Cosmography with the Double Source Plane Strong Gravitational Lens AGEL150745+052256

Abstract

Strong gravitational lenses with two background sources at widely separated redshifts are a powerful and independent probe of cosmological parameters. We can use these systems, known as Double-Source-Plane Lenses (DSPLs), to measure the ratio (${\hat{I}}^2$) of angular-diameter distances of the sources, which is sensitive to the matter density ($\hat{I}{\text{c◯}}_m$) 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 ${\hat{I}}^2$. 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 HST/WFC3 imaging and Keck/KCWI spectroscopy. The spectroscopic redshifts for the deflector and two sources in AGEL1507 are $z_{\mathrm{defl}}=0.594$, $z_{S1}=2.163$, and $z_{S2}=2.591$. We measure a stellar velocity dispersion of $\ddot{I}{ƒ}_{\mathrm{obs}}=109\pm 27$ km s${}^{-1}$ for the nearer source. Using $\ddot{I}{ƒ}_{\mathrm{obs}}$ for the main deflector (from literature) and S1, we test the robustness of our DSPL model. We measure ${\hat{I}}^2=0.953_{-0.010}^{+0.008}$ for AGEL1507 and infer $\hat{I}{\text{c◯}}_{\mathrm{m}}=0.33_{-0.23}^{+0.38}$ for $\hat{I}›$CDM cosmology. Combining AGEL1507 with the published model of the Jackpot lens improves the precision on $\hat{I}{\text{c◯}}_{\mathrm{m}}$ ($\hat{I}›$CDM) and w (wCDM) by $\sim 10\%$. The inclusion of DSPLs significantly improves the constraints when combined with Plancks cosmic microwave background observations, enhancing precision on w by $30\%$. This paper demonstrates the 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.

19 pages, 10 figures, Submitted for publication to the Astrophysical Journal (ApJ)