Strong Lensing Research Articles

Spectroscopic analysis of the strongly lensed SN Encore: Constraints on cosmic evolution of Type Ia supernovae

Abstract Strong gravitational lensing magnifies the light from a background source, allowing us to study these sources in detail. Here, we study the spectra of a z = 1.95 lensed Type Ia supernova SN Encore for its brightest Image A, taken 39 days apart. We infer the spectral age with template matching using the supernova identification (SNID) software and find the spectra to be at 29.0 ±5.0 and 37.4 ±2.8 rest-frame days post maximum respectively, consistent with separation in the observer frame after accounting for time-dilation. Since SNe Ia measure dark energy properties by providing relative distances between low- and high-z SNe, it is important to test for evolution of spectroscopic properties. Comparing the spectra to composite low-z SN Ia spectra, we find strong evidence for similarity between the local sample and SN Encore. The line velocities of common SN Ia spectral lines, Si II 6355 and Ca II NIR triplet are consistent with the distribution for the low-z sample as well as other lensed SNe Ia, e.g. iPTF16geu (z = 0.409)and SN H0pe (z = 1.78). The consistency between the low-z sample and lensed SNe at high-z suggests no obvious cosmic evolution demonstrating their using as high-z distance indicators, though this needs to be confirmed/refuted via a larger sample. We also find that the spectra of SN Encore match the predictions for explosion models very well. With future large samples of lensed SNe Ia e.g. with the Vera C. Rubin Observatory, spectra at such late phases will be important to distinguish between different explosion scenarios.

Survey of Gravitationally lensed Objects in HSC Imaging (SuGOHI) − X. Strong Lens Finding in The HSC-SSP using Convolutional Neural Networks

Abstract We apply a novel model based on convolutional neural networks (CNN) to identify gravitationally-lensed galaxies in multi-band imaging of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) Survey. The trained model is applied to a parent sample of 2 350 061 galaxies selected from the ∼ 800 deg2 Wide area of the HSC-SSP Public Data Release 2. The galaxies in HSC Wide are selected based on stringent pre-selection criteria, such as multiband magnitudes, stellar mass, star formation rate, extendedness limit, photometric redshift range, etc. The trained CNN assigns a score from 0 to 1, with 1 representing lenses and 0 representing non-lenses. Initially, the CNN selects a total of 20 241 cutouts with a score greater than 0.9, but this number is subsequently reduced to 1 522 cutouts after removing definite non-lenses for further visual inspection. We discover 43 grade A (definite) and 269 grade B (probable) strong lens candidates, of which 97 are completely new. In addition, we also discover 880 grade C (possible) lens candidates, 289 of which are known systems in the literature. We identify 143 candidates from the known systems of grade C that had higher confidence in previous searches. Our model can also recover 285 candidate galaxy-scale lenses from the Survey of Gravitationally lensed Objects in HSC Imaging (SuGOHI), where a single foreground galaxy acts as the deflector. Even though group-scale and cluster-scale lens systems are not included in the training, a sample of 32 SuGOHI-c (i.e., group/cluster-scale systems) lens candidates is retrieved. Our discoveries will be useful for ongoing and planned spectroscopic surveys, such as the Subaru Prime Focus Spectrograph project, to measure lens and source redshifts in order to enable detailed lens modelling.

