4,838 research outputs found
Wide-Field Survey of Globular Clusters in M31. II. Kinematics of the Globular Cluster System
We present a kinematic analysis of the globular cluster(GC) system in M31.
Using the photometric and spectroscopic database of 504 GCs, we have
investigated the kinematics of the M31 GC system. We find that the all GC
system shows strong rotation, with rotation amplitude of v_rot~190km/s, and
that a weak rotation persists even for the outermost samples at |Y|>5kpc. The
rotation-corrected velocity dispersion for the GC system is estimated to be
sigma_{p,r}~130km/s, and it increases from sigma_{p,r}~120km/s at |Y|<1kpc to
sigma_{p,r}~150km/s at |Y|>5kpc. These results are very similar to those for
the metal-poor GCs. This shows that there is a dynamically hot halo in M31 that
is rotating but primarily pressure-supported. We have identified 50
"friendless" GCs, and they appear to rotate around the major axis of M31. For
the subsamples of metal-poor and metal-rich GCs, we have found that the
metal-rich GCs are more centrally concentrated than the metal-poor GCs, and
both subsamples show strong rotation. For the subsamples of bright and faint
GCs, it is found that the rotation for the faint GCs is stronger than that for
the bright GCs. We have identified 56 GCs and GC candidates with X-ray
detection. It is found that the majority of X-ray emitting GCs follow the disk
rotation, and that the redder, more metal-rich, and brighter GCs are more
likely to be detected as X-ray emitting GCs. We have derived a rotation curve
of M31 using the GCs at |Y|<0.6kpc. We have estimated the dynamical mass of M31
using `Projected Mass Estimator(PME)' and `Tracer Mass Estimator(TME)'. We
finally discuss the implication of these results and compare the kinematics of
GCs with that of planetary nebulae in M31.Comment: 62 pages, 26 figues, Accepted by Ap
First Principles Study of Zn-Sb Thermoelectrics
We report first principles LDA calculations of the electronic structure and
thermoelectric properties of -ZnSb. The material is found
to be a low carrier density metal with a complex Fermi surface topology and
non-trivial dependence of Hall concentration on band filling. The band
structure is rather covalent, consistent with experimental observations of good
carrier mobility. Calculations of the variation with band filling are used to
extract the doping level (band filling) from the experimental Hall number. At
this band filling, which actually corresponds to 0.1 electrons per 22 atom unit
cell, the calculated thermopower and its temperature dependence are in good
agreement with experiment. The high Seebeck coefficient in a metallic material
is remarkable, and arises in part from the strong energy dependence of the
Fermiology near the experimental band filling. Improved thermoelectric
performance is predicted for lower doping levels which corresponds to higher Zn
concentrations.Comment: 5 pages, 6 figure
Radion effects on the production of an intermediate-mass scalar and Z at LEP II
We have studied the process, where
is the Higgs and/or radion bosons. The implications of the radion effects on
the preliminary ALEPH data are also discussed. The case of the lighter radion
than Higgs boson is disfavored by the ALEPH analyses of the tagged four-jet
data, since the radion predominantly decays into two gluon jets due to the QCD
trace anomaly. If the radion is highly degenerate in mass with the Higgs, the
cross section can be increased more than at one sigma level, with natural scale
of the vacuum expectation value of the radion.Comment: 10 pages, 1 Postscript figure, final version to appear in PR
Galaxy Orbits for Galaxy Clusters in Sloan Digital Sky Survey and 2dF Galaxy Redshift Survey
We present the results of a study for galaxy orbits in galaxy clusters using
a spectroscopic sample of galaxies in Sloan Digital Sky Survey (SDSS) and 2dF
Galaxy Redshift Survey (2dFGRS). We have determined the member galaxies of
Abell clusters covered by these surveys using the galaxies' redshift and
positional data. We have selected 10 clusters using three criteria: the number
of member galaxies is greater than or equal to 40, the spatial coverage is
complete, and X-ray mass profile is available in the literature. We derive the
radial profile of the galaxy number density and velocity dispersion using all,
early-type, and late-type galaxies for each cluster. We have investigated the
galaxy orbits for our sample clusters with constant and variable velocity
anisotropies over the clustercentric distance using Jeans equation. Using all
member galaxies, the galaxy orbits are found to be isotropic within the
uncertainty for most of sample clusters, although it is difficult to conclude
strongly for some clusters due the large errors and the variation as a function
of the clustercentric distance in the calculated velocity anisotropies. We
investigated the orbital difference between early-type and late-type galaxies
for four sample clusters, and found no significant difference between them.Comment: 59 pages, 21 figures. To appear in ApJ. Paper with high resolution
