7,127 research outputs found
A Balmer-line Broad Absorption Line Quasar
I report the discovery of blueshifted broad absorption line (BAL) troughs in
at least six transitions of the Balmer series of hydrogen (Hbeta to H9) and in
CaII, MgII and excited FeII in the quasar SDSS J125942.80+121312.6. This is
only the fourth active galactic nucleus known to exhibit Balmer absorption, all
four in conjunction with low-ionization BAL systems containing excited Fe II.
The substantial population in the n=2 shell of H I in this quasar's absorber
likely arises from Ly-alpha trapping. In an absorber sufficiently optically
thick to show Balmer absorption, soft X-rays from the quasar penetrate to large
\tau_Ly\alpha and ionize H I. Recombination then creates Ly-alpha photons that
increase the n=2 population by a factor \tau_Ly\alpha since they require about
\tau_Ly\alpha scatterings to diffuse out of the absorber. Observing Ly-alpha
trapping in a quasar absorber requires a large but Compton-thin column of gas
along our line of sight which includes substantial H I but not too much dust.
Presumably the rarity of Balmer-line BAL troughs reflects the rarity of such
conditions in quasar absorbers.Comment: AJ in press. 4 pages, 1 figure, 1 table, emulateapj forma
VLT Observations of Two Unusual BAL Quasars
Among the unusual broad absorption line quasars being found by the Sloan
Digital Sky Survey (SDSS) are objects with much stronger absorption in Fe III
than Fe II. These unusual line ratios require a high density in the outflow
(n_H >= 3 x 10^{10} cm^{-3}). They should also appear for only a limited range
of outflow column densities, which explains their rarity. Previously we
suggested that the Fe III line ratios were also affected by a resonance; we now
believe this is an artifact of structure in the underlying Fe II + Fe III
pseudocontinuum. The SDSS is also discovering objects with absorption in rarely
seen transitions such as He I. VLT+UVES high-resolution spectra of one such
object, the mini-BAL quasar SDSS 1453+0029, show that it has two He I
absorption systems with considerably different properties separated by only 350
km/s.Comment: 4 pages, 3 figures; to appear in "Active Galactic Nuclei, from
Central Engine to Host Galaxy", eds. Collin, Combes & Shlosman, PASP
Conference Series, in pres
MHD Disc Winds and Linewidth Distributions
We study AGN emission line profiles combining an improved version of the
accretion disc-wind model of Murray & Chiang with the magneto-hydrodynamic
model of Emmering et al. We show how the shape, broadening and shift of the C
IV line depend not only on the viewing angle to the object but also on the wind
launching angle, especially for small launching angles. We have compared the
dispersions in our model C IV linewidth distributions to observational upper
limit on that dispersion, considering both smooth and clumpy torus models. As
the torus half-opening angle (measured from the polar axis) increases above
about 18? degrees, increasingly larger wind launching angles are required to
match the observational constraints. Above a half-opening angle of about 47?
degrees, no wind launch angle (within the maximum allowed by the MHD solutions)
can match the observations. Considering a model that replaces the torus by a
warped disc yields the same constraints obtained with the two other models
Conference Summary: AGN Physics with the Sloan Digital Sky Survey
The ``AGN Physics with the Sloan Digital Sky Survey'' conference was held at
Princeton University in July 2003 to bring together groups working inside and
outside of the SDSS collaboration at radio through X-ray wavelengths to discuss
the common goal of better understanding the physics of Active Galactic Nuclei
(AGN). Although we still do not have a full understanding of AGN, much progress
has been made in recent years. In this conference summary, we concentrate on
those topics discussed at the meeting where we believe that there has been
significant change or where there is a new standard of comparison, as well as
on important new trends in AGN research.Comment: 4 pages, no figures; text now fully matches published versio
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