Fractional Einstein–Gauss–Bonnet Scalar Field Cosmology

Our paper introduces a new theoretical framework called the Fractional Einstein–Gauss–Bonnet scalar field cosmology, which has important physical implications. Using fractional calculus to modify the gravitational action integral, we derived a modified Friedmann equation and a modified Klein–Gordon equation. Our research reveals non-trivial solutions associated with exponential potential, exponential couplings to the Gauss–Bonnet term, and a logarithmic scalar field, which are dependent on two cosmological parameters, m and α0=t0H0 and the fractional derivative order μ. By employing linear stability theory, we reveal the phase space structure and analyze the dynamic effects of the Gauss–Bonnet couplings. The scaling behavior at some equilibrium points reveals that the geometric corrections in the coupling to the Gauss–Bonnet scalar can mimic the behavior of the dark sector in modified gravity. Using data from cosmic chronometers, type Ia supernovae, supermassive Black Hole Shadows, and strong gravitational lensing, we estimated the values of m and α0, indicating that the solution is consistent with an accelerated expansion at late times with the values α0=1.38±0.05, m=1.44±0.05, and μ=1.48±0.17 (consistent with Ωm,0=0.311±0.016 and h=0.712±0.007), resulting in an age of the Universe t0=19.0±0.7 [Gyr] at 1σ CL. Ultimately, we obtained late-time accelerating power-law solutions supported by the most recent cosmological data, and we proposed an alternative explanation for the origin of cosmic acceleration other than ΛCDM. Our results generalize and significantly improve previous achievements in the literature, highlighting the practical implications of fractional calculus in cosmology.

Reconciling concentration to virial mass relations

The concentration--virial mass (c-M) relation is a fundamental scaling relation within the standard cold dark matter (Lambda CDM) framework well established in numerical simulations. However, observational constraints of this relation are hampered by the difficulty of characterising the properties of dark matter haloes. Recent comparisons between simulations and observations have suggested a systematic difference of the c-M relation, with higher concentrations in the latter. In this work, we undertake detailed comparisons between simulated galaxies and observations of a sample of strong-lensing galaxies. We explore several factors of the comparison with strong gravitational lensing constraints, including the choice of the generic dark matter density profile, the effect of radial resolution, the reconstruction limits of observed versus simulated mass profiles, and the role of the initial mass function in the derivation of the dark matter parameters. Furthermore, we show the dependence of the c-M relation on reconstruction and model errors through a detailed comparison of real and simulated gravitational lensing systems. An effective reconciliation of simulated and observed c-M relations can be achieved if one considers less strict assumptions on the dark matter profile, for example, by changing the slope of a generic NFW profile or focusing on rather extreme combinations of stellar-to-dark matter distributions. A minor effect is inherent to the applied method: fits to the NFW profile on a less well-constrained inner mass profile yield slightly higher concentrations and lower virial masses.

Image formation near hyperbolic umbilic in strong gravitational lensing

Hyperbolic umbilic (HU) is a point singularity of the gravitational lens equation, giving rise to a ring-shaped image formation made of four highly magnified images, off-centred from the lens centre. Recent observations have revealed new strongly lensed image formations near HU singularities, and many more are expected in ongoing and future observations. Like fold/cusp, image formations near HU also satisfy magnification relation (), i.e., the signed magnification sum of the four images equals zero. Here, we study how deviates from zero as a function of area () covered by the image formation near HU and the distance ( d) of the central maxima image (which is part of the HU image formation) from the lens centre for ideal single- and double-component cluster-scale lenses. For lens ellipticity values ≥0.3, the central maxima image will form sufficiently far from the lens centre ( d≳5″), similar to the observed HU image formations with . We also find that, in some cases, double-component and actual cluster-scale lenses can lead to large cross-sections for HU image formations for sources at z≳5, effectively increasing the chances to observe HU image formation at high redshifts. Finally, we study the time delay distribution in the observed HU image formation, finding that not only are these images highly magnified, but the relative time delay between various pairs of HU characteristic image formation has a typical value of ∼100 days, an order of magnitude smaller than generic five-image formations in cluster lenses, making such image formations optimal targets for time delay cosmography studies.

