1,129 research outputs found
Color Gradients in Early-Type Galaxies in Clusters at the Redshift from 0.37 to 0.56
Color gradients in elliptical galaxies in distant clusters ()
are examined by using the archival deep imaging data of Wide Field Planetary
Camera 2 (WFPC2) on-board the Hubble Space Telescope (HST). Obtained color
gradients are compared with the two model gradients to examine the origin of
the color gradients. In one model, a color gradient is assumed to be caused by
a metallicity gradient of stellar populations, while in the other one, it is
caused by an age gradient. Both of these model color gradients reproduce the
average color gradient seen in nearby ellipticals, but predict significantly
different gradients at a redshift larger than 0.3. Comparison between the
observed gradients and the model gradients reveals that the metallicity
gradient is much more favorable as the primary origin of color gradients in
elliptical galaxies in clusters. The same conclusion has been obtained for
field ellipticals by using those at the redshift from 0.1 to 1.0 in the Hubble
Deep Field-North by Tamura et al. (2000). Thus, it is also suggested that the
primary origin of the color gradients in elliptical galaxies does not depend on
galaxy environment.Comment: 23 pages LaTeX, 5 PostScript figures, accepted for publication in The
Astronomical Journa
Using error correction to determine the noise model
Quantum error correcting codes have been shown to have the ability of making
quantum information resilient against noise. Here we show that we can use
quantum error correcting codes as diagnostics to characterise noise. The
experiment is based on a three-bit quantum error correcting code carried out on
a three-qubit nuclear magnetic resonance (NMR) quantum information processor.
Utilizing both engineered and natural noise, the degree of correlations present
in the noise affecting a two-qubit subsystem was determined. We measured a
correlation factor of c=0.5+/-0.2 using the error correction protocol, and
c=0.3+/-0.2 using a standard NMR technique based on coherence pathway
selection. Although the error correction method demands precise control, the
results demonstrate that the required precision is achievable in the
liquid-state NMR setting.Comment: 10 pages, 3 figures. Added discussion section, improved figure
A Look At Three Different Scenarios for Bulge Formation
In this paper, we present three qualitatively different scenarios for bulge
formation: a secular evolution model in which bulges form after disks and
undergo several central starbursts, a primordial collapse model in which bulges
and disks form simultaneously, and an early bulge formation model in which
bulges form prior to disks. We normalize our models to the local z=0
observations of de Jong & van der Kruit (1994) and Peletier & Balcells (1996)
and make comparisons with high redshift observations. We consider model
predictions relating directly to bulge-to-disk properties. As expected, smaller
bulge-to-disk ratios and bluer bulge colors are predicted by the secular
evolution model at all redshifts, although uncertainties in the data are
currently too large to differentiate strongly between the models.Comment: 19 pages, 6 figures, accepted for publication in the Astrophysical
Journa
The Age of Cluster Galaxies from Continuum Colors
We determine the age of 1,104 early-type galaxies in eight rich clusters ( to ) using a new continuum color technique. We find that
galaxies in clusters divide into two populations, an old population with a mean
age similar to the age of the Universe (12 Gyrs) and a younger population with
a mean age of 9 Gyrs. The older population follows the expected relations for
mass and metallicity that imply a classic monolithic collapse origin. Although
total galaxy metallicity is correlated with galaxy mass, it is uncorrelated
with age. It is impossible, with the current data, to distinguish between a
later epoch of star formation, longer duration of star formation or late bursts
of star formation to explain the difference between the old and young
populations. However, the global properties of this younger population are
correlated with cluster environmental factors, which implies secondary
processes, post-formation epoch, operate on the internal stellar population of
a significant fraction of cluster galaxies. In addition, the mean age of the
oldest galaxies in a cluster are correlated with cluster velocity dispersion
implying that galaxy formation in massive clusters begins at earlier epochs
than less massive clusters.Comment: 35 pages, 10 figures, accepted by Ap
Numerical Analyses of Weakly Nonlinear Velocity-Density Coupling
We study evolution of various statistical quantities of smoothed cosmic
density and velocity fields using N-body simulations. The parameter
characterizes nonlinear coupling of
these two fields and determines behavior of bulk velocity dispersion as a
function of local density contrast.
It is found that this parameter depends strongly on the smoothing scale even
in quasi-linear regimes where the skewness parameter
is nearly constant and close to the predicted value by the second-order
perturbation theory. We also analyze weakly nonlinear effects caused by an
adaptive smoothing known as the gather approach.Comment: 22 pages, 4 figures, to appear in ApJ (558, Sep 10
The Angular Three-Point Correlation Function in the Quasilinear Regime
We calculate the normalized angular three-point correlation function (3PCF),
, as well as the normalized angular skewness, , assuming the
small-angle approximation, for a biased mass distribution in flat and open
cold-dark-matter (CDM) models with Gaussian initial conditions. The
leading-order perturbative results incorporate the explicit dependence on the
cosmological parameters, the shape of the CDM transfer function, the linear
evolution of the power spectrum, the form of redshift distribution function,
and linear and nonlinear biasing, which may be evolving. Results are presented
for different redshift distributions, including that appropriate for the APM
Galaxy Survey, as well as for a survey with a mean redshift of (such as the VLA FIRST Survey). Qualitatively, many of the results found for
and are similar to those obtained in a related treatment of the
spatial skewness and 3PCF (Buchalter & Kamionkowski 1999), such as a
leading-order correction to the standard result for in the case of
nonlinear bias (as defined for unsmoothed density fields), and the sensitivity
of the configuration dependence of to both cosmological and biasing models.
We show that since angular CFs are sensitive to clustering over a range of
redshifts, the various evolutionary dependences included in our predictions
imply that measurements of in a deep survey might better discriminate
between models with different histories, such as evolving vs. non-evolving
bias, that can have similar spatial CFs at low redshift. Our calculations
employ a derived equation---valid for open, closed, and flat models---for
obtaining the angular bispectrum from the spatial bispectrum in the small-angle
approximation.Comment: 45 pages, including 11 Figures, submitted to the Astrophysical
Journa
The Canada-UK Deep Submillimeter Survey VI: The 3-Hour Field
We present the complete submillimeter data for the Canada-UK Deep
Submillimeter Survey (CUDSS) 3-hour field. The obeservations were taken with
the Submillimeter Common-User Bolometer Array (SCUBA) on the James Clerk
Maxwell Telescope on Mauna Kea. The 3-hour field is one of two main fields in
our survey and covers 60 square arcminutes to a 3-sigma depth of 3 mJy. In this
field we have detected 27 sources above 3-sigma and 15 above 3.5-sigma. We
assume the source counts follow the form and
measure = 3.3. This is in good agreement with previous
studies and further supports our claim (Eales et al., 2000) that SCUBA sources
brighter than 3 mJy produce ~20% of the 850m background energy. Using
preliminary ISO 15 m maps and VLA 1.4 GHz data we have identified
counterparts for six objects and have marginal detections at 450m for two
additional sources. With this information we estimate a median redshift for the
sample of 2.00.5, with 10% lying at 1. We have measured the
angular clustering of S850 > 3 mJy sources using the source catalogues from the
CUDSS two main fields, the 3-hour and 14-hour fields, and find a marginal
detection of clustering, primarily from the 14-hour field, of
. This is consistent with clustering at
least as strong as that seen for the Lyman-break galaxy population and the
Extremely Red Objects. Since SCUBA sources are selected over a broader range in
redshifts than these two populations the strength of the true spatial
clustering is expected to be correspondingly stronger.Comment: 17 pages, 8 figures, submitted to Ap
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