : First insight on Seyfert galaxies (Woltjer): unresolved nuclei (< 100pc) nuclear emission last for > 10 8 yr (1/100 of spirals are Seyfert and universe is yr old) nuclear mass is high if broadening is caused by bounded material (M v 2 r/g 10 9 M ) D.Maino Radio Galaxies 8/47

9 History of AGN: first Radio Surveys Early radio surveys played a crucial role in discovering quasars 3C: third cambridge catalogue (1959) at 159MHz (> 9Jy) basis for extra-galactic radio astronomy, cosmology and quasars! PKS: Parkes (> 4Jy) (> 1Jy) 4C: fourth cambridge (now 8): deeper/smaller AO: Aricibo Occulation survey Mostly normal galaxies (i.e. thermal emission of spirals) Stars with strange broad emission lines D.Maino Radio Galaxies 9/47

10 Radio Galaxy Emission Typical ( normal ) radio emission from a galaxy is due to: synchrotron radiation: e and other c-rays moving in the galactic magnetic field - S ν 0.7/ 0.9 free-free emission from Hii regions - S ν 0.15 thermal emission from dust heated by stellar radiation - S B(T )ν 1.5 D.Maino Radio Galaxies 10/47

11 History of AGN: Discovery of Quasars 3C273: the 273 source in the 3C catalogue Compact radio sources, star like but for a wisp of light D.Maino Radio Galaxies 11/47

12 Radio Properties of Quasars Although quasars discovered with radio they always are quite faint at radio wavelenghts Two main components: Compact: < 1 with flat spectrum, optically thick and also have clear optical source Extended: usually double lobes with steep spectra and optically thin D.Maino Radio Galaxies 12/47

13 Classes of (extended) Radio-Galaxies Large radio-galaxies with lobes can be divided into two types from Fanaroff-Riley (1974) FRI: weaker radio sources, bright at the center and fainter toward the edges FRII: collimated jets with hotspots L 1.4GHz = ergs/s/hz D.Maino Radio Galaxies 13/47

14 Classes of (extended) Radio-Galaxies D.Maino Radio Galaxies 14/47

15 The Zoo of AGN Diagnostic via BPT (Baldwin, Phillips & Telervich) diags. Why these lines? In general lines are sensitive to different parameters affecting the ISM (T, ρ, ionizing field, etc.) [OIII]/[OII]: is sensitive to ionization parameter (i.e. how the gas is ionized) [OI]/H α : is sensitive to hardness (energy) of radiation field D.Maino Radio Galaxies 15/47

16 The Zoo of AGN: Seyfert Seyfert type depends on the width of the optical lines Sy2: narrow emission lines FWHM few 100km/s Sy1: broad permitted lines (Hα,HeII,..) of δv < 10 4 km/s from high density n e > 10 9 cm 3 and narrow forbidden lines ([OIII],[NII]) from low density n e cm 3 Sy1.x(1.9,1.8,..): increase with width of Hα and Hβ lines NL Sy1: subclass of Sy2 with X-ray excess and optical FeII emission D.Maino Radio Galaxies 16/47

17 The Zoo of AGN: Quasars and QSO Quasars: Quasi Stellar Radio sources QSO: Quasi Stellar Object Scaled version of Seyfert where nucleus is very luminous M b < 21.5 Often star-like Spectra similar to Sy 1 but with weaker NL Either Radio-Loud QSOs or Radio-Quiet QSOs with transition at P 5GHz W/Hz/sr. RL QSOs are only 5-10% of total QSOs D.Maino Radio Galaxies 17/47

18 The Zoo of AGN: BL Lac BL Lac: is the protorype of its class. Star like with very weak emission lines and variable, intense and polarized continuum. Lines appear during quiescent phases Blazars: Encompass BL Lacs and optically violent-variable (OVV) QSOs. Strong relativistically beamed jet along the los D.Maino Radio Galaxies 18/47

