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 $\log{M_*} = 11.5$ 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 z∼0.2z \sim 0.2 are well described by the Navarro-Frenk-White profile

We investigate the internal structure of elliptical galaxies at $z\sim 0.2$ 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 $2.08\pm0.03$ and intrinsic scatter $0.13 \pm 0.02$, 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 ($M/L$) model and a stellar $M/L$ gradient model. For the $M/L$ gradient model, we find that most galaxies are consistent with no $M/L$ 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 $z\sim8$ 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 ($m_{AB}=25.8$) $Y_{098}$-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-$\alpha$, H-$\beta$, [OIII] and [OII] emission in the brightest two foreground galaxies (unresolved at the natural seeing of $0.8$ arcsec), placing the pair at $z=1.327$. We can rule out emission lines contributing all of the observed broadband flux in $H_{160}$ band at $70\sigma$, allowing us to exclude the $z\sim8$ 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 $z\sim8$ objects, and we make a marginal detection of a demagnified secondary image in the deepest ($J_{125}$) 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 $\mu=4.3\pm0.2$. The reconstructed source in the best-fitting model is consistent with luminosities and morphologies of $z\sim8$ LBGs in the literature. The lens model yields a group mass of $9.62\pm0.31\times10^{11} M_{\odot}$ and a stellar mass-to-light ratio for the brightest deflector galaxy of $M_{\star}/L_{B}=2.3^{+0.8}_{-0.6} M_{\odot}/L_{\odot}$ within its effective radius. The foreground galaxies' redshifts would make this one of the few strong lensing deflectors discovered at $z>1$.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, $\alpha_{sps}$, 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 $0.5''$, the strong lensing bias in $\alpha_{sps}$ is $10\%$, while that in the central dark matter mass is $5\%$. 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 $H_0$ 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