Revisiting the effect of lens mass models in cosmological applications of strong gravitational lensing

Abstract Strong gravitational lens system catalogues are typically used to constrain a combination of cosmological and empirical power-law lens mass model parameters, often introducing additional empirical parameters and constraints from high resolution imagery. We investigate these lens models using Bayesian methods through a novel alternative that treats spatial curvature via the non-FLRW timescape cosmology. We apply Markov Chain Monte Carlo methods using the catalogue of 161 lens systems of Chen et al. (2019) in order to constrain both lens and cosmological parameters for: (i) the standard ΛCDM model with zero spatial curvature; and (ii) the timescape model. We then generate large mock data sets to further investigate the choice of cosmology on fitting simple power-law lens models. In agreement with previous results, we find that in combination with single isothermal sphere parameters, models with zero FLRW spatial curvature fit better as the free parameter approaches an unphysical empty universe, ΩM0 → 0. By contrast, the timescape cosmology is found to prefer parameter values in which its cosmological parameter, the present void fraction, is driven to fv0 → 0.73 and closely matches values that best fit independent cosmological data sets: supernovae Ia distances and the cosmic microwave background. This conclusion holds for a large range of seed values fv0 ∈ {0.1, 0.9}, and for timescape fits to both timescape and FLRW mocks. Regardless of cosmology, unphysical estimates of the distance ratios given from power-law lens models result in poor goodness of fit. With larger datasets soon available, separation of cosmology and lens models must be addressed.

The cosmic distance duality relation in light of the time-delayed strong gravitational lensing

Abstract The cosmic distance duality relation (DDR), which links the angular diameter distance and the luminosity distance, is a cornerstone in modern cosmology. Any deviation from DDR may indicate new physics beyond the standard cosmological model. In this paper, we use four high-precision time-delayed strong gravitational lensing (SGL) systems provided by the H0LiCOW to test the validity of DDR. To this end, we directly compare the angular diameter distances from these SGL systems and the luminosity distances from the latest Pantheon+ compilation of SNe Ia. In order to reduce the statistical errors arising from redshift matching, the Gaussian process method is applied to reconstruct the distance-redshift relation from the Pantheon+ dataset. We parameterize the possible violation of DDR in three different models. It is found that all results confirm the validity of DDR at 1$\sigma$ confidence level. Additionally, Monte Carlo simulations based on the future LSST survey indicate that the precision of DDR could reach $10^{-2}$ level with 100 SGL systems.

Foreground biases in strong gravitational lensing

Strong gravitational lensing is a competitive tool to probe the dark matter and energy content of the Universe. However, significant uncertainties can arise from the choice of lens model, and in particular the parameterisation of the line of sight. In this work, we consider the consequences of ignoring the contribution of foreground perturbers in lens modelling. We derive the explicit form of the degeneracy between the foreground shear and the ellipticity of a power law lens, which renders the former quantity effectively unmeasurable from strong lensing observables, and biases measurements of the latter by a few percent. Nonetheless, we demonstrate that this degeneracy does not affect measurements of the Einstein radius. Foreground tidal effects are also not expected to bias the slope of the potential, and any biases in this slope should not affect the recovery of the Hubble constant. The foreground convergence term adds an additional uncertainty to the measurement of H 0, and we show that this uncertainty will be on the order of 1% for lensing systems located along random lines of sight. There is evidence to indicate that the probability of strong lensing is higher towards overdense lines of sight, and this could result in a small systematic bias towards overestimations of H 0.

The SLACS strong lens sample, debiased

Strong gravitational lensing observations can provide extremely valuable information on the structure of galaxies, but their interpretation is made difficult by selection effects, which, if not accounted for, introduce a bias between the properties of strong lens galaxies and those of the general population. A rigorous treatment of the strong lensing bias requires, in principle, to fully forward model the lens selection process. However, doing so for existing lens surveys is prohibitively difficult. With this work we propose a practical solution to the problem: using an empirical model to capture the most complex aspects of the lens finding process, and constraining it directly from the data together with the properties of the lens population. We applied this method to real data from the SLACS sample of strong lenses. Assuming a power-law density profile, we recovered the mass distribution of the parent population of galaxies from which the SLACS lenses were drawn. We found that early-type galaxies with a stellar mass of log M*/M⊙ = 11.3 and average size have a median projected mass enclosed within a 5 kpc aperture of log M5/M⊙ = 11.332 ± 0.013, and an average logarithmic density slope of γ = 1.99 ± 0.03. These values are respectively 0.02 dex and 0.1 lower than inferred when ignoring selection effects. According to our model, most of the bias is due to the prioritisation of SLACS follow-up observations based on the measured velocity dispersion. As a result, the strong lensing bias in γ reduces to ∼0.01 when controlling for stellar velocity dispersion.