19 Unification Scheme? Postulate a standard model for the structure of AGN Radio galaxies, quasars, QSOs, Seyfert, BL Lacs are indeed the same type of object what s the origin of the difference? The angle is everything: viewing angle makes the differnce Centre of a galaxy is a Black Hole surrounded by an accretion disk, together with clouds of gas and a dusty torus Energy output comes from accretion of material onto the BH D.Maino Radio Galaxies 19/47

20 Unification Scheme! D.Maino Radio Galaxies 20/47

21 Standard Model of AGN Accretion disk: r 10 3 pc, n cm 3 and v 0.3c Broad Line Region: r pc, n cm 3 and v few 10 3 km/s Torus: r 1 100pc, n cm 3 Narrow Line Region: r pc, n cm 3 and v few 100km/s D.Maino Radio Galaxies 21/47

22 Unification of AGNs D.Maino Radio Galaxies 22/47

23 Support to Unification BLR near nucleus is obscured by torus in Sy2. Hot scattered e from BLR can arrive to observer Sy2 is like Sy1 in polarised light Ionization cones: UV emission comes from the accretion disk and light up a cone of gas away from the torus that absorbs part of it All Seyfert galaxies have a NLR with very similar properties Size of Sy 1 continuum emitting regions are smaller than those of Sy 2 Direct image of torus D.Maino Radio Galaxies 23/47

24 Image of Torus D.Maino Radio Galaxies 24/47

25 FIR/Radio Correlation Van der Kruit (1971) discovered a correlation in a Seyfert (AGN) galaxy between luminosity at 10µm and at 1415 MHz Extended and verified for normal galaxies thanks to the IRAS satellite from which ( ) ( ) FIR 2.58 Wm 2 = S60µm + S 100µm Jy total flux 40µm < λ < 120µm Define ( q log FIR Wm 2 ) ( log S ν Wm 2 Hz 1 q log version of ratio: σ q 0.2 and q = 2.3 at 1.4 GHz ) D.Maino Radio Galaxies 25/47

26 FIR/Radio Correlation D.Maino Radio Galaxies 26/47

27 Radio Galaxies Cyngnus A from 2cm D.Maino Radio Galaxies 27/47

28 Why Study Radio-Loud AGN? Comparison between radio-load AGN and optical AGN samples origin of radio-loudness Some radio and soft X-ray AGN show little or no line emission include AGN missed from emission-line selection Radio activity is an efficient mean of feeding AGN energy directly back into environment (e.g. sound waves) role of AGN feedback on environment Radio galaxies and Radio-loud quasars are the most powerfull radio sources but radio is a small fraction of the total amount of energy 10 4 of optical output D.Maino Radio Galaxies 28/47

29 Derive SED from radio surveys There are several mechanism acting to contribute to the SED: relativistic e can loose energy by adiabatic expansion, synch. inverse Compton, etc We already know that N(E) varies with time both for adiabatic expansion (decrease in L but spectrum unchanged) and by radiation E = B 2 t 1/2 ν break B 3 t 2 yr For ν < ν break spectra index is unchanged For ν > ν break α = α 0 1/2 D.Maino Radio Galaxies 29/47

30 Derive SED from radio surveys Energy lost affects mainly large scale structures (e.g. lobes) Typical α = 0.7 for radio lobes ( ) B 3/2 ( ν ) 1/2 t 1/2 = Myr µg GHz D.Maino Radio Galaxies 30/47

31 Self-absorption in the relativistic e gas Optically thick case: consider internal absorption of e T b is close to the kinetics temperature of e Opacity larger at lower ν plasma opaque at low-ν and transparent at high τ 1 S(ν) ν 5/2 B 1/2 dω Mainly in the central compact region or very small radio sources Higher turnover frequency smaller size of emitting region D.Maino Radio Galaxies 31/47

32 Self-absorption in the relativistic e gas D.Maino Radio Galaxies 32/47

33 Polarization Synchrotron emission is highly polarized For an uniform B, the polarization of an ensemble of e is linear, normal to B and with fraction p = 3α + 3 3α + 7 Expected aroung 70-80% with 2 < α < 4 but observed up to 20% tangled B D.Maino Radio Galaxies 33/47

