432 research outputs found
Combining weak and strong lensing in cluster potential reconstruction
We propose a method for recovering the two-dimensional gravitational
potential of galaxy clusters which combines data from weak and strong
gravitational lensing. A first estimate of the potential from weak lensing is
improved at the approximate locations of critical curves. The method can be
fully linearised and does not rely on the existence and identification of
multiple images. We use simulations to show that it recovers the surface-mass
density profiles and distributions very accurately, even if critical curves are
only partially known and if their location is realistically uncertain. We
further describe how arcs at different redshifts can be combined, and how
deviations from weak lensing can be included.Comment: 9 pages, 5 figures, A&A in press, changes to match the accepted
versio
Using VLBI Data to Investigate the Galaxy Structure in the Gravitationally Lensed System B1422+231
Gravitationally lensed systems with multiply imaged quasars are an excellent tool for studying the properties of distant galaxies. In particular, they provide the most accurate mass measures for the lensing galaxy. The system B1422+231 is a well studied example of a quadruply imaged quasar, with high-quality VLBI data available. Very accurate data on image positions, fluxes and deconvolved image sizes provide good constraints for lensing models. We discuss here the failure of smooth models in fitting the data. Since it is intuitively clear that the mass of a lens galaxy is not a smooth entity, we have investigated how deviation from a smooth model can influence lensing phenomena, especially the image flux ratios. To explore expectations about the level of substructure in galaxies and its influence on strong lensing, N-body simulations of a model galaxy are employed. By using the mass distribution of this model galaxy as a lens, synthetic data sets of different four image system configurations are generated. Their analysis can possibly provide evidence for the presence and strong influence of substructure in the primary lens galaxy
Asymmetric Gravitational Lenses in TeVeS and Application to the Bullet Cluster
Aims: We explore the lensing properties of asymmetric matter density
distributions in Bekenstein's Tensor-Vector-Scalar theory (TeVeS). Methods:
Using an iterative Fourier-based solver for the resulting non-linear scalar
field equation, we numerically calculate the total gravitational potential and
derive the corresponding TeVeS lensing maps. Results: Considering variations on
rather small scales, we show that the lensing properties significantly depend
on the lens's extent along the line of sight. Furthermore, all simulated TeVeS
convergence maps strongly track the dominant baryonic components, non-linear
effects, being capable of counteracting this trend, turn out to be very small.
Setting up a toy model for the cluster merger 1E0657-558, we infer that TeVeS
cannot explain observations without assuming an additional dark mass component
in both cluster centers, which is in accordance with previous work.Comment: LaTex, 14 pages, 10 figures, references added, 2 figures removed,
minor text changes to fit accepted version (A&A
Spherically symmetric ADM gravity with variable G and Lambda(c)
This paper investigates the Arnowitt--Deser--Misner (hereafter ADM) form of
spherically symmetric gravity with variable Newton parameter G and cosmological
term Lambda(c). The Newton parameter is here treated as a dynamical variable,
rather than being merely an external parameter as in previous work on closely
related topics. The resulting Hamilton equations are obtained; interestingly, a
static solution exists, that reduces to Schwarzschild geometry in the limit of
constant G, describing a Newton parameter ruled by a nonlinear differential
equation in the radial variable r. A remarkable limiting case is the one for
which the Newton parameter obeys an almost linear growth law at large r. An
exact solution for G as a function of r is also obtained in the case of
vanishing cosmological constant. Some observational implications of these
solutions are obtained and briefly discussed.Comment: 16 pages, 2 figures. The presentation has been improved in all
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Effects of microstructure and growth conditions on quantum emitters in gallium nitride