Measuring Lens Focal Length in Lens Characteristics Experiments through Science Process Skills

Abstract This research aims to measure the focal distance of a lens using practical lens properties. The specifications of this practical tool are made from durable acrylic material, light and easy to use. The lens nature practice equipment consists of a light source in the form of an incandescent lamp, lens path, image capture screen, arrow diaphragm, power supply, strong positive lens (+100), weak positive lens (+50) and negative lens (-50). In this practical, the light source, object, lens and screen are placed parallel. Measurements are carried out through scientific process skills including observation, classification, measurement, prediction, communication and drawing conclusions which begin with observing the image produced by the lens using three different object-to-screen distances, namely 40 cm, 60 cm and 80 cm. In addition to determining the focal distance, experiments with positive lenses produce real, inverted and magnified images. Meanwhile, in a negative lens, the image is virtual and upright. In the positive strong lens experiment, the focal distances measured at distances L = 80 cm, 60 cm, and 40 cm respectively produced average focus values of 10.53 cm, 10.49 cm, and 9.95 cm with values The standard error is 0.123 and the R square value is 0.928, indicating a fairly accurate model. In the weak positive lens experiment, the focal distances measured at distances L = 80 cm, 60 cm, and 40 cm respectively produced average values of 4.42 cm, 4.58 cm, and 4.34 cm with standard values The error is 0.0018 and the R square value is 0.9423, indicating a very precise model. In the negative lens experiment, the focal distances measured at distances L = 80 cm, 60 cm, and 40 cm respectively produced average values of 9.57 cm, 9.47 cm, and 8.95 cm with standard error values of 0.08 and an R square value of 0.967, indicating a very strong model in explaining data variations. This is in accordance with the theory of lens properties, namely that converging lenses generally have the ability to form real images, while diverging lenses often produce virtual images

Determining The Lens Aberations on Positive Lenses Through Science Process Skill

Abstract This research aims to determine aberrations or image distortions in a positive lens using an optics experiment kit for image distortions. The experimental tool consists of a diaphragm, a positive lens, a light source, lens path, an image capture screen, and a flint glass used to reduce lens distortions. The main tool is made of acrylic, which is durable and easy to use. The lens used is a strong positive lens (+100). The diaphragms used vary, including a slit diaphragm with five slits and a four-ring diaphragm. These diaphragms are used to produce image shapes and observe the distortions that occur. The work process refers to the skills of scientific processes such as observation, classification, measurement, prediction, communication, and conclusion, which are implemented in the work instructions for creating aberrations or image distortions by placing the positive lens parallel to the light source and the image capture screen. Then, the distortions that occur are observed, and a flint glass is placed in front of the light source to reduce the distortions that are formed. By observing the resulting image, it can be seen that the distortions that occur on the positive lens and how the flint glass works to reduce these aberrations. This is in line with the theory that aberrations on a positive lens occur due to imperfect light bias, either because of the different refractive index biases from different media in the lens, or because of the lens shape not being ideal. Flint glass is one of the methods used to reduce these aberrations.

