649 research outputs found
RingFinder: automated detection of galaxy-scale gravitational lenses in ground-based multi-filter imaging data
We present RingFinder, a tool for finding galaxy-scale strong gravitational
lenses in multiband imaging data. By construction, the method is sensitive to
configurations involving a massive foreground early-type galaxy and a faint,
background, blue source. RingFinder detects the presence of blue residuals
embedded in an otherwise smooth red light distribution by difference imaging in
two bands. The method is automated for efficient application to current and
future surveys, having originally been designed for the 150-deg2 Canada France
Hawaii Telescope Legacy Survey (CFHTLS). We describe each of the steps of
RingFinder. We then carry out extensive simulations to assess completeness and
purity. For sources with magnification mu>4, RingFinder reaches 42% (resp. 25%)
completeness and 29% (resp. 86%) purity before (resp. after) visual inspection.
The completeness of RingFinder is substantially improved in the particular
range of Einstein radii 0.8 < REin < 2. and lensed images brighter than g =
22.5, where it can be as high as 70%. RingFinder does not introduce any
significant bias in the source or deflector population. We conclude by
presenting the final catalog of RingFinder CFHTLS galaxy-scale strong lens
candidates. Additional information obtained with Hubble Space Telescope and
Keck Adaptive Optics high resolution imaging, and with Keck and Very Large
Telescope spectroscopy, is used to assess the validity of our classification,
and measure the redshift of the foreground and the background objects. From an
initial sample of 640,000 early type galaxies, RingFinder returns 2500
candidates, which we further reduce by visual inspection to 330 candidates. We
confirm 33 new gravitational lenses from the main sample of candidates, plus an
additional 16 systems taken from earlier versions of RingFinder. First
applications are presented in the SL2S galaxy-scale Lens Sample paper series.Comment: 32 pages (aastex 2col format), 6 figs, ApJ Accepte
The SL2S Galaxy-scale Lens Sample. III. Lens Models, Surface Photometry and Stellar Masses for the final sample
We present Hubble Space Telescope (HST) imaging data and CFHT Near IR
ground-based images for the final sample of 56 candidate galaxy-scale lenses
uncovered in the CFHT Legacy Survey as part of the Strong Lensing in the Legacy
Survey (SL2S) project. The new images are used to perform lens modeling,
measure surface photometry, and estimate stellar masses of the deflector
early-type galaxies. Lens modeling is performed on the HST images (or CFHT when
HST is not available) by fitting the spatially extended light distribution of
the lensed features assuming a singular isothermal ellipsoid mass profile and
by reconstructing the intrinsic source light distribution on a pixelized grid.
Based on the analysis of systematic uncertainties and comparison with inference
based on different methods we estimate that our Einstein Radii are accurate to
\sim3%. HST imaging provides a much higher success rate in confirming
gravitational lenses and measuring their Einstein radii than CFHT imaging does.
Lens modeling with ground-based images however, when successful, yields
Einstein radius measurements that are competitive with spaced-based images.
Information from the lens models is used together with spectroscopic
information from the companion paper IV to classify the systems, resulting in a
final sample of 39 confirmed (grade-A) lenses and 17 promising candidates. The
redshifts of the main deflector span a range 0.3<zd< 0.8, providing an
excellent sample for the study of the cosmic evolution of the mass distribution
of early-type galaxies over the second half of the history of the Universe.Comment: Submitted to The Astrophysical Journa
The SL2S Galaxy-scale Lens Sample. V. Dark Matter Halos and Stellar IMF of Massive Early-type Galaxies out to Redshift 0.8
We investigate the cosmic evolution of the internal structure of massive
early-type galaxies over half of the age of the Universe. We perform a joint
lensing and stellar dynamics analysis of a sample of 81 strong lenses from the
SL2S and SLACS surveys and combine the results with a hierarchical Bayesian
inference method to measure the distribution of dark matter mass and stellar
IMF across the population of massive early-type galaxies. Lensing selection
effects are taken into account. We find that the dark matter mass projected
within the inner 5 kpc increases for increasing redshift, decreases for
increasing stellar mass density, but is roughly constant along the evolutionary
tracks of early-type galaxies. The average dark matter slope is consistent with
that of an NFW profile, but is not well constrained. The stellar IMF
normalization is close to a Salpeter IMF at and scales
strongly with increasing stellar mass. No dependence of the IMF on redshift or
stellar mass density is detected. The anti-correlation between dark matter mass
and stellar mass density supports the idea of mergers being more frequent in
more massive dark matter halos.Comment: Accepted for publication on The Astrophysical Journal. Revised
version. (25 pages, 18 figures
The SL2S Galaxy-scale Lens Sample. IV. The dependence of the total mass density profile of early-type galaxies on redshift, stellar mass, and size
We present optical and near infrared spectroscopy obtained at Keck, VLT, and
Gemini for a sample of 36 secure strong gravitational lens systems and 17
candidates identified as part of the SL2S survey. The deflectors are massive
early-type galaxies in the redshift range z_d=0.2-0.8, while the lensed sources
