Enhanced strong-lensing model of MACS J0138.0–2155 based on new JWST and VLT/MUSE observations

We present a new parametric strong-lensing analysis of the galaxy cluster MACS J0138.0–2155 at z L = 0.336. This is the first lens cluster known to show two multiply imaged supernova (SN) siblings, SN Requiem and SN Encore at z SNe = 1.949, enabling a new measurement of the Hubble constant value from the measured relative time delays. We exploited Hubble Space Telescope and James Webb Space Telescope multi-band imaging in synergy with new Multi Unit Spectroscopic Explorer follow-up spectroscopy to develop an improved lens mass model. Specifically, we included 84 cluster members (∼60% of which are spectroscopically confirmed) and two perturber galaxies along the line of sight. Our observables consisted of 23 spectroscopically confirmed multiple images from eight background sources, spanning a fairly wide redshift range from 0.767 to 3.420. To accurately characterise the sub-halo mass component, we calibrated the Faber-Jackson scaling relation based on the stellar kinematic measurements of a subset of 14 bright cluster galaxies. We built several lens models by implementing different cluster total mass parametrisations to assess the statistical and systematic uncertainties on the predicted values of the position and magnification of the observed and future multiple images of SN Requiem and SN Encore. Our reference best-fit lens model reproduces the observed positions of the multiple images with a root mean square offset of 0 . ″ 36 and the multiple-image positions of the SNe and their host galaxy with a remarkable mean precision of only 0 . ″ 05. We measure a projected total mass of M (<60 kpc) = 2.89 −0.03 +0.04 × 10 13 M ⊙ , which is consistent with that independently derived from the X-ray analysis of archival data from the Chandra observatory. We also demonstrate the reliability of the new lens model by reconstructing the extended surface-brightness distribution of the multiple images of the host galaxy. The significant discrepancy between the magnification values predicted by our reference model and those from previous studies, which is critical for understanding the intrinsic properties of the two SNe and their host galaxy, further underscores the need to combine cutting-edge observations with a detailed lens modelling.