A Multiwavelength Approach to Constraining the Merger Properties of ACT-CL J0034.4+0225

ACT-CL J0034.4+0225 is a previously unrecognized merging galaxy cluster at z = 0.38588 ± 0.00068. Our primary evidence is provided by a 21 ks Chandra image that shows two surface brightness peaks separated by ∼49″ (259 kpc) surrounded by an extended cluster gas distribution. Each gas peak contains a brightest cluster galaxy, offset from the gas peak. We collect new South African Large Telescope optical spectra that, when augmented by archival data, yield redshifts for the two BGCs and 58 other cluster members. Archival Giant Metrewave Radio Telescope and MeerKAT data reveal a radio halo that encompasses the X-ray peaks. We provide and compare three X-ray-based mass estimates (5.0 × 1014 M ⊙, 6.4 × 1014 M ⊙, and 8.6 × 1014 M ⊙). The Planck and ACT Sunyaev–Zel’dovich masses are ≈5.8 × 1014 M ⊙. We constrain the merger state and properties by comparing them to an existing suite of N-body/hydrodynamical models using the measured gas peak separation (259 kpc, projected) and radial velocity difference (0–1000 km s−1). This constrains the epoch of the merger to be within ∼100 Myr of first pericenter passage. A strong lensing analysis constrains the mass ratio to be in the range 1:1–1:20, while the cluster morphology prefers values near the equal-mass range.

Multiband Analysis of Strong Gravitationally Lensed Post-blue Nugget Candidates from the Kilo-degree Survey

During the early stages of galaxy evolution, a significant fraction of galaxies undergo a transitional phase between the “blue nugget” systems, which arise from the compaction of large, active star-forming disks, and the “red nuggets,” which are red and passive compact galaxies. These objects are typically only observable with space telescopes, and detailed studies of their size, mass, and stellar population parameters have been conducted on relatively small samples. Strong gravitational lensing can offer a new opportunity to study them in detail, even with ground-based observations. In this study, we present the first six bona fide samples of strongly lensed post-blue nugget (pBN) galaxies, which were discovered in the Kilo Degree Survey. By using the lensing-magnified luminosity from optical and near-infrared bands, we have derived robust structural and stellar population properties of the multiple images of the background sources. The pBN galaxies have very small sizes of R eff < 1.3 kpc, high mass density inside 1 kpc of log(Σ1/M⊙kpc−2)>9.3 , and low specific star formation rates of log(sSFRGyr-1)≲0 , The size–mass and Σ1–mass relations of this sample are consistent with those of the red nuggets, while their sSFR is close to the lower end of compact star-forming blue nugget systems at the same redshift, suggesting a clear evolutionary link between them.

On the implausible physical implications of a claimed lensed neutral hydrogen detection at redshift z = 1.3

Abstract The Square Kilometre Array mid-frequency array will enable high-redshift detections of neutral hydrogen (H i) emission in galaxies, providing important constraints on the evolution of cold gas in galaxies over cosmic time. Strong gravitational lensing will push back the H i emission frontier towards cosmic noon (z ∼ 2), as has been done for all prominent spectral lines in the interstellar medium of galaxies. Chakraborty &amp; Roy (2023, MNRAS, 519, 4074) report a z = 1.3 H i emission detection towards the well-modelled, galaxy-scale gravitational lens, SDSS J0826+5630. We carry out H i source modelling of the system and find that their claimed H i magnification, μHI = 29 ± 6, requires an H i disk radius of ≲ 1.5 kpc, which implies an implausible mean H i surface mass density in excess of ΣHI &amp;gt; 2000 M⊙ pc−2. This is several orders of magnitude above the highest measured peak values (ΣHI ∼ 10 M⊙ pc−2), above which H i is converted into molecular hydrogen. Our re-analysis requires this to be the highest H i mass galaxy known (MHI ∼ 1011 M⊙), as well as strongly lensed, the latter having a typical probability of order 1 in 103 − 4. We conclude that the claimed detection is spurious.

Strong-lensing and kinematic analysis of CASSOWARY 31: Can strong lensing constrain the masses of multi-plane lenses?

