What are Active Galactic Nuclei?
What are Active Galactic Nuclei? Active Galactic Nuclei (AGN) are nuclei of galaxies which show energetic phenomena that cannot be clearly and directly attributed to stars.*
NGC 4151
* B. Peterson
QSO spectra
Radio loud
Radio quiet
Averaged spectral energy distribution (Elvis et al.1994)
QSO spectra
Radio loud
Radio quiet
Averaged spectral energy distribution (Elvis et al.1994)
QSO optical spectra
Francis et al. 1994
Summary on Broad line region ●
Dense (~109 cm-3) clouds within 1016..17cm (< 1 pc)
●
Filling factor ~10-7
●
Temperature ~10000 K
●
Covering factor ~0.1
●
Total mass O(M⊙)
●
~1010clouds with rcloud~1011 cm
●
Orbiting a massive central object
Narrow line region (NLR): Δv~400 km/s ●
Similar diagnostics as with BLR: –
ne~103 cm-3 (smaller than for BLR)
–
T~10000 K (generally slightly cooler than for BLR)
–
Filling factor ~10-2
–
NLR are spatially resolved r~100 pc
–
Properties change with r
–
No temporal variations observed
Image of the NLR NGC 5728
Note the asymmetry!
A. Wilson
The inner region (~100 pc) of an AGN ●
●
The narrow line region clouds are at ~100 pc distance Direct imaging with the Hubble space telescope reveals a ring of cold gas and dust in NGC 4261
Some examples for radio galaxies 3c272.1
500 000 lightyears
3c284
Beq(Lobes)~10 muG
Cygnus A (20 cm) 3c66 A&B
3c83.1B
NGC1275
Radio Galaxies ●
●
●
●
Generally: Elliptical galaxies, nuclear activity with radio emission – quite complex “zoo” for itself Radio spectra: –
Steep spectrum (extended): Sν~ν-0.5..-0.7
–
Flat spectrum (compact): Sν~ν0 or inverted spectrum
–
GigaHertz peaked sources
Optical spectroscopic classification (à la Sy): –
Broad Line Radio galaxies (BLRG)
–
Narrow Line Radio galaxies (NLRG)
Morphological classification (simplest form) –
Extended, double radio sources (Fanaroff-Riley I, II)
–
Compact, core dominated radio sources (often BL Lac, OVV)
Morphological classification of radio galaxies
●
Radio morphology is quite complex
●
Special terminology used
Morphological classification: Fanaroff-Riley ●
B. Fanaroff & J. Riley introduced two classes of extended radio galaxies based upon luminosity &morphology –
FR I: low power (1035 erg/s), edgebrightened lobes, asymmetric jets
Examples of FR I and FR II radio galaxies M87
3C315
3C296 3C28 4
3C22 3
3C43 8
Virgo A (M87)
M~3x109 M⊙
Precessing jet? Jet confinement Acceleration Composition of the jet Fastest variability at the highest energies
Unified scheme for AGN
Periscope effect: Observing the Sy 1 in the Sy 2
BLR can be seen in the reflection of gas. The reflected light is polarised!
Sy 2 galaxy NGC 1068 Miller et al. (1997)
Broad line regions “appear” in the spectrum of polarized light The polarization is strongest at the position of the nucleus: We see the BLR in reflected light
NGC 4151
* B. Peterson
QSO spectra
Radio loud
Radio quiet
Averaged spectral energy distribution (Elvis et al.1994)
QSO spectra
Radio loud
Radio quiet
Averaged spectral energy distribution (Elvis et al.1994)
QSO optical spectra
Francis et al. 1994
Summary on Broad line region ●
Dense (~109 cm-3) clouds within 1016..17cm (< 1 pc)
●
Filling factor ~10-7
●
Temperature ~10000 K
●
Covering factor ~0.1
●
Total mass O(M⊙)
●
~1010clouds with rcloud~1011 cm
●
Orbiting a massive central object
Narrow line region (NLR): Δv~400 km/s ●
Similar diagnostics as with BLR: –
ne~103 cm-3 (smaller than for BLR)
–
T~10000 K (generally slightly cooler than for BLR)
–
Filling factor ~10-2
–
NLR are spatially resolved r~100 pc
–
Properties change with r
–
No temporal variations observed
Image of the NLR NGC 5728
Note the asymmetry!
A. Wilson
The inner region (~100 pc) of an AGN ●
●
The narrow line region clouds are at ~100 pc distance Direct imaging with the Hubble space telescope reveals a ring of cold gas and dust in NGC 4261
Some examples for radio galaxies 3c272.1
500 000 lightyears
3c284
Beq(Lobes)~10 muG
Cygnus A (20 cm) 3c66 A&B
3c83.1B
NGC1275
Radio Galaxies ●
●
●
●
Generally: Elliptical galaxies, nuclear activity with radio emission – quite complex “zoo” for itself Radio spectra: –
Steep spectrum (extended): Sν~ν-0.5..-0.7
–
Flat spectrum (compact): Sν~ν0 or inverted spectrum
–
GigaHertz peaked sources
Optical spectroscopic classification (à la Sy): –
Broad Line Radio galaxies (BLRG)
–
Narrow Line Radio galaxies (NLRG)
Morphological classification (simplest form) –
Extended, double radio sources (Fanaroff-Riley I, II)
–
Compact, core dominated radio sources (often BL Lac, OVV)
Morphological classification of radio galaxies
●
Radio morphology is quite complex
●
Special terminology used
Morphological classification: Fanaroff-Riley ●
B. Fanaroff & J. Riley introduced two classes of extended radio galaxies based upon luminosity &morphology –
FR I: low power (1035 erg/s), edgebrightened lobes, asymmetric jets
Examples of FR I and FR II radio galaxies M87
3C315
3C296 3C28 4
3C22 3
3C43 8
Virgo A (M87)
M~3x109 M⊙
Precessing jet? Jet confinement Acceleration Composition of the jet Fastest variability at the highest energies
Unified scheme for AGN
Periscope effect: Observing the Sy 1 in the Sy 2
BLR can be seen in the reflection of gas. The reflected light is polarised!
Sy 2 galaxy NGC 1068 Miller et al. (1997)
Broad line regions “appear” in the spectrum of polarized light The polarization is strongest at the position of the nucleus: We see the BLR in reflected light