are at z_s=1-3.5. We combine this data with photometric and lensing
measurements presented in the companion paper III and with lenses from the
SLACS and LSD surveys to investigate the cosmic evolution of the internal
structure of massive early-type galaxies over half the age of the universe. We
study the dependence of the slope of the total mass density profile \gamma'
(\rho(r)\propto r^{-\gamma'}) on stellar mass, size, and redshift. We find that
two parameters are sufficent to determine \gamma' with less than 6% residual
scatter. At fixed redshift, \gamma' depends solely on the surface stellar mass
density \partial \gamma'/ \partial \Sigma_*=0.38\pm 0.07, i.e. galaxies with
denser stars also have steeper slopes. At fixed M_* and R_{eff}, \gamma'
depends on redshift, in the sense that galaxies at a lower redshift have
steeper slopes (\partial \gamma' / \partial z = -0.31\pm 0.10). However, the
mean redshift evolution of \gamma' for an individual galaxy is consistent with
zero d\gamma'/dz=-0.10\pm0.12. This result is obtained by combining our
measured dependencies of \gamma' on z,M_*,R_{eff} with the evolution of the
R_{eff}-M_* taken from the literature, and is broadly consistent with current
models of the formation and evolution of massive early-type galaxies. Detailed
quantitative comparisons of our results with theory will provide qualitatively
new information on the detailed physical processes at work.Comment: Submitted to The Astrophysical Journa
Dark matter halos of massive elliptical galaxies at are well described by the Navarro-Frenk-White profile
We investigate the internal structure of elliptical galaxies at
from a joint lensing-dynamics analysis. We model Hubble Space Telescope images
of a sample of 23 galaxy-galaxy lenses selected from the Sloan Lens ACS (SLACS)
survey. Whereas the original SLACS analysis estimated the logarithmic slopes by
combining the kinematics with the imaging data, we estimate the logarithmic
slopes only from the imaging data. We find that the distribution of the
lensing-only logarithmic slopes has a median and intrinsic
scatter , consistent with the original SLACS analysis. We
combine the lensing constraints with the stellar kinematics and weak lensing
measurements, and constrain the amount of adiabatic contraction in the dark
matter (DM) halos. We find that the DM halos are well described by a standard
Navarro-Frenk-White halo with no contraction on average for both of a constant
stellar mass-to-light ratio () model and a stellar gradient model.
For the gradient model, we find that most galaxies are consistent with no
gradient. Comparison of our inferred stellar masses with those obtained
from the stellar population synthesis method supports a heavy initial mass
function (IMF) such as the Salpeter IMF. We discuss our results in the context
of previous observations and simulations, and argue that our result is
consistent with a scenario in which active galactic nucleus feedback
counteracts the baryonic-cooling-driven contraction in the DM halos.Comment: 26 pages, 19 figures, 3 tables. This version: accepted to MNRA
A spectroscopically confirmed z=1.327 galaxy-scale deflector magnifying a z~8 Lyman-Break galaxy in the Brightest of Reionizing Galaxies survey
We present a detailed analysis of an individual case of gravitational lensing
of a Lyman-Break galaxy (LBG) in a blank field, identified in Hubble
Space Telescope imaging obtained as part of the Brightest of Reionizing
Galaxies survey. To investigate the close proximity of the bright
() -dropout to a small group of foreground galaxies, we
obtained deep spectroscopy of the dropout and two foreground galaxies using
VLT/X-Shooter. We detect H-, H-, [OIII] and [OII] emission in
the brightest two foreground galaxies (unresolved at the natural seeing of
arcsec), placing the pair at . We can rule out emission lines
contributing all of the observed broadband flux in band at
, allowing us to exclude the candidate as a low redshift
interloper with broadband photometry dominated by strong emission lines. The
foreground galaxy pair lies at the peak of the luminosity, redshift and
separation distributions for deflectors of strongly lensed objects,
and we make a marginal detection of a demagnified secondary image in the
deepest () filter. We show that the configuration can be accurately
modelled by a singular isothermal ellipsoidal deflector and a S\'{e}rsic source
magnified by a factor of . The reconstructed source in the
best-fitting model is consistent with luminosities and morphologies of
LBGs in the literature. The lens model yields a group mass of
and a stellar mass-to-light ratio for the
brightest deflector galaxy of within its effective radius. The foreground galaxies'
redshifts would make this one of the few strong lensing deflectors discovered
at .Comment: Accepted for publication in MNRAS. 16 pages, 11 figures, 3 table
An Experiment on Innovation and Collusion
This paper examines the relationship between product innovation and the success of price collusion using novel laboratory experiments. Average market prices in low innovation (LO) experiments are significantly higher than those in high innovation, but otherwise identical experiments. This price difference is attributed to LO experimental subjects\u27 greater common market experience. The data illustrate how collusion can be perceived as the only way to make it in LO markets where product innovation is not a viable strategy for increasing profits. They suggest that product homogeneity can be a proximate cause, and product innovation an ultimate cause, of collusion
Purification and characterization of ubiquitin-associated and free thiol protease inhibitors from dormant Artemia embryos.