We present a mass measurement for the secondary lens along the line of sight (LoS) from the multi-plane strong lens modeling of the group-scale lens CASSOWARY 31 (CSWA 31). The secondary lens at redshift z = 1.49 is a spiral galaxy well aligned along the LoS with the main lens at z = 0.683. Using the MUSE integral-field spectroscopy of this spiral galaxy, we measured its rotation velocities and determined the mass from the gas kinematics. We compared the mass estimation of the secondary lens from the lensing models to the mass measurement from kinematics, finding that the predictions from strong lensing tend to be higher. By introducing an additional lens plane at z = 1.36 for an overdensity known to be present, we find a mass of ≃1010 M⊙ enclosed within 3.3 kpc of the centroid of the spiral galaxy, which approaches the estimate from kinematics. This shows that secondary-lens mass measurements from multiple-plane modeling are affected by systematic uncertainties from the degeneracies between lens planes and the complex LoS structure. Conducting a detailed analysis of the LoS structures is therefore essential to improve the mass measurement of the secondary lens.

Observable strong field effects of extra spacetime dimension in the braneworld black hole

Inspired by the string theory, the braneworld picture introduces extra dimensions beyond the four that may have observable non-trivial effects in short distance (strong field) gravity experiments. A case in point is the Randall–Sundrum braneworld picture that projects the 5d bulk Weyl tensor onto the 3d brane providing a stress tensor in the effective Einstein field equations on the brane. Dadhich, Maartens, Papadopoulos and Rezania (DMPR) derived an exact braneworld black hole solution of the brane vacuum field equations. The solution formally resembles that of Reissner–Nordström but is physically different from it since the ”tidal charge” Υ in the solution is not the electric charge but an imprint from the fifth dimension allowing both signs in the power law modification ±Υ2r2 to the Schwarzschild metric Υ=0. The corresponding black holes are designated as DMPR±. We study here the effect of Υ on strong field lensing observables and compare in the eikonal limit the ring down quasinormal mode (QNM) frequencies of DMPR− with those of DMPR＋ , the two variants of tidal charge modified Schwarzschild black hole (Υ=0). It turns out that the tidal charge can significantly modify the Schwarzschild lensing observables and QNM frequencies. In particular, we find that the Pretorius–Khurana critical exponent γ of circular null orbits in the DMPR− black hole has a lower value than that for the Schwarzschild black hole, which indicates a stronger Lyapunov instability suggesting that the accretion disks of DMPR− black holes would appear brighter. The case of the SgrA* black hole is considered for a possible constraint on Υ from the EHT observation of its shadow size.

A Strong Lensing Model of RCS1 J0224−0002.5

We present the details of a strong lensing model of RCS1 J0224−0002.5, a strong lensing cluster at z = 0.773, based on data from Hubble Space Telescope/WFC3, Advanced Camera for Surveys, and WFC2. Of particular interest in this field is a z = 4.8786 Lyα emitter (LAE), 15″ from the brightest cluster galaxy (BCG) that stretches northwest to west of the BCG in three different images, with a fourth counter-image ∼4″ southeast of the BCG. Using methods consistent with those used in studying five other LAEs in A. Navarre et al., we find that the cluster is best modeled by two cluster-scale dark matter halos aligned nearly perpendicular to each other at the center of the cluster. A z = 2.396 source is also lensed with six images, providing several constraints that were instrumental in producing this model.

