Active galaxies. Some History Classification scheme Building blocks Some important results

Transcription

1 Active galaxies Some History Classification scheme Building blocks Some important results p. 1 Litirature: Peter Schneider, Extragalactic astronomy and cosmology: an introduction p , 5.1.1, 5.1.2, (excluding Synchrotron radiation), 5.1.4, 5.2, 5.3 (Introduction only), (excluding reverberation mapping), 5.4.3, p. 207 p. 2

2 History p. 3 Pioneering work by Karl Jansky in the 1930s and Grote Reber in 1940s Scientists and engineers involved in World-war II build dishes radio interferometers in Cambridge, Jodrell bank, Sydney and Parkes Grote Weber's original Radio Antenna Wheaton p. 4

3 1953: Cygnus A p. 5 Early 1980 p. 6

4 3C273 Beginning 1960 s: first reliable catalogues of radio sources with a few hundred entries 3C273: 273rd object (ordered by right ascension) of the Third Cambridge Catalog of Radio Sources (3C)." 1963: Accurate positions were obtained using lunar occultation by Cyril Hazard at the Parkes Radio Telescope. " The radio source was quickly associated with an optical counterpart, an unresolved 13th magnitude stellar object. Because of their star-like appearances, these powerful radio sources came to be called, for lack of a better term, quasi-stellar radio objects. This was soon shortened to "quasar."" 1963: The first spectrum of 3C273 was obtained by Maarten Schmidt using the Palomar 200" telescope. Schmidt puzzled over the photographic spectrum for months before he recognized that the strong, broad emission lines in the star were the familiar hydrogen-balmer series, but redshifted by 15%. It was not the 15% redshift that had puzzled Schmidt, galaxies were already known with much larger redshifts, but rather the brightness of 3C273. 3C273 was a thousand times brighter than even a very luminous galaxy would appear at a distance of 2 billion light years, corresponding to a redshift of 15.8%. p. 7 p. 8

5 p. 9 p. 10

6 3C 273 The "First" Quasar p. 11 Enormous luminosities Assuming the validity of the Hubble law, the redshift of z=0.158 for 3C273 implied a distance of ~ 500 Mpc, or a luminosity of L=10 12 L sun = 100 * Milky way Lsun = 4x1026 W! p. 12

7 Quasar variability down to light minutes! energy from small volume p. 13 Energy crises! Too much light production in too small volume Petrol efficiency : out Nuclear reaction efficiency 0.01 : out Gravity efficiency 0.1 : yes Conclusion: energy comes from gas falling towards a super massive star of a million solar masses (Hoyle and Fowler 1963) or a black hole! p. 14

8 Taxonomy p. 15 Nomenclature In the past 60 years, many types of `active' galaxies discovered, sometimes in different wavelength regimes: -optical -radio -near-ir -X-rays Result: a large number of (confusing) observationally based classes, some of which overlap. Important: distinguish between defining properties and subsequently measured properties and physical interpretations. Radio galaxies -broad line (FR2) -narrow line (FR1 and FR2) Quasars -radioloud -radioquiet -OVV (optically violently variable) BL Lacs Seyferts -Type 1 -Type 2 p. 16

9 Seyfert galaxies 1943, Carl Seyfert: certain nearby spiral galaxies have very bright, blue and pinpoint-like nuclei and unusual spectra with very strong, often broad, emission lines Most if not all Seyfert galaxies are in spirals Seyfert galaxy NGC p. 17 Seyfert I galaxies Observational characteristics High surface brightness nuclei Permitted lines of H, He I, He II, Fe II with widths up to 10 4 km/s High density gas electron density n e ~ 10 9 cm -3 Forbidden lines (e.g. [OIII]) much narrower: up to 10 3 km/s Low density gas: electron density n e ~ cm -3 Estimated size of broad-line region! 1 pc (BLR) BLR clouds have a small filling factor (10-7 ) p. 18

10 Seyfert II galaxies Only narrow lines observed Estimated size of narrow-line region pc (NLR) p. 19 Seyferts versus quasars QSOs are the more luminous counter parts of seyferts QSO: Nuclear magnitudes M B < Identification QSO s: unresolved at ~ 1 arcsec scales Seyferts: well resolved and identified with spirals p. 20

