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Understanding Fe II Emission in AGN: Role of Fe Abundance

This study investigates the wide variations in optical Fe II emission among AGN and explores the role of Fe abundance in shaping these emissions. Results from composite spectra grouped by Fe II strength suggest that depletion of Fe into grains in the outer BLR might be a significant factor. Photoionization models, empirical correlations, and depletion patterns are analyzed to understand the observed Fe II range. The study also delves into the implications of Fe abundance for QSOs and early galactic chemical evolution.

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Understanding Fe II Emission in AGN: Role of Fe Abundance

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  1. Fe II Emission in AGN: The Role of Fe Abundance Gregory Shields , Randi Ludwig, SarahSalviander( arXiv:1006:2043)

  2. Abstract • Optical Fe II emission from BLR varies widely among AGN. • Composite spectra from SDSS grouped by Fe II strength allow measurement of weak narrow lines. Results rule out Fe/alpha and Fe/H as major cause of Fe II range. • Empirical correlations and photo-ionization models rule out X-ray strength as major cause. • Depletion of Fe into grains in outer BLR may be largely responsible.

  3. Intro • AGN show strong broad Fe II emission bands in optical and UV • Optical Fe II shows range 1.5 dex or more, UV somewhat less • Photoionization models have some success explaining Fe II emission but strongest Fe II is problematic. • Wide range of optical Fe II not understood. • Interest in Fe abundance in QSOs for early galactic chemical evolution.

  4. Iron Abundance • Photoionization models need enhanced Fe abundance to explain strongest Fe II objects. • Abundances in broad line region (BLR) are hard to measure. • Narrow line region (NLR) is easier. • [Fe VII]/[Ne V] good measure of Fe/Ne ratio (Nussbaumer & Osterbrock 1970) • Created composite SDSS spectra binned by Fe II/Hbeta to bring out weak • [Fe VII] line. • Results show insignificant trend in Fe/Ne with Fe II strength • Modest trend in [N II]/[S II] with Fe II strength suggests overall metallicity makes small contribution to range of Fe II strength.

  5. Fe VII and Ne V

  6. Trends with Fe II Strength

  7. Fe Depletion into Grains? • Fe/H down 1 -2 dex in ISM, planetary nebulae, H II regions. Depletions of other refractory elements vary. • Strong Fe II objects cannot have such depletions of Mg, Si, Fe (Gaskell, Shields, Wampler 1981) • Suggest that Fe depletion varies among AGN. • Dust sublimation may determine BLR radius (Netzer & Laor 1993). Indications of inflow from “dusty torus” to BLR; Fe II emission from outer BLR. • Photoionization models show optical Fe II linear in abundances, UV Fe II weaker dependence. • Raises questions about BLR relation to accretion flow, dust destruction processes, depletions of different refractory elements, BH masses.

  8. Abstract • Optical Fe II emission from BLR varies widely among AGN. • Composite spectra from SDSS grouped by Fe II strength allow measurement of weak narrow lines. Results rule out Fe/alpha and Fe/H as major cause of Fe II range. • Empirical correlations and photo-ionization models rule out X-ray strength as major cause. • Depletion of Fe into grains in outer BLR may be largely responsible.

  9. Abstract • Optical Fe II emission from BLR varies widely among AGN. • Composite spectra from SDSS grouped by Fe II strength allow measurement of weak narrow lines. Results rule out Fe/alpha and Fe/H as major cause of Fe II range. • Empirical correlations and photo-ionization models rule out X-ray strength as major cause. • Depletion of Fe into grains in outer BLR may be largely responsible.

  10. Radio Jet Interaction • Radio jets can affect the dynamics of the NLR and create double-peaked [OIII]. • J1517+33 (Rosario et al. 2010) • While 27% of our broad-line objects exhibit FIRST (limit 1 mJy) radio detection, it should be noted that an absence of detection does not necessarily mean there are no jets. VLA image of J1517+33

  11. Keck AO Images of Type 1 Binary Candidates C. Max et al. 2010 in progress

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