380 research outputs found
Wavefront shaping of a Bessel light field enhances light sheet microscopy with scattered light
The project was supported by the UK Engineering and Physical Sciences Research Council, RS MacDonald Charitable Trust, SULSA, and the St. Andrews 600th anniversary BRAINS appeal. K. D. is a Royal Society Wolfson Merit Award holder.Light sheet microscopy has seen a resurgence as it facilitates rapid, high contrast, volumetric imaging with minimal sample exposure. Initially developed for imaging scattered light, this application of light sheet microscopy has largely been overlooked but provides an endogenous contrast mechanism which can complement fluorescence imaging and requires very little or no modification to an existing light sheet fluorescence microscope. Fluorescence imaging and scattered light imaging differ in terms of image formation. In the former the detected light is incoherent and weak whereas in the latter the coherence properties of the illumination source, typically a laser, dictate the coherence of detected light, but both are dependent on the quality of the illuminating light sheet. Image formation in both schemes can be understood as the convolution of the light sheet with the specimen distribution. In this paper we explore wavefront shaping for the enhancement of light sheet microscopy with scattered light. We show experimental verification of this result, demonstrating the use of the propagation invariant Bessel beam to extend the field of view of a high resolution scattered light, light sheet microscope and its application to imaging of biological super-cellular structures with sub-cellular resolution. Additionally, complementary scattering and fluorescence imaging is used to characterize the enhancement, and to develop a deeper understanding of the differences of image formation between contrast mechanisms in light sheet microscopy.Publisher PD
Condensation of `composite bosons' in a rotating BEC
We provide evidence for several novel phases in the dilute limit of rotating
BECs. By exact calculation of wavefunctions and energies for small numbers of
particles, we show that the states near integer angular momentum per particle
are best considered condensates of composite entities, involving vortices and
atoms. We are led to this result by explicit comparison with a description
purely in terms of vortices. Several parallels with the fractional quantum Hall
effect emerge, including the presence of the Pfaffian state.Comment: 4 pages, Latex, 3 figure
Gas stripping in galaxy clusters: a new SPH simulation approach
The influence of a time-varying ram pressure on spiral galaxies in clusters
is explored with a new simulation method based on the N-body SPH/tree code
GADGET. We have adapted the code to describe the interaction of two different
gas phases, the diffuse hot intracluster medium (ICM) and the denser and colder
interstellar medium (ISM). Both the ICM and ISM components are introduced as
SPH particles. As a galaxy arrives on a highly radial orbit from outskirts to
cluster center, it crosses the ICM density peak and experiences a time-varying
wind. Depending on the duration and intensity of the ISM-ICM interaction, early
and late type galaxies in galaxy clusters with either a large or small ICM
distribution are found to show different stripping efficiencies, amounts of
reaccretion of the extra-planar ISM, and final masses. We compare the numerical
results with analytical approximations of different complexity and indicate the
limits of the Gunn & Gott simple stripping formula. Our investigations
emphasize the role of the galactic orbital history to the stripping amount. We
discuss the contribution of ram pressure stripping to the origin of the ICM and
its metallicity. We propose gas accumulations like tails, filaments, or ripples
to be responsible for stripping in regions with low overall ICM occurrence.Comment: 18 pages, 23 figures, accepted for publication in A&
Kinetic decoupling of neutralino dark matter
After neutralinos cease annihilating in the early Universe, they may still
scatter elastically from other particles in the primordial plasma. At some
point in time, however, they will eventually stop scattering. We calculate the
cross sections for neutralino elastic scattering from standard-model particles
to determine the time at which this kinetic decoupling occurs. We show that
kinetic decoupling occurs above a temperature MeV. Thereafter,
neutralinos act as collisionless cold dark matter.Comment: Replaced with revised version, new references adde
M Dwarfs in SDSS Stripe 82: Photometric Light Curves and Flare Rate Analysis
We present a flare rate analysis of 50,130 M dwarf light curves in SDSS
Stripe 82. We identified 271 flares using a customized variability index to
search ~2.5 million photometric observations for flux increases in the u- and
g-bands. Every image of a flaring observation was examined by eye and with a
PSF-matching and image subtraction tool to guard against false positives.
Flaring is found to be strongly correlated with the appearance of H-alpha in
emission in the quiet spectrum. Of the 99 flare stars that have spectra, we
classify 8 as relatively inactive. The flaring fraction is found to increase
strongly in stars with redder colors during quiescence, which can be attributed
to the increasing flare visibility and increasing active fraction for redder
stars. The flaring fraction is strongly correlated with |Z| distance such that
most stars that flare are within 300 pc of the Galactic plane. We derive flare
u-band luminosities and find that the most luminous flares occur on the
earlier-type M dwarfs. Our best estimate of the lower limit on the flaring rate
(averaged over Stripe 82) for flares with \Delta u \ge 0.7 magnitudes on stars
with u < 22 is 1.3 flares hour^-1 square degree^-1 but can vary significantly
with the line-of-sight.Comment: 44 pages, 13 figure
Star-forming galaxies in low-redshift clusters: Data and integrated galaxy properties
This paper is a continuation of an ongoing study of the evolutionary
processes affecting cluster galaxies. Both CCD R band and H alpha narrow-band
imaging was used to determine photometric parameters (m_(r), r_(24), H alpha
flux and equivalent width) and derive star formation rates for 227 CGCG
galaxies in 8 low-redshift clusters. The galaxy sample is a subset of CGCG
galaxies in an objective prism survey of cluster galaxies for H alpha emission.
