8,056 research outputs found
A STIS Survey for OVI Absorption Systems at 0.12 < z < 0.5 I.: The Statistical Properties of Ionized Gas
We have conducted a systematic survey for intervening OVI absorbers in
available echelle spectra of 16 QSOs at z_QSO = 0.17-0.57. These spectra were
obtained using HST/STIS with the E140M grating. Our search uncovered a total of
27 foreground OVI absorbers with rest-frame absorption equivalent width
W_r(1031) > 25mA. Ten of these QSOs exhibit strong OVI absorbers in their
vicinity. Our OVI survey does not require the known presence of Lya, and the
echelle resolution allows us to identify the OVI absorption doublet based on
their common line centroid and known flux ratio. We estimate the total redshift
survey path, \Delta z, using a series of Monte-Carlo simulations, and find that
\Delta z=1.66, 2.18, and 2.42 for absorbers of strength W_r = 30, 50 and 80mA,
respectively, leading to a number density of dN(W > 50mA)/dz = 6.7 +/- 1.7 and
dN(W > 30mA)/dz = 10.4 +/- 2.2. In contrast, we also measure dN/dz = 27 +/- 9
for OVI absorbers of W_r > 50mA at |\Delta v|< 5000 kms from the background
QSOs. Using the random sample of OVI absorbers with well characterized survey
completeness, we estimate a mean cosmological mass density of the OVI gas
\Omega(OVI)h = 1.7 +/- 0.3 x 10^-7. In addition, we show that <5% of OVI
absorbers originate in underdense regions that do not show a significant trace
of HI. Furthermore, we show that the neutral gas column N(HI) associated with
these OVI absorbers spans nearly five orders of magnitude, and show moderate
correlation with N(OVI). Finally, while the number density of OVI absorbers
varies substantially from one sightline to another, it also appears to be
inversely correlated with the number density of HI absorbers along individual
lines of sight.Comment: 12 pages. ApJ accepte
Efficient orthogonal control of tunnel couplings in a quantum dot array
Electrostatically-defined semiconductor quantum dot arrays offer a promising
platform for quantum computation and quantum simulation. However, crosstalk of
gate voltages to dot potentials and inter-dot tunnel couplings complicates the
tuning of the device parameters. To date, crosstalk to the dot potentials is
routinely and efficiently compensated using so-called virtual gates, which are
specific linear combinations of physical gate voltages. However, due to
exponential dependence of tunnel couplings on gate voltages, crosstalk to the
tunnel barriers is currently compensated through a slow iterative process. In
this work, we show that the crosstalk on tunnel barriers can be efficiently
characterized and compensated for, using the fact that the same exponential
dependence applies to all gates. We demonstrate efficient calibration of
crosstalk in a quadruple quantum dot array and define a set of virtual barrier
gates, with which we show orthogonal control of all inter-dot tunnel couplings.
Our method marks a key step forward in the scalability of the tuning process of
large-scale quantum dot arrays.Comment: 8 pages, 7 figure
Photometry and Photometric Redshifts of Faint Galaxies in the Hubble Deep Field South NICMOS Field
We present a catalog of photometry and photometric redshifts of 335 faint
objects in the HDF-S NICMOS field. The analysis is based on (1) infrared images
obtained with the Hubble Space Telescope (HST) using the Near Infrared Camera
and Multi-Object Spectrograph (NICMOS) with the F110W, F160W, and F222M
filters, (2) an optical image obtained with HST using the Space Telescope
Imaging Spectrograph (STIS) with no filter, and (3) optical images obtained
with the European Southern Observatory (ESO) Very Large Telescope (VLT) with U,
B, V, R, and I filters. The primary utility of the catalog of photometric
redshifts is as a survey of faint galaxies detected in the NICMOS F160W and
F222M images. The sensitivity of the survey varies significantly with position,
reaching a limiting depth of AB(16,000) ~ 28.7 and covering 1.01 arcmin^2 to
AB(16,000) = 27 and 1.05 arcmin^2 to AB(16,000) = 26.5. The catalog of
photometric redshifts identifies 21 galaxies (or 6% of the total) of redshift z
> 5, 8 galaxies (or 2% of the total) of redshift z > 10, and 11 galaxies (or 3%
of the total) of best-fit spectral type E/S0, of which 5 galaxies (or 1% of the
total) are of redshift z > 1.Comment: 33 pages, 10 figures, accepted for publication in the Astrophysical
Journal, August 1, 2000 issu
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