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Fe II emission spectra in AGN: observations and theoretical interpretation

Verner, Ekaterina; Bruhweiler, Frederick; Johansson, Sveneric LU and Peterson, Bruce (2009) 9th International Conference on Atomic Spectroscopy and Oscillator Strengths for Astrophysical and Laboratory Plasma In Physica Scripta T134.
Abstract
The enrichment of Fe, relative to alpha elements such as O and Mg, represents a potential means to measure the ages of quasi-stellar object (QSO) host galaxies and probe nucleosynthesis in the early universe. QSOs exhibit prominent Fe II features and Mg II 2800 angstrom resonance doublet emission in the ultraviolet. Although chemical evolutionary models predict that the Fe/Mg abundance ratio decreases with increasing redshift, measurements of QSO Fe II (UV)/Mg II emission line ratios show large scatter from 1 to 20, with no redshift dependency up to z similar to 6.4. Before using Fe II emission as an abundance indicator, one must ascertain how Fe II emission varies with physical conditions. We have constructed an 830-level model atom for... (More)
The enrichment of Fe, relative to alpha elements such as O and Mg, represents a potential means to measure the ages of quasi-stellar object (QSO) host galaxies and probe nucleosynthesis in the early universe. QSOs exhibit prominent Fe II features and Mg II 2800 angstrom resonance doublet emission in the ultraviolet. Although chemical evolutionary models predict that the Fe/Mg abundance ratio decreases with increasing redshift, measurements of QSO Fe II (UV)/Mg II emission line ratios show large scatter from 1 to 20, with no redshift dependency up to z similar to 6.4. Before using Fe II emission as an abundance indicator, one must ascertain how Fe II emission varies with physical conditions. We have constructed an 830-level model atom for Fe II and used it in a photoionization code to calculate Fe II emission. This model is more sophisticated than previous efforts, and uses the most recent laboratory atomic data and includes the numerous transitions that are sensitive to the strong radiation field in QSOs. Predicted Fe II(UV)/Mg II ratios and fluxes strongly depend on non-abundance factors such as microturbulence, ionizing flux, and hydrogen density; all must be taken into account before any accurate abundance can be derived. Our calculations show that Fe II is the dominant coolant at densities found in active galactic nucleus (AGN) broad emission line regions (BLRs), and must be included in photoionization modelling. Our close collaboration with spectroscopists at Lund University has been highly beneficial for further development of our Fe ii model, most importantly through atomic data studies that link high-energy levels in Fe ii. Additional studies of the atomic structure of Fe ii are necessary to improve our understanding of the AGN continua by accounting for the effects of the Fe ii pseudo-continuum, which blanket QSO spectra from 1000 to 10 000 angstrom. Predicted Fe ii emission spectra, suitable for BLRs in AGN, are available at http://iacs.cua.edu/people/verner/FeII. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Chapter in Book/Report/Conference proceeding
publication status
published
subject
in
Physica Scripta
volume
T134
publisher
IOP Publishing
conference name
9th International Conference on Atomic Spectroscopy and Oscillator Strengths for Astrophysical and Laboratory Plasma
external identifiers
  • wos:000267612800007
  • scopus:70350625533
ISSN
1402-4896
0031-8949
DOI
10.1088/0031-8949/2009/T134/014006
language
English
LU publication?
yes
id
b693580e-dd5c-4759-9025-9e5acb4ef06c (old id 1462944)
date added to LUP
2009-08-18 16:48:56
date last changed
2017-04-16 03:31:02
@inproceedings{b693580e-dd5c-4759-9025-9e5acb4ef06c,
  abstract     = {The enrichment of Fe, relative to alpha elements such as O and Mg, represents a potential means to measure the ages of quasi-stellar object (QSO) host galaxies and probe nucleosynthesis in the early universe. QSOs exhibit prominent Fe II features and Mg II 2800 angstrom resonance doublet emission in the ultraviolet. Although chemical evolutionary models predict that the Fe/Mg abundance ratio decreases with increasing redshift, measurements of QSO Fe II (UV)/Mg II emission line ratios show large scatter from 1 to 20, with no redshift dependency up to z similar to 6.4. Before using Fe II emission as an abundance indicator, one must ascertain how Fe II emission varies with physical conditions. We have constructed an 830-level model atom for Fe II and used it in a photoionization code to calculate Fe II emission. This model is more sophisticated than previous efforts, and uses the most recent laboratory atomic data and includes the numerous transitions that are sensitive to the strong radiation field in QSOs. Predicted Fe II(UV)/Mg II ratios and fluxes strongly depend on non-abundance factors such as microturbulence, ionizing flux, and hydrogen density; all must be taken into account before any accurate abundance can be derived. Our calculations show that Fe II is the dominant coolant at densities found in active galactic nucleus (AGN) broad emission line regions (BLRs), and must be included in photoionization modelling. Our close collaboration with spectroscopists at Lund University has been highly beneficial for further development of our Fe ii model, most importantly through atomic data studies that link high-energy levels in Fe ii. Additional studies of the atomic structure of Fe ii are necessary to improve our understanding of the AGN continua by accounting for the effects of the Fe ii pseudo-continuum, which blanket QSO spectra from 1000 to 10 000 angstrom. Predicted Fe ii emission spectra, suitable for BLRs in AGN, are available at http://iacs.cua.edu/people/verner/FeII.},
  author       = {Verner, Ekaterina and Bruhweiler, Frederick and Johansson, Sveneric and Peterson, Bruce},
  booktitle    = {Physica Scripta},
  issn         = {1402-4896},
  language     = {eng},
  publisher    = {IOP Publishing},
  title        = {Fe II emission spectra in AGN: observations and theoretical interpretation},
  url          = {http://dx.doi.org/10.1088/0031-8949/2009/T134/014006},
  volume       = {T134},
  year         = {2009},
}