34 Different types of Radio Galaxies Morphology of radio galaxies could be different for several reasons: radio power propably related to AGN power orientaton of the radio emisson instrinsic differences in the (nuclear regions of ) host galaxy environment D.Maino Radio Galaxies 34/47

35 Different types of Radio Galaxies D.Maino Radio Galaxies 35/47

36 Different types of Radio Galaxies Morphology does not depend on size D.Maino Radio Galaxies 36/47

37 Different type of Radio Galaxies Interaction with environment D.Maino Radio Galaxies 37/47

38 Fanaroff-Riley Type I and II FRII: high radio power with very bright edges (hot-spots) collimated jets, B to jets, high Mach number (supersonic jet) backflow steep spectral index from hot-spot to nucleus FRI: low radio power large opening angle jet, B to jets, low Mach number fain lobes spectral index steep away from nucleus D.Maino Radio Galaxies 38/47

39 Fanaroff-Riley Type I and II Reasons for differences are not totally clear; likely related to nuclear region Different seen also in other wavebands Possible impact from environment: low-power radio galaxies are usually in clusters Not only morphological but also physical: strong separation in M b F 1400 plane D.Maino Radio Galaxies 39/47

40 Source of AGN power Main source is accretion onto the central BH Before entering matter is heated by friction to high temperatures (X-ray emission) BH radius is R S = 2GM BH c 2 = few light hours Energy available for a mass m at distance R S? E max = GM BHm R S = 1 2 mc2 Half the rest energy of the infalling mass is converted into kinetic energy If mass is decelerated by friction KE into thermal energy with efficiency η < 0.5 (usually η = 0.1) D.Maino Radio Galaxies 40/47

41 Source of AGN power Since L is de/dt for an AGN we have L = η dm dt c2 The MW has a luminosity of 1000L dm/dt 10 9 M /yr If with η = 0.1 we assume 1M per year we will have L = η dm dt c2 = ( ) 2 = L 100 times brighter than the entire MW D.Maino Radio Galaxies 41/47

42 The Eddington limit This is the maximum L for a given BH mass Two forces in balance: outward flow of photons gravitational force from infall material du dt = p ρ Φ = 0 If pressure is dominated by radiation with flux F p ρ = k c F where k = σ T /m p is the opacity (for hydrogen) If opacity is constant, with Gauss Theorem and Poisson eq. L = c Φ ds = c 2 ΦdV = 4πGc ρdv = 4πGMc k s k V k v k D.Maino Radio Galaxies 42/47

43 The Eddington limit Subs. the expression for k we obtain L Edd = 4πGMm ( ) pc M = L σ T M Evidence of SMBH found in most galaxies Relation between BH M and M b and σ e D.Maino Radio Galaxies 43/47

44 Superluminal motion Some radio-galaxies, BL Lac and Quasars show evindence of jets (or part of them) apparently moving faster than light Observed in 1970 and was used to move Quasar from cosmological distance: optical illusions plausible within SR They are indeed optical illusions but Quasars are at cosmological distances! D.Maino Radio Galaxies 44/47

45 Superluminal motion What is important here is the angle between jet and line-of-sight The jet is moving with v c along AB. At time t 1 a ray from the jet starts in A while at t 2 another ray starts at B. Observing times are t 1 and t 2 Elasped time is δt so AB = vδt and we can find AC and BC t 2 = t 2 + D L /c, t 1 = t 1 + D L /c + vδtcosθ/c δt = δt + vδtcosθ/c = δt (1 βcosθ) D.Maino Radio Galaxies 45/47

46 Superluminal motion The apparent jet motion is BC = D L sinφ D L φ But D L φ = vδtsinθ and the apparent transverse velocity v T along BC is v T = φd L δt = vsinθ 1 βcosθ β T = v T c = βsinθ 1 βcosθ D.Maino Radio Galaxies 46/47

47 Superluminal motion Find angle θ for maximum β T β T θ = 0 cosθ max = β sinθ max = 1 β 2 = 1 γ βmax T = βγ Therefore for γ 1 - the jet is moving with v c - even if β < 1 one can get βt max > 1 and hence superluminal motion since v T is the only velocity we can measure. D.Maino Radio Galaxies 47/47