Cosmography with the double-source-plane strong gravitational lens AGEL150745+052256

Strong gravitational lenses with two background sources at widely separated redshifts are a promising independent probe of cosmological parameters. We can use these systems, known as double-source-plane lenses (DSPLs), to measure the ratio (β) of angular-diameter distances of the sources, which is sensitive to the matter density (Ω_m) and the equation-of-state parameter for dark-energy (w). However, DSPLs are rare and require high-resolution imaging and spectroscopy for detection, lens modeling, and measuring β. Here, we report only the second DSPL ever used to measure cosmological parameters. We model the DSPL AGEL150745+052256 from the ASTRO 3D Galaxy Evolution with Lenses (AGEL) survey using Hubble Space Telescope/Wide-Field Camera 3 imaging and Keck Cosmic Web Imager spectroscopy. The spectroscopic redshifts for the deflector and two sources in AGEL1507 are z_defl = 0.594, z_S1 = 2.163, and z_S2 = 2.591. We measure a stellar velocity dispersion of σ_obs = 109 ± 27 km s⁻¹ for the nearer source (S1). Using σ_obs for the main deflector (from literature) and S1, we test the robustness of our DSPL model. We measure β = 0.95 3 − 0.010 + 0.008 for AGEL1507 and infer Ω_m = 0.3 3 − 0.23 + 0.38 for ΛCDM cosmology. Combining AGEL1507 with the published model of the Jackpot lens improves the precision on Ω_m (ΛCDM) and w (wCDM) by ∼10%. The inclusion of DSPLs significantly improves the constraints when combined with Planck’s cosmic microwave background observations, enhancing the precision on w by 30%. This paper demonstrates the potential constraining power of DSPLs and their complementarity to other standard cosmological probes. Tighter future constraints from larger DSPL samples discovered from ongoing and forthcoming large-area sky surveys would provide insights into the nature of dark energy.