AGN 1.1 Historical overview (Netzer chapter 1)
1.1.1 – The discovery of quasars
• Radio astronomy • Lunar occultations • The redshift interpretation
Radio telescopes -‐ Karl Jansky discovered, in 1931, tdescobriu ondas radio emission from the Milky Way -‐Modern antenas: Parkes (Au)
The precise location of radio sources: lunar occultations 3C 273 – the first Quasar (quasi-stellar objct) discoveredin 1963 Object 273 from the third Cambridge Catalog of radio sources
The spectrum of the first quasar: 3C 273 redshift z = Δλ/λ = v/c = 0.158 distance of 2.4 billion light-years luminosity = 1000 galaxies
Maarten Schmidt (1929-) in 1963
3C 279 - The variability and time-scale l ~ ct (a few light-months)
1.1.2 –The Seyfert galaxies
• Fath (1907) • Slipher (1917) • Hubble (1926 • Seyfert (1943) • Khatchikyan e Weedman (1971)
NGC 1068
• 1907 - Fath observou, no espectro de NGC 1068, 6 linhas em emissão, típicas de nebulosas planetárias.
• 1917 –Slipher obteve espectros melhores. • 1926 – Hubble obteve espectros de NGC 1068, NGC 4051 e NGC 4151. • 1943 – Carl Seyfert identificou 6 galáxias com núcleos semelhantes,
acrescentando NGC 1275, NGC 3516 e NGC 7469.
NGC 3516 NGC 4051 NGC 7469
The 6 “Seyfert galaxies” (1943) NGC 4151 NGC 1068 NGC 1275
Khatchikyan and Weedman (1971): Seyfert 1 e 2
1.1.3 – Identification of the first radio-galaxy
• Baade e Minkowski (1954): Cyg A
In 1954, W. Baade e R. Minkowski identified a radio-source with a weak galaxy at z=0.057 (Cyg A)
3C175 z=0.77 V=16.6 Cygnus A (3C405) z=0.056 V=17.0
The radio-galaxy Centaurus A
M 87
1.1.4 – LINERS (Low Ionization Nuclear Emitting Regions) • Heckman (1980)
1.1 5 – The continuum emission
• Quasares with strong radio emission(radio-loud): 10% Quasares with weak radio emission (radio-quiet): 90% Quasares emission in all spectral ranges
The average spectrum from more than 700 quasars
1.1.6 - Variability
• NGC 5548
Variability of NGC 4151 in the optical and X-Rays
1.1.7 – The AGNs zoo
AGN:
• QSO • Quasar • Radio-galaxy • NLRG • NLXG • Blazar (BL Lac object) • OVV • Seyfert Galaxy (type 1 and type 2) • LINER
How to find AGNs
• Radio (3C;PKS (Parkes); NVSS (NRAO VLA); FIRST).
• Optical – UV (Byurakan; Tololo; LBQS; Palomar QUEST; Palomar Green; 2DF; SDSS; GALEX).
• Infrared (IRAS; 2MASS; WISE)
• X-Rays (ROSAT; Chandra; XMM-Newton; Swift)
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