figures are available at http://astro.kias.re.kr/~hshwang/papers/orbit.pd
The Evolution of the Galaxy Stellar Mass Function at z= 4-8: A Steepening Low-mass-end Slope with Increasing Redshift
We present galaxy stellar mass functions (GSMFs) at 4-8 from a
rest-frame ultraviolet (UV) selected sample of 4500 galaxies, found via
photometric redshifts over an area of 280 arcmin in the CANDELS/GOODS
fields and the Hubble Ultra Deep Field. The deepest Spitzer/IRAC data
yet-to-date and the relatively large volume allow us to place a better
constraint at both the low- and high-mass ends of the GSMFs compared to
previous space-based studies from pre-CANDELS observations. Supplemented by a
stacking analysis, we find a linear correlation between the rest-frame UV
absolute magnitude at 1500 \AA\ () and logarithmic stellar mass
() that holds for galaxies with . We
use simulations to validate our method of measuring the slope of the - relation, finding that the bias is minimized with a hybrid
technique combining photometry of individual bright galaxies with stacked
photometry for faint galaxies. The resultant measured slopes do not
significantly evolve over 4-8, while the normalization of the trend
exhibits a weak evolution toward lower masses at higher redshift. We combine
the - distribution with observed rest-frame UV luminosity
functions at each redshift to derive the GSMFs, finding that the low-mass-end
slope becomes steeper with increasing redshift from
at to at
. The inferred stellar mass density, when integrated over
-, increases by a factor of
between and and is in good agreement with the time integral of the
cosmic star formation rate density.Comment: 27 pages, 17 figures, ApJ, in pres
Applications of Fluorescent Quantum Dots for Reproductive Medicine and Disease Detection
Understanding the mechanisms associated with fertility and disease management in animals remains challenging. Continuing advances in nanotechnology provide new tools and alternative approaches for the investigation of these mechanisms. Fluorescent quantum dot nanoparticles, for example, have unique physicochemical properties, which allow for in vivo and in vitro imaging in various areas of life sciences. Traditional quantum dots contain heavy metal semiconductor cores, which have raised concern over their potential for toxicity. The majority of available quantum dots today prevent heavy metal release with additional chemical and polymer layers for safe water solubility. In this chapter, the most widely used quantum dots made of cadmium selenide, which possess great potential for real-time imaging in disease detection and reproductive medicine, are discussed
Topology of amorphous tetrahedral semiconductors on intermediate lengthscales
Using the recently-proposed ``activation-relaxation technique'' for
optimizing complex structures, we develop a structural model appropriate to
a-GaAs which is almost free of odd-membered rings, i.e., wrong bonds, and
possesses an almost perfect coordination of four. The model is found to be
superior to structures obtained from much more computer-intensive tight-binding
or quantum molecular-dynamics simulations. For the elemental system a-Si, where
wrong bonds do not exist, the cost in elastic energy for removing odd-membered
rings is such that the traditional continuous-random network is appropriate.
Our study thus provides, for the first time, direct information on the nature
of intermediate-range topology in amorphous tetrahedral semiconductors.Comment: 4 pages, Latex and 2 postscript figure
On bulk singularities in the random normal matrix model
We extend the method of rescaled Ward identities of Ameur-Kang-Makarov to
study the distribution of eigenvalues close to a bulk singularity, i.e. a point
in the interior of the droplet where the density of the classical equilibrium
measure vanishes. We prove results to the effect that a certain "dominant part"
of the Taylor expansion determines the microscopic properties near a bulk
singularity. A description of the distribution is given in terms of a special
entire function, which depends on the nature of the singularity (a
Mittag-Leffler function in the case of a rotationally symmetric singularity).Comment: This version clarifies on the proof of Theorem
Quantum coherence and interaction-free measurements
We investigate the extent to which ``interaction-free'' measurements perturb
the state of quantum systems. We show that the absence of energy exchange
during the measurement is not a sufficient criterion to preserve that state, as
the quantum system is subject to measurement dependent decoherence. While it is
possible in general to design interaction-free measurement schemes that do
preserve that state, the requirement of quantum coherence preservation rapidly
leads to a very low efficiency. Our results, which have a simple interpretation
in terms of ``which-way'' arguments, open up the way to novel quantum
non-demolition techniques.Comment: 4 pages incl. 2 PostScript figures (.eps), LaTeX using RevTeX,
submitted to Phys. Rev. A (Rapid Comm.
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