11 Radio Galaxies Powerful radio sources are frequently associated with giant elliptical galaxies. Intense beams or jets, moving with highly-relativistic speeds are transporting the electrons and magnetic field out to the radio lobes. The radio lobes are believed to be produced when the jets ram into intergalactic gas clouds. The radio emission is due to synchrotron emission and comes principally from giant radio lobes, well outside the visible portions of the galaxy, sometimes extending up to 1 Mpc. The jets can end in hotspots, intensity maxima at the extremities of the lobes. They have typical linear sizes of 1 kpc. Location where the jet hits the ambient medium Frequently there is also a radio core, coincident with the galaxy nucleus. p. 21 Cygnus A Cygnus A p. 22

12 AGN-1: HR-2007 p. 23 AGN-1: HR-2007 p. 24

13 Basis of radio classification 1. Morphological classification 2. Spectral classification Flat spectrum radio sources Steep spectrum radio sources 3. Variability 4. Optical spectra Narrow-line radio galaxies Broad-line radio galaxies (cf Seyfert I and qso) Feature less (link to blazars) p. 25 1a. Morphological classification: Lobe dominated Radio galaxies - Symmetric giant emission lobes, extending to Mpc scales - Host galaxy often elliptical (cf. Seyferts) Two classes: Fanaroff-Riley class II - morphological definition: edge-brightened lobes - invariably have high luminosities, L>10 32 erg/s/hz - steepest spectrum emission in inner region Fanaroff-Riley class I - morphological definition: edge-darkened lobes - lower-luminosity - smooth, continuous turbulent double-sided jets - steepest spectrum emission in outer region p. 26

14 FR I FR I: M84 VLA: 4.9 GHz Laing and Bridle 1989 p. 27 FR II: 3C175 VLA at 4.9 GHz Bridle et al p. 28

15 1b. Morphological classification: Core-dominated radio sources - strong radio emission from compact core - flat radio spectra - single-sided jet - milli-arcsec/pc scale jets observed with VLBI techniques - often superluminal motion p. 29 VLBI observations of Core dominated radio sources (Lister et al 2001) p. 30

16 2. Spectral classification Flat spectrum radio sources dominant nuclear emission Steep spectrum radio sources dominant lobe emission AGN-1: HR-2007 p variability: Blazars Blazars: a class consisting of BL Lacs and OVV s BL Lacs objects - Named after the proto-type - rapid and large variability - Optical spectrum: featureless powerlaw continuum - high polarization - superluminal motion on VLBI scales (superluminal motion: apparent movement on the sky larger than speed of light: this is caused by a relativistic effect when a blob of gas moves on a trajectory close to the line of sight at a speed close to the speed of light) - Interpretation: viewed along the jet Optically violently variable (OVV) quasars - BL lacs with with strong broad and narrow lines p. 32

17 Summary of properties p. 33 Building blocks p. 34

18 AGN at different scales from 1 Mpc to 10-4 pc p. 35 p. 36

19 p. 37 p. 38

20 p. 39 Unification Paradigm: all AGN powered by accretion onto super massive central black hole Unification schemes try to understand the differences among all kinds of AGN. Two types of schemes: 1. ``Intrinsic unification, where the differences are due to: Time evolution Black-hole mass Spin- black hole Environment/galaxy type 2. Orientation unification: observed properties are due to differences in viewing angle. - Angle-dependent emission: Due to Doppler boosting jet s and core are brighter when outflow is oriented along line of sight (Doppler boosting is a relativistic effect, resulting in synchrotron emission from particles moving towards the observer being relatively bright) - Angle-dependent obscuration: Class II sources are oriented such that a dusty torus obscures emission from the broad line region p. 40

21 Building blocks p. 41 p. 42

22 Important results Number densities of AGN AGN epoch AGN are short lived Black-hole mass galaxy mass relation Radio galaxy feedback p. 43 Local number density 5-10 % of quasars are radio loud p. 44

23 AGN epoch 2DF quasars Boyle etal 2000 p. 45 For example: AGN are short lived the speed with which hot-spots are inferred to move away from the galaxies is estimated to be 0.1 c. This leads to ages for radio galaxies with sizes of 100 kpc 1 Mpc of yrs, only <1 % of the age of the Universe p. 46

24 (triangles). respectively. Blackhole mass ~ Galaxy mass Adams et al p. 47 Radio galaxy feedback Energy deposited by powerful radio galaxies seems to stop star formation in massive galaxies so that they become red and not too massive. heat up cooling gas in clusters p. 48

25 Radio galaxy feedback Influence of radio source 3C84 on structure of X-ray gas in the associated cluster as observed with the Chandra X-ray satellite (Fabian et 2006) p. 49 Conclusion Galaxy formation is a complex process that needs to take into account physics operating on vastly different scales p. 50