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Active Galactic Nuclei - AGN

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Active Galactic Nuclei - AGN Active galactic nuclei - AGN Carlo Ferrigno Department of astronomy - University of Geneva https://cms.unige.ch/isdc/ferrigno/ 2017 May 3 • history • Classification • Unified model History • 1908 E. fath notices strong emission lines from H, O, Ne in the nucleus of NGC 1068 • 1917 Emission lines are very broad in NGC 1068 (Slipher) • 1918 curious straight line in M 87 coming from centre • 1939 Radio source Cygnus A - Quasars (Quasi stellar radio sources) • 1943 Seyfert galaxies: strong broad emission lines and bright centre • 1954 Baade & Minkowski find the coun- terpart of Cygnus A to be at z = 0.057 • 1963 Schmidt localizes radio source 3C 273 at 1 arcsec (Lunar occultation) and counterpart to be at z = 0.158 Active Galactic Nuclei 1 • Thans to the interference pattern on the Moon edge, they found a double peak structure and determined the exact location of the radio source. • The more compact one was at the same position of the “star” with nebu- losity. • Schmidt et al. (1963) followed it up and found a large redshift of the lines., making the case for extra- galactic origin. From HAZARD et al. (1963). Active Galactic Nuclei 2 Normal vs Active galaxies • Extremely strong point-like source at the centre. In quasars, sometimes, the host galaxy is not seen. • Normally classified using emission line ratios (photo-ionization). • Ubiquitous X-ray emission !! Active Galactic Nuclei 3 Radio quiet and loud • If you optically select AGNs, you will always find a radio source, but this has different luminosity. • Radio loudness is ratio R = FR=FO, where FR is the monochromatic luminosity at 5 GHz and FO is the optical B-band at 440 nm. • two classes: one with R ∼ 0.1 − 1 and one with R ∼ 10 − 100. The boundary is set at R = 10. • radio-quiet are 10 times more. • radio-quiet are divided into low- luminosity Seyfert galaxies and high-luminosity quasars the bound- ary is at MB = −23 (absolute B-magnitude) From Kellermann et al. (1989). Active Galactic Nuclei 4 Radio loud - jets ! Jet from M 87 • current resolution might image the event horizon http://www. eventhorizontelescope.org/ • it was possible to follow these jets • radio loud sources have complex structure. Active Galactic Nuclei 5 Radio-loud classification Classification Fanaroff-Riley Classes (after their paper in 1974). FR1: • nucleus dominates • less luminous FR 2: • broad jets ending in plumes • luminosu radio sources • two asymmetric jets. • Lobes dominate • often only on-sided jets ending in radio lobes It is not clear the real origin of this difference. Active Galactic Nuclei 6 Blazars ‘ • A particular class of radio-loud objects are Blazars, which are point-like bright objects, featuring line-starved spectra • One type is BL Lac: erroneously classified as a star. Very bright optical source at centre of a galaxy without lines • One type is Optical violent variable (OVV) (∆m > 0.1 mag) • One type is flat spectrum radio quasars. Much brighter than BL Lac, and with spectrum with spectral index zero. • These objects are very bright throughout the full EM spectrum Active Galactic Nuclei 7 Optical classification - Seyfert Galaxies • Galaxies with line nuclear emission. • Seyfert 2 have forbidden narrow lines • They are also present in Sy 1, showing that Narrow line region is a common feature. Velocities are of 350–500 km/s, extension is 100–300 pc, and reach kpc 0.5 for bright objects (/ LX ) • Seyfert 1 have broad permitted lines Ve- locity of 1000–10000 km/s, with average around 5000 km/s. • Much higher than the temperature mea- sured from line ratios. It comes from dense moving clouds at 0.01–0.1 pc from the central source and increases 0.7 with luminosity (/ LX ). Broad Line Region.Covering fraction: 10%. Active Galactic Nuclei 8 Optical classification - Seyfert Galaxies Active Galactic Nuclei 9 Classification of narrow-line galaxies There are also Quasi-Stellar-objects, which are the core of the Galaxy, but with- out radio emission. Active Galactic Nuclei 10 Ionization cone [O III] ionization cone in NGC 5252 (from Dadina et al. 2010). • The NRL contains gas at n ∼ 103 cm−3 while BLR has n ∼ 1011 cm3. Active Galactic Nuclei 11 Summary From Pterson (1997) and Mazke et al. (1994) Active Galactic Nuclei 12 Unification • The line of sight determines the type of object at order zero. Active Galactic Nuclei 13 Active Galactic Nuclei 0–14a Bibliography HAZARD, C., MACKEY, M. B., & SHIMMINS, A. J. 1963, Nature, 197, 1037 Kellermann, K. I., Sramek, R., Schmidt, M., & Shaffer, D. B. 1989, Astron. J., 98 Dadina, M., Guainazzi, M., Cappi, M., et al. 2010, A&A, 516, A9 0.
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