Single-photon emitters in gallium nitride (GaN) are gaining interest as attractive quantum systems due to the well-established techniques for growth and nanofabrication of the host material, as well as its remarkable chemical stability and optoelectronic properties. We investigate the nature of such single- photon emitters in GaN with a systematic analysis of various samples produced under different growth conditions. We explore the effect that intrinsic structural defects (dislocations and stacking faults), doping and crystal orientation in GaN have on the formation of quantum emitters. We investigate the relationship between the position of the emitters—determined via spectroscopy and photoluminescence measurements—and the location of threading dislocations—characterised both via atomic force microscopy and cathodoluminescence. We find that quantum emitters do not correlate with stacking faults or dislocations; instead, they are more likely to originate from point defects or impurities whose density is modulated by the local extended defect density
Addressing a single NV spin with a macroscopic dielectric microwave cavity
We present a technique for addressing single NV center spins in diamond
over macroscopic distances using a tunable dielectric microwave cavity. We
demonstrate optically detected magnetic resonance (ODMR) for a single NV
center in a nanodiamond (ND) located directly under the macroscopic microwave
cavity. By moving the cavity relative to the ND, we record the ODMR signal as a
function of position, mapping out the distribution of the cavity magnetic field
along one axis. In addition, we argue that our system could be used to
determine the orientation of the NV major axis in a straightforward
manner
Engineering and Tuning of Quantum Emitters in Few-Layer Hexagonal Boron Nitride
© 2019 American Chemical Society. Quantum technologies require robust and photostable single photon emitters (SPEs). Hexagonal boron nitride (hBN) has recently emerged as a promising candidate to host bright and optically stable SPEs operating at room temperature. However, the emission wavelength of the fluorescent defects in hBN has, to date, been shown to be uncontrolled, with a widespread of zero phonon line (ZPL) energies spanning a broad spectral range (hundreds of nanometers), which hinders the potential development of hBN-based devices and applications. Here we demonstrate chemical vapor deposition growth of large-area, few-layer hBN films that host large quantities of SPEs: -100-200 per 10 × 10 μm 2 . More than 85% of the emitters have a ZPL at (580 ± 10) nm, a distribution that is an order of magnitude narrower than reported previously. Furthermore, we demonstrate tuning of the ZPL wavelength using ionic liquid devices over a spectral range of up to 15 nm-the largest obtained to date from any solid-state SPE. The fabricated devices illustrate the potential of hBN for the development of hybrid quantum nanophotonic and optoelectronic devices based on two-dimensional materials
The Grism Lens-Amplified Survey from Space (GLASS). IX. The dual origin of low-mass cluster galaxies as revealed by new structural analyses
Using deep Hubble Frontier Fields imaging and slitless spectroscopy from the
Grism Lens-Amplified Survey from Space, we analyze 2200 cluster and 1748 field
galaxies at to determine the impact of environment on galaxy
size and structure at , an unprecedented limit at these
redshifts. Based on simple assumptions--we find no significant
differences in half-light radii () between equal-mass cluster or field
systems. More complex analyses-)-reveal local density
) to induce only a ( confidence) reduction in
beyond what can be accounted for by color, Sersic index (), and
redshift () effects.Almost any size difference between galaxies in high- and
low-density regions is thus attributable to their different distributions in
properties other than environment. Indeed, we find a clear color-
correlation in low-mass passive cluster galaxies () such
that bluer systems have larger radii, with the bluest having sizes consistent
with equal-mass star-forming galaxies. We take this as evidence that
large- low-mass passive cluster galaxies are recently acquired systems
that have been environmentally quenched without significant structural
transformation (e.g., by ram pressure stripping or starvation).Conversely,
of small- low-mass passive cluster galaxies appear to have been
in place since . Given the consistency of the small- galaxies'
stellar surface densities (and even colors) with those of systems more than ten
times as massive, our findings suggest that clusters mark places where galaxy
evolution is accelerated for an ancient base population spanning most masses,
with late-time additions quenched by environment-specific mechanisms are mainly
restricted to the lowest masses.Comment: The accepted version. The catalog is available through the GLASS web
page (http://glass.astro.ucla.edu), or
https://www.astr.tohoku.ac.jp/~mtakahiro/Publication/Morishita17
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