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Transcript of AGN (Active Galactic Nuclei) - Max Planck Society · Magnetic field lines are coiled ... which...
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AGN(Active Galactic Nuclei)
Vera Genten
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Topics1)General properties
2)Model
3)Different AGN-types
I. Quasars
II.Seyfert-galaxies
III.Radio galaxies
IV.young radio-loud AGN (GPS, CSS and CFS)
V.Blazars
VI.LINER galaxies
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1. General properties
● AGN is the short form of ''active galactic nucleus''
● They have nearly a stellar shape on photographic plates.
● The visible emitting area is nearly as big as our solar system.
Broad band emission: i.e. from radiowaves, microwaves-infrared, visual ,ultraviolet- and x-ray to gamma radiation
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Assumption of the energy source for the extraordinary luminosity
● AGNs are the most luminous objects in the universe
● Assumption: a Black hole accretes gas and dust– Dissipative processes in the accretion disc transport
matter inwards and angular momentum outwards, while causing the accretion disc to heat up
● The resulting energy reaches nearly mc²
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Common galaxies gleam due to their stars in opposite to active
galaxies- they gleam due to their AGNs
common galaxy active galaxy
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2. Model
● A super massive, rotating – or not 'rotating – 'black hole'
with a mass up to 108-10 solar masses
● An accretion disk, surrounding the black hole
● Two Jets emerging from the center
● Broad-Line- and Narrow-Line regions
● Obscuring torus surrounds the accretion disk
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2.1 Regions
Broad-Line region (BLR)
● Above the accretion disk
● heavy ionized clouds– Become noticable with
very broad linesMovement 1.000-10.000
km/s
Narrow-Line region (NLR)
● Beyond the BLR● heavy ionized clouds
-Emissionlines in the spectrum less intensely dispread
Slower movement (ca. 100 km/s)
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2.2 Accretion disk
● A disk, rotating around the black hole, transports matter in the center
● Active galaxies differ thereby from common galaxies
● consists of normal gas or dust, or of ionized gas (->plasma)
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2.3 Radio-jets
● Consist of particles accelerated at nearly the speed of light (i.e. relativistic matter)
● Magnetic field lines are coiled (->by Frame-dragging in the ergosphere) – Arising a high magnetic pressure
– The matter is ejected but remains confined by the magnetic field
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JetSpirally arranged magnetic field lines
Black hole
Accretion disk
Creation of radio jets
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3. AGN- types
Which member you are observing depends on...
a) the angle between the observer and the object
b) the mass of the object
c) how much mass the black hole accretes
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Type dependent on observing angle
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3.1 Quasars
● among the most remote objects of the universe
– i.e. „SDSS 1030 + 0524“ is 14x10^9 lightyears away from the earth
● Distance meassured with redshift (->Appendix 1)
● Discovered by radio emission
● More information see Hendrik Gross
– > http://www.mpifr-bonn.mpg.de/public/massi/hendrikgross.pdf
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Hubble's law says, that the more distant an object is, the faster it is moving away from us.
The diagram shows the proportion velocity/distanceThe velocity of objects can be determined measuring their
redshift,
RedshiftAppendix 1
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3.2 Seyfert-galaxies
● named by the astronom Carl Keenan Seyfert
● Spiral- or irregular galaxies (->App. 2) with very luminous galactic nucleus (they can also emit gamma-rays).
● Seyfert-galaxies are of two types (Seyfert I and Seyfert II)
– They are AGN, as Quasars, but with a less massive black hole at the center
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Appendix 2
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●
● 2 different types:
– Seyfert 1-galaxies:'broad' line component (see 2.1)
– Seyfert 2-galaxies: just Narrow-Line region apparent
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Type1: BLR (intenser) and NLR (dimlier) visible
Type2: Obscuring torus disguises BLR
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3.2 Radio galaxies
Radio galaxy
● associated to Elliptical galaxie (-> App. 2)
● Radiation power in radio area exceed the radiation power in the visual spectral area
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● They could be identified among other dimly objects in the visible light, because...– The galaxy in the visible light is not outshined by
its core
●
nearest radio galaxy: Centaurus A (NGC 5128)
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In 1974, radio sources were divided by Fanaroff and Riley into two classes, now known as Fanaroff and
Riley Class I (FRI), and Class II (FRII).
FRI FRII
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3.3.1 Radio radiation
● The radio emission is synchroton radiation (emitted from electrons gyrating along magnetic field lines)
● The most common large-scale structures are called lobes: these are double, often fairly symmetrical structures placed on either side of the active nucleus.
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3.4 GPS
● Gigahertz peaked spectrum sources (=GPS)– Spectrum with convex form, peaks at ca. 1 Ghz
– High frequency peakers (HFP)● Like GPS, peak at >5 Ghz
● GPS galaxies are young radio sources (~100-1000 years old)
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CSS
● Compact steep spectrum sources (=CSS)
– ≤1“ in size, steep spectrum (->App.3), peak at ca. ≤100 MHz – not visible
– CSS sources are 10000-100.000 years old
CFS– Compact flat spectrum (=CFS)
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CSS (compact steep spectrum) CFS (compact flat spectrum)
GPS (gigahertz peaked spectrum)
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intense radio sources
Spectrum: radiation flux in dependence of radiation frequency
Appendix 3
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Blazars are a subset of AGN
They are divided into two groups:
optically violent variable quasars (OVV), and BL Lacertae (BL Lac) type objects,
which display extremely intense, broad and rapidly varying electromagnetic
emission, from radio to gamma-rays in some case
Angle between line of sight and jet axes of few degrees
3.5 Blazars
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BL-Lac objects
● Firstly detected by Cuno Hoffmeister in 1929
● 1968: detected as strong radio source
● Angle between jet axes and observing direction is very humble (direct view into the jet)
● Continuous spectrum without absorption- and emissionlines
● Strong emission in gamma-rays
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Some BL-Lac objects outshine the whole emitted light of the surrounding galaxy
in this case is impossible to determine their distance(-> App. 1)
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●
● Fast, variable luminosity of BL-Lac objects over the whole spectrum
●
● High polarisation (orientation of the oscillation of electromagnetic waves)
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3.7 LINER galaxies
● Connector of active and non-active galaxies● Optical emissionline-spectrum -> low level of
ionization