628 research outputs found
Constraints on the Inner Mass Profiles of Lensing Galaxies from Missing Odd Images
Most gravitational lens systems consist of two or four observable images. The
absence of detectable odd images allows us to place a lower limit on the
power-law slope of the inner mass profile of lensing galaxies. Using a sample
of six two-image radio-loud lens systems and assuming a singular power-law
surface density (Sigma proportional to r^{-beta}) for the inner several kpc of
the mass distribution, we find that there is less than a 10% probability that
the data are consistent with profile slopes beta < 0.80. Furthermore,
individual mass modeling yields beta > 0.85 for B0739+366 and beta > 0.91 for
B1030+074. Modeling central black holes as additional point masses changes the
constraints in these systems to beta > 0.84 and beta > 0.83, respectively. The
inner mass profiles of lensing galaxies are therefore not much shallower than
isothermal.Comment: Final published version, minor typos corrected, 13 page
Galaxy-Scale Strong Lensing Tests of Gravity and Geometric Cosmology: Constraints and Systematic Limitations
Galaxy-scale strong gravitational lenses with measured stellar velocity
dispersions allow a test of the weak-field metric on kiloparsec scales and a
geometric measurement of the cosmological distance-redshift relation, provided
that the mass-dynamical structure of the lensing galaxies can be independently
constrained to a sufficient degree. We combine data on 53 galaxy-scale strong
lenses from the Sloan Lens ACS Survey with a well-motivated fiducial set of
lens-galaxy parameters to find (1) a constraint on the post-Newtonian parameter
gamma = 1.01 +/- 0.05 and (2) a determination of Omega_Lambda = 0.75 +/- 0.17
under the assumption of a flat universe. These constraints assume that the
underlying observations and priors are free of systematic error. We evaluate
the sensitivity of these results to systematic uncertainties in (1) total
mass-profile shape, (2) velocity anisotropy, (3) light-profile shape, and (4)
stellar velocity dispersion. Based on these sensitivities, we conclude that
while such strong-lens samples can in principle provide an important tool for
testing general relativity and cosmology, they are unlikely to yield precision
measurements of gamma and Omega_Lambda unless the properties of the lensing
galaxies are independently constrained with substantially greater accuracy than
at present.Comment: 8 pages, 5 figures; Accepted to Ap
Zitterbewegung of relativistic electrons in a magnetic field and its simulation by trapped ions
One-electron 3+1 and 2+1 Dirac equations are used to calculate the motion of
a relativistic electron in a vacuum in the presence of an external magnetic
field. First, calculations are carried on an operator level and exact
analytical results are obtained for the electron trajectories which contain
both intraband frequency components, identified as the cyclotron motion, as
well as interband frequency components, identified as the trembling motion
(Zitterbewegung, ZB). Next, time-dependent Heisenberg operators are used for
the same problem to compute average values of electron position and velocity
employing Gaussian wave packets. It is shown that the presence of a magnetic
field and the resulting quantization of the energy spectrum has pronounced
effects on the electron Zitterbewegung: it introduces intraband frequency
components into the motion, influences all the frequencies and makes the motion
stationary (not decaying in time) in case of the 2+1 Dirac equation. Finally,
simulations of the 2+1 Dirac equation and the resulting electron ZB in the
presence of a magnetic field are proposed and described employing trapped ions
and laser excitations. Using simulation parameters achieved in recent
experiments of Gerritsma and coworkers we show that the effects of the
simulated magnetic field on ZB are considerable and can certainly be observed.Comment: 19 pages, 9 figures, published versio
Plant responses to simulated carbon capture and storage (CCS) CO2 pipeline leakage: the effect of soil type
Carbon capture and storage (CCS) has been proposed as a bridging technology to enable the transition to an energy system based on renewable sources. Many high CO2?emitting industries (such as the power industry) are distant from potential carbon storage sites (such as offshore geological reservoirs) and an infrastructure of CO2 transportation must therefore be developed to carry the CO2 to safe storage. As such there is a need to understand the risks involved and the mitigation of potential leaks associated with CCS and dense?phase CO2 transportation networks. Since 2012 a number of experimental studies have provided a mechanistic understanding of the risks posed to crops as a function of CO2 leakage from CCS infrastructure. However, what remains largely unresolved is the role played by both soil type and soil structure in mitigating and / or enhancing plant stresses. In this study we provide an experimental framework to evaluate these effects. Wheat and beetroot were grown in four different experimental soils to test the effects of specific soil attributes (organic, low pH; organic, open structure; organic, limed; loam, neutral pH) on crop performance when exposed to high levels (?40%) of CO2 in the soil environment. Comparison between treatment and controls and across the soil types reveals little difference in terms of biomass or plant stress chemistry. From a stakeholder perspective these findings suggest that soil type may play only a minor role in mitigating or amplifying plant stress in response to the unlikely event of a CO2 leak from CCS infrastructure
CFHT AO Imaging of the CLASS Gravitational Lens System B1359+154
We present adaptive optics imaging of the CLASS gravitational lens system
B1359+154 obtained with the Canada-France-Hawaii Telescope (CFHT) in the
infrared K band. The observations show at least three brightness peaks within
the ring of lensed images, which we identify as emission from multiple lensing
galaxies. The results confirm the suspected compound nature of the lens, as
deduced from preliminary mass modeling. The detection of several additional
nearby galaxies suggests that B1359+154 is lensed by the compact core of a
small galaxy group. We attempted to produce an updated lens model based on the
CFHT observations and new 5-GHz radio data obtained with the MERLIN array, but
there are too few constraints to construct a realistic model at this time. The
uncertainties inherent with modeling compound lenses make B1359+154 a
challenging target for Hubble constant determination through the measurement of
differential time delays. However, time delays will offer additional
constraints to help pin down the mass model. This lens system therefore
presents a unique opportunity to directly measure the mass distribution of a
galaxy group at intermediate redshift.Comment: 12 pages including 3 figures; ApJL accepte
The Sloan Lens ACS Survey. IX. Colors, Lensing and Stellar Masses of Early-type Galaxies
We present the current photometric dataset for the Sloan Lens ACS (SLACS)
Survey, including HST photometry from ACS, WFPC2, and NICMOS. These data have
enabled the confirmation of an additional 15 grade `A' (certain) lens systems,
bringing the number of SLACS grade `A' lenses to 85; including 13 grade `B'
(likely) systems, SLACS has identified nearly 100 lenses and lens candidates.
