AGN_grad - Active Galaxies and Related Objects What are...

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Unformatted text preview: Active Galaxies and Related Objects 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 Quasars • First discovered in the 1960s. • Detected radio sources with optical counterparts appearing as unresolved point sources. • Unfamiliar emission lines in optical spectrum. Quasar 3C273 optical image and spectrum Within ~2 years, quasars were discovered with z > 2 and L ≈ 10 L • 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 m B = 13, M B = -26 (10 12 L sun ) Quasars •M B < -23, strong nonthermal continuum, broad permitted (~10 4 km/s) and narrow forbidden (~10 2-3 km/s) 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. ...) 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 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. QSO spectra also reveal some absorption lines not associated with the quasar. These narrow absorption lines are caused by intervening galaxy halos between us and the QSO....
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AGN_grad - Active Galaxies and Related Objects What are...

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