Encysted embryos of the brine shrimp Artemia contain a mixture of thiol protease inhibitors (TPI\u27s) which appear to be important in the regulation of a cathepsin B-like protease. These TPI\u27s were subjected to gel filtration, anion exchange chromatography, two types of cation exchange procedures (fast protein liquid chromatography and CM-cellulose chromatography) and high performance liquid chromatography (HPLC). Cation exchange chromatography of inhibitor preparations on a Mono S column fractionated six TPI peaks. Using HPLC to purify the proteins the TPI\u27s eluted between 39% and 41% acetonitrile from a C-18 column revealing considerable hydrophobicity of each inhibitor. SDS-urea PAGE of these protease inhibitors yielded a mixture of proteins with approximate molecular weights of 4.9 and 12.3 kDa. Amino acid sequence analysis of the major protein peak showed it to be identical to human ubiquitin (4.9 kDa). It appears that extracts from dormant Artemia embryos contain a mixture of free and ubiquitin-associated low molecular weight TPI\u27s; ubiquitin may be involved in the conformational modification of TPI\u27s in dormant Artemia embryos. (Abstract shortened by UMI.)Dept. of Biological Sciences. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1990 .S677. Source: Masters Abstracts International, Volume: 30-03, page: 0748. Thesis (M.Sc.)--University of Windsor (Canada), 1990
Scanning Tunneling Microscopy and Fabrication of Nanometer Scale Structures at the Liquid-Gold Interface
The Scanning Tunneling Microscope (STM) can image gold surfaces covered with a variety of liquids. This paper reviews the results obtained using the STM to image gold surfaces covered with liquid. These results include the creation of 10 nm structures, images of the electrochemical process of electroplating, and the production of atomically flat Au (111) surfaces. We conclude that in the future STM will find further application in the area of nanostructure fabrication and electrochemistry. The trend in the field is toward greater control of the electrochemical environment
Strong lensing selection effects
Context. Strong lenses are a biased subset of the general population of
galaxies.
Aims. The goal of this work is to quantify how lens galaxies and lensed
sources differ from their parent distribution, namely the strong lensing bias.
Methods. We first studied how the strong lensing cross-section varies as a
function of lens and source properties. Then, we simulated strong lensing
surveys with data similar to that expected for Euclid and measured the strong
lensing bias in different scenarios. We focused particularly on two quantities:
the stellar population synthesis mismatch parameter, , defined as
the ratio between the true stellar mass of a galaxy and the stellar mass
obtained from photometry, and the central dark matter mass at fixed stellar
mass and size.
Results. Strong lens galaxies are biased towards larger stellar masses,
smaller half-mass radii and larger dark matter masses. The amplitude of the
bias depends on the intrinsic scatter in the mass-related parameters of the
galaxy population and on the completeness in Einstein radius of the lens
sample. For values of the scatter that are consistent with observed scaling
relations and a minimum detectable Einstein radius of , the strong
lensing bias in is , while that in the central dark matter
mass is . The bias has little dependence on the properties of the source
population: samples of galaxy-galaxy lenses and galaxy-quasar lenses that probe
the same Einstein radius distribution are biased in a very similar way.
Conclusions. Given current uncertainties, strong lensing observations can be
used directly to improve our current knowledge of the inner structure of
galaxies, without the need to correct for selection effects. Time-delay
measurements of from lensed quasars can take advantage of prior
information obtained from galaxy-galaxy lenses with similar Einstein radii.Comment: Published on Astronomy & Astrophysics. A two-minute summary video of
this paper is available at https://youtu.be/UmS9jRHTmZ
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