SLSim: a strong lensing population simulation package

Abstract

Gravitational lensing offers unique insights into cosmology by bending light around massive objects. Strong gravitational lensing, in particular, produces magnified and often multiple images of distant sources, crucial for precise cosmological measurements and understanding the distribution of dark matter in the universe. Current studies are limited by the number of strong gravitational lenses. From upcoming cosmological surveys, we anticipate observing a several orders of magnitude increase in the number of lenses, for both static and transient phenomena. However, detecting and analyzing these events from vast surveys like Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) presents significant challenges. To prepare for these challenges, we introduce SLSim, a versatile simulation tool tailored for the Vera C. Rubin Observatory. SLSim integrates advanced astrophysical models with computational efficiency to generate synthetic strong lens populations under realistic observational conditions. SLSim simulates static and variable lensing scenarios, essential for cosmological studies, training and testing lens search and data analysis pipelines. This paper details SLSim,'s design and implementation, emphasizing its modularity and capabilities across various astrophysical regimes. Validation against observational data and existing simulations confirms SLSim's accuracy in reproducing observed lensing phenomena. SLSim is publicly available at https://github.com/LSST-strong-lensing/slsim, and we anticipate continued development and expansion of its capabilities. Users are encouraged to check the repository for updates and to contribute to ongoing community efforts in strong lensing simulations.

Figures (16)

• Figure 1: Illustration of the different modules and classes of SLSim. In the top dotted box, all the classes and modules shown in blue handle individual objects, and these modules and classes interface with each other to produce a single lens. In the second dotted box, the classes shown in orange manage the population of corresponding objects, interfacing both with each other and with the classes involved in individual lens simulations. The blocks shown in green represent the LSST science pipeline module, along with its tasks and output. This module interfaces with the LensPop class and the image simulation module, generating a realistic strong lens image catalog by injecting simulated lenses into the observational data or sky simulations provided by LSST-DESC.
• Figure 2: Lens population of different categories simulated using SLSim . Galaxy-galaxy lens population with elliptical galaxies as deflectors within a 20 $deg^2$ sky area is shown in blue color. Galaxy-galaxy lens population with halo deflectors within a 10 $deg^2$ sky area is shown in purple color. Lensed quasar population within a 500 $deg^2$ sky area is shown in red color. Lensed supernovae population within a 20,000$deg^2$ sky area is shown in green color. In these plots, $\sigma_v$, $\theta_E$, $z_l$, and $m_l$ represent the velocity dispersion, Einstein radius, redshift, and i-band magnitude of the deflector galaxies, respectively, while $z_s$ and $m_s$ denote the redshift and i-band magnitude of the lensed source.
• Figure 3: Redshift distribution of deflectors (red), lensed sources (blue), and unlensed sources (black dotted) in different simulated lens populations. Left panel: Redshift distributions of deflectors, lensed galaxies, and unlensed galaxies in galaxy-galaxy lens population. For these distributions, lensed source galaxies with $i$-band magnitude less than 27 (5 year of coadd image depth) are used. Middle panel: Redshift distribution of deflectors, lensed quasars, and unlensed quasars in the lensed quasar population. For these distributions, quasars with lensed $i$-band magnitude less than 23.3 (single visit magnitude limit) are used. Right panel: Redshift distribution of deflectors, lensed supernovae, and unlensed supernovae in the lensed supernovae population. For these distributions, supernovae with lensed $i$-band magnitude less than 23.3 (single visit magnitude limit) are used.
• Figure 4: Sample of galaxy-galaxy lens images simulated using SLSim image simulation module. These lens sample are the small subset of the lens population simulated within a $1deg^2$ sky area using SLSim . RGB color images are simulated using the r, i, and g band images.
• Figure 5: Examples of cluster lenses simulated using SLSim . These cluster lenses are simulated using DC2 redmapper cluster catalog and injected to DP0 cutout images. RGB color images are simulated using the r, i, and g band images.