3,400 research outputs found
Transport of Indirect Excitons in a Potential Energy Gradient
We realized a potential energy gradient - a ramp - for indirect excitons
using a shaped electrode at constant voltage. We studied transport of indirect
excitons along the ramp and observed that the exciton transport distance
increases with increasing density and temperature.Comment: 4 pages, 3 figure
The Case for Optically-Thick High Velocity Broad Line Region Gas in Active Galactic Nuclei
A combined analysis of the profiles of the main broad quasar emission lines
in both Hubble Space Telescope and optical spectra shows that while the
profiles of the strong UV lines are quite similar, there is frequently a strong
increase in the Ly-alpha/H-alpha ratio in the high-velocity gas. We show that
the suggestion that the high velocity gas is optically-thin presents many
problems. We show that the relative strengths of the high velocity wings arise
naturally in an optically-thick BLR component. An optically-thick model
successfully explains the equivalent widths of the lines, the Ly-alpha/H-alpha
ratios and flatter Balmer decrements in the line wings, the strengths of CIII]
and the lambda 1400 blend, and the strong variability of high-velocity,
high-ionization lines (especially HeII and HeI).Comment: 34 pages in AASTeX, including 10 pages of figures. Submitted to
Astrophysical Journa
The UV Properties of the Narrow Line Quasar I Zwicky 1
I Zw 1 is the prototype narrow line quasar. We report here the results of our
study of the UV emission of I Zw 1 using a high S/N (50-120) spectrum obtained
with the HST FOS. The following main new results are obtained: 1. The Mg II and
Al III doublets are partially/fully resolved. The measured doublet ratios
verify theoretical predictions that the lines are thermalized in the BLR. 2. A
weak associated UV absorption system is detected in N~V, and possibly also in C
IV and Lya, suggesting an outflow with a velocity of 1870 km/s and velocity
dispersion <300 km/s. 3. Lines from ions of increasing ionization level show
increasing excess blue wing flux, and an increasing line peak velocity shift,
reaching a maximum blueshift of about 2000 km/s for He II 1640. This may
indicate an out-flowing component in the BLR, where the ionization level
increases with velocity, and which is visible only in the approaching
direction. The highest velocity part of this outflow may produce the associated
UV absorption system. 4. The small C III] 1909 EW, and the small C III]
1909/Lya and C III] 1909/Si III] 1892 flux ratios indicate a typical BLR
density of 10^11, i.e. about an order of magnitude larger than implied by C
III] 1909 in most quasars. A BLR component of a higher density is implied by
the EW and doublet ratio of the Al III 1857 doublet. 5. Prominent Fe II UV 191
emission is seen, together with weaker line emission at 1294 and 1871 A. These
three features have been proposed as evidence for significant Lya pumping of
the 8-10 eV levels of Fe II. 6. Significant Fe III emission is present. The Fe
III UV 34 and UV 48 multiplets are clearly resolved, and Fe III UV 1, UV 47, UV
50, and UV 68 may also be present. (Shortened version)Comment: 28 pages, 1 table and 7 figures included. Uses aas2pp4.sty. Scheduled
for the Astrophysical Journal November 10, 1997 issue, Vol. 48
Black Hole Mass Estimates of Radio Selected Quasars
The black hole (BH) mass in the centre of AGN has been estimated for a sample
of radio-selected flat-spectrum quasars to investigate the relationship between
BH mass and radio properties of quasars. We have used the virial assumption
with measurements of the H FWHM and luminosity to estimate the central
BH mass. In contrast to previous studies we find no correlation between BH mass
and radio power in these AGN. We find a range in BH mass similar to that seen
in radio-quiet quasars from previous studies. We believe the reason that the
low BH mass radio-loud quasars have not been measured in previous studies is
due to optical selection effects which tend to miss the less optically luminous
radio-loud sources.Comment: 22 pages, 7 figures, accepted for publication in Ap
Discovery of a Jet-Like Structure at the High Redshift QSO CXOMP J084128.3+131107
The Chandra Multiwavelength Project (ChaMP) has discovered a jet-like
structure associated with a newly recognized QSO at redshift z=1.866. The
system was 9.4 arcmin off-axis during an observation of 3C 207. Although
significantly distorted by the mirror PSF, we use both a raytrace and a nearby
bright point source to show that the X-ray image must arise from some
combination of point and extended sources, or else from a minimum of three
distinct point sources. We favor the former situation, as three unrelated
sources would have a small probability of occurring by chance in such a close
alignment. We show that interpretation as a jet emitting X-rays via inverse
Compton (IC) scattering on the cosmic microwave background (CMB) is plausible.
This would be a surprising and unique discovery of a radio-quiet QSO with an
X-ray jet, since we have obtained upper limits of 100 microJy on the QSO
emission at 8.46 GHz, and limits of 200 microJy for emission from the putative
jet.Comment: 12 pages including 4 figures. Accepted for publication by ApJ Letter
An Empirical Ultraviolet Template for Iron Emission in Quasars as Derived from I Zw 1
We present an empirical template spectrum suitable for fitting/subtracting
and studying the FeII and FeIII line emission in the restframe UV spectra of
active galatic nuclei (AGNs), the first empirical UV iron template to cover the
full 1250 - 3090 A range. Iron emission is often a severe contaminant in
optical--UV spectra of AGNs. Its presence complicates and limits the accuracy
of measurements of both strong and weak emission lines and the continuum
emission, affecting studies of line and continuum interrelations, the
ionization structure, and elemental abundances in AGNs. Despite the wealth of
work on modeling the AGN FeII emission and the need to account for it in
observed AGN spectra, there is no UV template electronically available to aid
this process. The iron template we present is based on HST spectra of the
Narrow Line Seyfert 1, IZw1. Its intrinsic narrow lines (~900 km/s) and rich
iron spectrum make the template particularly suitable for use with most AGN
spectra. The iron emission spectrum and the line identifications and
measurements are presented and compared with the work of Laor et al. We
illustrate the application of the derived FeII and FeIII templates by fitting
and subtracting the iron emission from UV spectra of four high-z quasars and of
the nearby quasar, 3C273. We briefly discuss the small discrepancies between
this observed iron emission and the UV template, and compare the template with
previously published ones. We discuss the advantages and limitations of the
templates and of the template fitting method. We conclude that the templates
work sufficiently well to be a valuable and important tool for eliminating and
studying the iron emission in AGNs, at least until accurate theoretical iron
emission models are developed. (Abridged)Comment: 73 pages including 7 figures, 6 tables. To appear in ApJS. Preprint
is also available at
http://www.astronomy.ohio-state.edu/~vester/IronEmission
Electrostatic Conveyer for Excitons
We report on the study of indirect excitons in moving lattices - conveyers
created by a set of AC voltages applied to the electrodes on the sample
surface. The wavelength of this moving lattice is set by the electrode
periodicity, the amplitude is controlled by the applied voltage, and the
velocity is controlled by the AC frequency. We observed the dynamical
localization-delocalization transition for excitons in the conveyers and
measured its dependence on the exciton density and conveyer amplitude and
velocity. We considered a model for exciton transport via conveyers. The
theoretical simulations are in agreement with the experimental data.Comment: 4 pages, 4 figures + supplemental material including two video
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