Search

Strong gravitational lenses provide unique laboratories for cosmological and astrophysical investigations, but they must first be discovered – a task that can be met with significant contamination by other astrophysical objects and asterisms. Here we review strong lens searches, covering various sources (quasars, galaxies, supernovae, FRBs, GRBs, and GWs), lenses (early- and late-type galaxies, groups, and clusters), datasets (imaging, spectra, and lightcurves), and wavelengths. We first present the physical characteristics of the lens and source populations, highlighting relevant details for constructing targeted searches. Search techniques are described based on the main lensing feature that is required for the technique to work, namely one of: (i) an associated magnification, (ii) multiple spatially-resolved images, (iii) multiple redshifts, or (iv) a non-zero time delay between images. To use the current lens samples for science, and for the design of future searches, we list several selection biases that exist due to these discovery techniques. We conclude by discussing the future of lens searches in upcoming surveys and the new population of lenses that will be discovered. [ABSTRACT FROM AUTHOR]

We present a weak lensing mass map covering ∼124 deg2 of the Canada–France–Hawaii Telescope Stripe 82 Survey (CS82). We study the statistics of rare peaks in the map, including peak abundance, the peak–peak correlation functions and the tangential-shear profiles around peaks. We find that the abundance of peaks detected in CS82 is consistent with predictions from a Λ cold dark matter cosmological model, once noise effects are properly included. The correlation functions of peaks with different signal-to-noise ratio (SNR) are well described by power laws, and there is a clear cross-correlation between the Sloan Digital Sky Survey III/Constant Mass galaxies and high SNR peaks. The tangential-shear profiles around peaks increase with peak SNR. We fit analytical models to the tangential-shear profiles, including a projected singular isothermal sphere (SIS) model and a projected Navarro, Frenk & White (NFW) model, plus a two-halo term. For the high SNR peaks, the SIS model is rejected at ∼3σ. The NFW model plus a two-halo term gives more acceptable fits to the data. Some peaks match the positions of optically detected clusters, while others are relatively dark. Comparing dark and matched peaks, we find a difference in lensing signal of a factor of 2, suggesting that about half of the dark peaks are false detections. [ABSTRACT FROM AUTHOR]

The low-mass end of the stellar initial mass function (IMF) is constrained by focusing on the baryon-dominated central regions of strong lensing galaxies. We study in this Letter the Einstein Cross (Q2237+0305), a barred galaxy whose bulge acts as lens on a background quasar. The positions of the four quasar images constrain the surface mass density on the lens plane, whereas the surface brightness ( H-band HST/NICMOS imaging) along with deep spectroscopy of the lens (VLT/FORS1) allows us to constrain the stellar mass content, for a range of IMFs. We find that a classical single power law (Salpeter IMF) predicts more stellar mass than the observed lensing estimates. This result is confirmed at the 99 per cent confidence level, and is robust to systematic effects due to the choice of population synthesis models, the presence of dust or the complex disc/bulge population mix. Our non-parametric methodology is more robust than kinematic estimates, as we do not need to make any assumptions about the dynamical state of the galaxy or its decomposition into bulge and disc. Over a range of low-mass power-law slopes (with Salpeter being ) we find that at a 90 per cent confidence level, slopes are ruled out. [ABSTRACT FROM AUTHOR]

Abstract: We present the ZEN (z equals nine) survey: a deep, narrow J-band search for proto-galactic Ly α emission at redshifts z ∼9. In the first phase of the survey, dubbed ZEN1, we combine an exceptionally deep image of the Hubble Deep Field South, obtained using a narrow-band filter centred on the wavelength 1.187μm, with existing deep, broad band images covering optical to near infrared wavelengths. Candidate z ∼9 Ly α-emitting galaxies display a significant narrow-band excess relative to the J s-band that are undetected at optical wavelengths. We detect no sources consistent with this criterion to the 90% point source flux limit of the NB image, F NB =3.28×10−18 ergss−1 cm−2. The survey selection function indicates that we have sampled a volume of approximately 340h−3 Mpc3 to a Ly α emission luminosity of 1043 h−2 ergss−1. When compared to the predicted properties of z ∼9 galaxies based upon no evolution of observed z ∼6 Ly α-emitting galaxies, the ‘volume shortfall’ of the current survey, i.e., the volume required to detect this putative population, is a factor of at least 8–10. We also discuss continuing narrow J-band imaging surveys that will reduce the volume shortfall factor to the point where the no-evolution prediction from z ∼6 is probed in a meaningful manner. [Copyright &y& Elsevier]