219 research outputs found
The Intermediate Line Region in AGN: a region "praeter necessitatem"?
As a consequence of improved S/N, spectral resolution and wavelength coverage
various authors have introduced, without strong justification, new emitting
regions to account for various emission line profile differences in AGN. The
so-called CIVlambda1549 intermediate line region (ILR) appears to be especially
ill-defined. We present observational evidence that suggests the ILR is
statistically indistinguishable from the classical narrow line region (NLR). We
present the results of theoretical models showing that a smooth density
gradient in the NLR can produce CIV and Balmer emission lines with different
widths. The putative ILR component has often been included with the broad line
profile in studies of CIV BLR properties. Failure to account for the composite
nature of CIV emission, and for the presence of sometimes appreciable NLR CIV
emission, has important consequences for our understanding of the BLR.Comment: 3 Figs. 1 Table, accepted for publication in Astrophysical Journal
Letter
No Evidence for a Aystematic FEII Emission Line Redshift in Type 1 AGN
We test the recent claim by Hu et al. (2008) that FeII emission in Type 1 AGN
shows a systematic redshift relative to the local source rest frame and
broad-line Hbeta. We compile high s/n median composites using SDSS spectra from
both the Hu et al. sample and our own sample of the 469 brightest DR5 spectra.
Our composites are generated in bins of FWHM Hbeta and FeII strength as defined
in our 4D Eigenvector 1 (4DE1) formalism. We find no evidence for a systematic
FeII redshift and consistency with previous assumptions that FeII shift and
width (FWHM) follow Hbeta shift and FWHM in virtually all sources. This result
is consistent with the hypothesis that FeII emission (quasi-ubiquitous in type
1 sources) arises from a broad-line region with geometry and kinematics the
same as that producing the Balmer lines.Comment: 12 pages, 1 table, 1 figure - accepted for publication in ApJ Letter
Balmer line shifts in quasars
We offer a broad review of Balmer line phenomenology in type 1 active
galactic nuclei, briefly sum- marising luminosity and radio loudness effects,
and discussing interpretation in terms of nebular physics along the 4D
eigenvector 1 sequence of quasars. We stress that relatively rare, peculiar
Balmer line profiles (i.e., with large shifts with respect to the rest frame or
double and multiple peaked) that start attracted attentions since the 1970s are
still passable of multiple dynamical interpretation. More mainstream objects
are still not fully understood as well, since competing dynamical models and
geometries are possible. Further progress may come from inter-line comparison
across the 4D Eigenvector 1 sequence.Comment: Accepted for publication in Astrophysics and Space Science, Special
Issue on Line Shifts in Astrophysics and Laboratory Plasm
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