Selection functions of strong lens finding neural networks

ABSTRACT We show that convolution neural networks (CNNs) trained to find strong gravitational lens systems are biased towards systems with larger Einstein radii and large concentrated sources. This selection function is key to fully realizing the potential of the large samples of strong gravitational lens systems that will be found in upcoming wide-field surveys. In this paper, we use a CNN and three training data sets to quantify the network selection function and its implication for the many scientific applications of strong gravitational lensing. We use CNNs with similar architecture as is commonly found in the literature. The networks preferentially select systems with larger Einstein radii and larger sources with more concentrated source-light distributions. Increasing the detection significance threshold to 12$\sigma$ from 8$\sigma$ results in 50 per cent of the selected strong lens systems having Einstein radii $\theta _\mathrm{E}$$\ge$ 1.04 arcsec from $\theta _\mathrm{E}$$\ge$ 0.879 arcsec, source radii $R_S$$\ge$ 0.194 arcsec from $R_S$$\ge$ 0.178 arcsec, and source Sérsic indices $n_{\mathrm{Sc}}^{\mathrm{S}}$$\ge$ 2.62 from $n_{\mathrm{Sc}}^{\mathrm{S}}$$\ge$ 2.55. The model trained to find lensed quasars shows a stronger preference for higher lens ellipticities than those trained to find lensed galaxies. The selection function is independent of the slope of the power law of the mass profiles, hence measurements of this quantity will be unaffected. The lens finder selection function reinforces that of the lensing cross-section, and thus we expect our findings to be a general result for all galaxy–galaxy and galaxy–quasar lens finding neural networks.

A targeted search for strongly lensed supernovae with the Las Cumbres Observatory

ABSTRACT Gravitationally lensed supernovae (glSNe) are of interest for time delay cosmology and SN physics. However, glSNe detections are rare, owing to the intrinsic rarity of SN explosions, the necessity of alignment with a foreground lens, and the relatively short window of detectability. We present the Las Cumbres Observatory Lensed Supernova Search, LCOLSS, a targeted survey designed for detecting glSNe in known strong lensing systems. Using cadenced $r^\prime$-band imaging, LCOLSS targeted 114 galaxy–galaxy lensing systems with high expected SN rates, based on estimated star formation rates. No plausible glSN was detected by LCOLSS during our two year observing program. We carry out an analysis here to measure a detection efficiency for these observations. We then perform Monte Carlo simulations using the predicted supernova rates to determine the expected number of glSN detections. The results of the simulation suggest an expected number of detections and 68 per cent Poisson confidence intervals, $N_{\mathrm{ SN}} = 0.20, [0,2.1]$, $N_{\mathrm{ Ia}} = 0.08, [0,2.0]$, $N_{\mathrm{ CC}} = 0.12, [0,2.0]$, for all SNe, Type Ia SNe, and core-collapse (CC) SNe, respectively. These results are broadly consistent with the absence of a detection in our survey. Analysis of the survey strategy can provide insights for future efforts to develop targeted glSN discovery programs, especially considering the large anticipated yields of upcoming surveys.

Automation of finding strong gravitational lenses in the Kilo Degree Survey with U - DenseLens (DenseLens +Segmentation).

In the context of upcoming large-scale surveys like Euclid, the necessity for the automation of strong lens detection is essential. While existing machine learning pipelines heavily rely on the classification probability (P), this study intends to address the importance of integrating additional metrics, such as Information Content (IC) and the number of pixels above the segmentation threshold ([Formula: see text]), to alleviate the false positive rate in unbalanced data-sets. In this work, we introduce a segmentation algorithm (U-Net) as a supplementary step in the established strong gravitational lens identification pipeline (Denselens), which primarily utilizes [Formula: see text] and [Formula: see text] parameters for the detection and ranking. The results demonstrate that the inclusion of segmentation enables significant reduction of false positives by approximately 25per cent in the final sample extracted from DenseLens, without compromising the identification of strong lenses. The main objective of this study is to automate the strong lens detection process by integrating these three metrics. To achieve this, a decision tree-based selection process is introduced, applied to the Kilo Degree Survey (KiDS) data. This process involves rank-ordering based on classification scores ([Formula: see text]), filtering based on Information Content ([Formula: see text]), and segmentation score ([Formula: see text]). Additionally, the study presents 14 newly discovered strong lensing candidates identified by the U-Denselens network using the KiDS DR4 data.