Approximately 80% of the grade `A' systems have elliptical morphologies while
~10% show spiral structure; the remaining lenses have lenticular morphologies.
Spectroscopic redshifts for the lens and source are available for every system,
making SLACS the largest homogeneous dataset of galaxy-scale lenses to date. We
have developed a novel Bayesian stellar population analysis code to determine
robust stellar masses with accurate error estimates. We apply this code to
deep, high-resolution HST imaging and determine stellar masses with typical
statistical errors of 0.1 dex; we find that these stellar masses are unbiased
compared to estimates obtained using SDSS photometry, provided that informative
priors are used. The stellar masses range from 10^10.5 to 10^11.8 M and
the typical stellar mass fraction within the Einstein radius is 0.4, assuming a
Chabrier IMF. The ensemble properties of the SLACS lens galaxies, e.g. stellar
masses and projected ellipticities, appear to be indistinguishable from other
SDSS galaxies with similar stellar velocity dispersions. This further supports
that SLACS lenses are representative of the overall population of massive
early-type galaxies with M* >~ 10^11 M, and are therefore an ideal
dataset to investigate the kpc-scale distribution of luminous and dark matter
in galaxies out to z ~ 0.5.Comment: 20 pages, 18 figures, 5 tables, published in Ap
Golden gravitational lensing systems from the Sloan Lens ACS Survey. I. SDSS J1538+5817: one lens for two sources
We present a lensing and photometric study of the exceptional system SDSS
J1538+5817, identified by the SLACS survey. The lens is a luminous elliptical
at redshift z=0.143. Using HST public images in two different filters, the
presence of two background sources lensed into an Einstein ring and a double
system is ascertained. Our new spectroscopic observations, performed at the
NOT, reveal that the two sources are located at the same redshift z=0.531. We
investigate the total mass distribution of the lens between 1 and 4 kpc from
the galaxy center by means of parametric and non-parametric lensing codes that
describe the multiple images as point-like objects. Several disparate lensing
models agree on: (1) reproducing accurately the observed image positions; (2)
predicting a nearly axisymmetric total mass distribution, centered and oriented
as the light distribution; (3) measuring a value of 8.11 x 10^{10} M_{Sun} for
the total mass projected within the Einstein radius of 2.5 kpc; (4) estimating
a total mass density profile slightly steeper than an isothermal one. A fit of
the SDSS multicolor photometry with CSP models provides a value of 20 x 10^{10}
M_{Sun} for the total stellar mass of the galaxy and of 0.9 for the fraction of
projected luminous over total mass enclosed inside the Einstein radius. By
combining lensing and photometric mass measurements, we differentiate the lens
mass content in terms of luminous and dark matter components. This
two-component modeling, which is viable only in extraordinary systems like SDSS
J1538+5817, leads to a description of the global properties of the galaxy dark
matter halo. Extending these results to a larger number of lenses would improve
considerably our understanding of galaxy formation and evolution processes in
the LCDM scenario.Comment: 21 pages, 16 figures, accepted by The Astrophysical Journa
Redshifts of CLASS Radio Sources
Spectroscopic observations of a sample of 42 flat-spectrum radio sources from
the Cosmic Lens All-Sky Survey (CLASS) have yielded a mean redshift of with an RMS spread of 0.95, at a completeness level of 64%. The sample
consists of sources with a 5-GHz flux density of 25-50 mJy, making it the
faintest flat-spectrum radio sample for which the redshift distribution has
been studied. The spectra, obtained with the Willam Herschel Telescope (WHT),
consist mainly of broad-line quasars at and narrow-line galaxies at
. Though the mean redshift of flat-spectrum radio sources exhibits
little variation over more than two orders of magnitude in radio flux density,
there is evidence for a decreasing fraction of quasars at weaker flux levels.
In this paper we present the results of our spectroscopic observations, and
discuss the implications for constraining cosmological parameters with
statistical analyses of the CLASS survey.Comment: 10 pages, AJ accepte
Cyclotron motion in graphene
We investigate cyclotron motion in graphene monolayers considering both the
full quantum dynamics and its semiclassical limit reached at high carrier
energies. Effects of zitterbewegung due to the two dispersion branches of the
spectrum dominate the irregular quantum motion at low energies and are obtained
as a systematic correction to the semiclassical case. Recent experiments are
shown to operate in the semiclassical regime.Comment: 6 pages, 1 figure include
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