AGN - Active Galaxies and Related Objects Chapter 19...

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Active Galaxies and Related  Objects Chapter 19 Centaurus A
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What are Active Galactic Nuclei (AGN)? Galaxies with a source of non-stellar emission arising in the nucleus (excessive UV, IR, radio and X-ray light) Central Black Hole accreting material from host galaxy (Lynden-Bell 1969) Quasars – luminous (M B <-23) objects with broad emission lines, distant, many are strong radio sources Seyferts – fainter (M B >-23), most identified locally, spiral hosts Sey 1s – broad emission lines (e.g. H balmer) Sey 2s – narrow emission lines Starbursts – Extreme starformation & blackhole accretion in the nucleus Radio Galaxies – display excess radio emission and jets LINERs – transition objects with ionization signatures between those caused by accretion onto a blackhole and starformation
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Quasars First discovered in the 1960s. Detected radio sources with optical counterparts appearing as unresolved point sources. Broad optical emission lines Quasar 3C273 optical image and spectrum
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Maartin Schmidt was the first to recognize that these lines were normal Hydrogen lines seen at much higher redshifts than any previously observed galaxies. In 3C273, H α ( λ rest = 656.3 nm was observed at 760.0 nm) z = 0.158 Wavelength shift of 15.8% means that in the time it takes light to reach us from 3C273, objects in the Universe have increased separation by 15.8%. d/c = 0.158 (1/H o ) Then d = 677 Mpc Absolute magnitude is then found by m - M = 5 log (d/10pc) = 39.0 Thus, since m = 13 for 3C273, M = -26 (10 12 times brighter than the Sun!)
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Quasars •M B < -23, strong non-stellar continuum, broad (~10 4 km/s) permitted and narrow (~10 2-3 km/s) forbidden emission lines Gravitational force required to prevent rapidly moving clouds that produce these broad emission lines from escaping the nucleus ~ 10 8 – 10 9 M sun •Radio quiet (RQQ): elliptical or spiral host galaxies •Radio loud (RLQ): 5-10% of all quasars, elliptical hosts • R L = log(L radio /L opt ) • Radio components for RLQs are 1-2 orders of magnitude brighter than radio galaxies (coming up next .... )
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SDSS BALQSOs from Trump et al. 2006 •Broad Absorption Line (BAL) Quasars: normal quasars viewed at angle along the l.o.s. of intervening, fast-moving material. • High-ionization (HIBAL): Ly α , NV, SiIV, CIV • Low-ionization (LOBAL): AlIII, MgII
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Quasar host galaxies difficult to detect due to brightness of AGN appear to be a mixed bag of galaxy types - from disturbed galaxies to normal E’s and early type spirals (though brightest QSOs tend to be in E’s)
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QSO spectra also reveal some absorption lines not associated with the quasar at all. These narrow absorption lines are caused by intervening galaxies (halos) between us and the QSO. Lyman Alpha Forest Redshifts of the material will be equal to or less than the QSO. Lyman alpha is the lowest excitation level for Hydrogen gas.
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short exposure long exposure NGC 4151 NGC 4151
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Seyfert 1s : Broad and  narrow lines (BLAGNs) Seyfert 2s : Only narrow  lines (NLAGNs) Seyfert galaxy spectra fall into two classes broad & narrow emission line spectra (like quasars – Seyfert type 1) narrow emission line only spectra (Seyfert type 2)
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