It is found that detection of emission-line galaxies in the OPS is 85%, 70%,
and 50% complete at the mean surface brightness values of 1.25 x 10^(-19), 5.19
x 10^(-20), and 1.76 x 10^(-20) W m^(-2) arcsec^(-2), respectively, measured
within the R band isophote of 24 mag arcsec^(-2) for the galaxy. The CCD data,
together with matched data from a recent H alpha galaxy survey of UGC galaxies
within 3000 km s^(-1), will be used for a comparative study of R band and H
alpha surface photometry between cluster and field spirals.Comment: Accepted for publication in A&A. 11 pages, including 6 figure
Testing Newtonian Gravity with AAOmega: Mass-to-Light Profiles of Four Globular Clusters
Testing Newtonian gravity in the weak-acceleration regime is vital to our
understanding of the nature of the gravitational interaction. It has recently
been claimed that the velocity dispersion profiles of several globular clusters
flatten out at large radii, reminiscent of galaxy rotation curves, even though
globular clusters are thought to contain little or no dark matter. We
investigate this claim, using AAOmega observations of four globular clusters,
namely M22, M30, M53 and M68. M30, one such cluster that has had this claim
made for its velocity dispersion, was included for comparison with previous
studies. We find no statistically significant flattening of the velocity
dispersion at large radii for any of our target clusters and therefore we infer
the observed dynamics do not require that globular clusters are dark matter
dominated, or a modification of gravity. Furthermore, by applying a simple
dynamical model we determine the radial mass-to-light profiles for each
cluster. The isothermal rotations of each cluster are also measured, with M22
exhibiting clear rotation, M68 possible rotation and M30 and M53 lacking any
rotation, within the uncertainties.Comment: 7 pages, 4 figures and two tables. Accepted by MNRA
Efficient Photometric Selection of Quasars from the Sloan Digital Sky Survey: 100,000 z<3 Quasars from Data Release One
We present a catalog of 100,563 unresolved, UV-excess (UVX) quasar candidates
to g=21 from 2099 deg^2 of the Sloan Digital Sky Survey (SDSS) Data Release One
(DR1) imaging data. Existing spectra of 22,737 sources reveals that 22,191
(97.6%) are quasars; accounting for the magnitude dependence of this
efficiency, we estimate that 95,502 (95.0%) of the objects in the catalog are
quasars. Such a high efficiency is unprecedented in broad-band surveys of
quasars. This ``proof-of-concept'' sample is designed to be maximally
efficient, but still has 94.7% completeness to unresolved, g<~19.5, UVX quasars
from the DR1 quasar catalog. This efficient and complete selection is the
result of our application of a probability density type analysis to training
sets that describe the 4-D color distribution of stars and spectroscopically
confirmed quasars in the SDSS. Specifically, we use a non-parametric Bayesian
classification, based on kernel density estimation, to parameterize the color
distribution of astronomical sources -- allowing for fast and robust
classification. We further supplement the catalog by providing photometric
redshifts and matches to FIRST/VLA, ROSAT, and USNO-B sources. Future work
needed to extend the this selection algorithm to larger redshifts, fainter
magnitudes, and resolved sources is discussed. Finally, we examine some science
applications of the catalog, particularly a tentative quasar number counts
distribution covering the largest range in magnitude (14.2<g<21.0) ever made
within the framework of a single quasar survey.Comment: 35 pages, 11 figures (3 color), 2 tables, accepted by ApJS; higher
resolution paper and ASCII version of catalog available at
http://sdss.ncsa.uiuc.edu/qso/nbckde
Secondary infall model and dark matter scaling relations in intermediate redshift early - type galaxies
Scaling relations among dark matter (DM) and stellar quantities are a
valuable tool to constrain formation scenarios and the evolution of galactic
structures. However, most of the DM properties are actually not directly
measured, but derived through model dependent mass mapping procedures. It is
therefore crucial to adopt theoretically and observationally well founded
models. We use here an updated version of the secondary infall model (SIM) to
predict the halo density profile, taking into account the effects of angular
momentum, dissipative friction and baryons collapse. The resulting family of
halo profiles depends on one parameter only, the virial mass, and nicely fits
the projected mass and aperture velocity dispersion of a sample of intermediate
redshift lens galaxies. We derive DM related quantities (namely the column
density and the Newtonian acceleration) and investigate their correlations with
stellar mass, luminosity, effective radius and virial mass.Comment: 15 pages, 3 figures, 2 tables, accepted for publication on MNRA
The Structure of the Sagittarius Stellar Stream as Traced by Blue Horizontal Branch Stars
We use a sample of blue horizontal branch (BHB) stars from the Sloan Digital
Sky Survey Data Release 7 to explore the structure of the tidal tails from the
Sagittarius Dwarf Galaxy. We use a method yielding BHB star candidates with up
to ~70% purity from photometry alone. The resulting sample has a distance
precision of roughly 5% and can probe distances in excess of 100 kpc. Using
this sample, we identify a possible extension to the trailing arm at distances
of 60-80 kpc from the Sun with an estimated significance of at least 3.8 sigma.
Current models predict that a distant `returning' segment of the debris stream
should exist, but place it substantially closer to the Sun where no debris is
observed in our data. Exploiting the distance precision of our tracers, we
estimate the mean line-of-sight thickness of the leading arm to be ~3 kpc, and
show that the two `bifurcated' branches of the debris stream differ by only 1-2
kpc in distance. With a spectroscopic very pure BHB star subsample, we estimate
the velocity dispersion in the leading arm, 37 km s^-1, which is in reasonable
agreement with models of Sgr disruption. We finally present a sample of
high-probability Sgr BHB stars in the leading arm of Sgr, selected to have
distances and velocities consistent with Sgr membership, to allow further
study.Comment: Astrophysical Journal, in press. 17 pages, 15 figure
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