Spectroscopic and X-ray Modeling of the Strong Lensing Galaxy Cluster MACS J0138.0-2155

We model the total mass and galactic substructure in the strong lensing galaxy cluster MACS J0138.0-2155 using a combination of Chandra X-ray data, Multi-Unit Spectroscopic Explorer (MUSE) spectroscopy, and Hubble Space Telescope imaging. MACS J0138.0-2155 lenses a source galaxy at \(z=1.95\) which hosts two strongly lensed supernovae, Requiem and Encore. We find MACS J0138.0-2155 to have an X-ray temperature of \(6.7\pm0.4\) keV and a velocity dispersion of cluster member galaxies of \(718^{+132}_{-182}\) km s\(^{-1}\). These lead to the mass estimates for the cluster of \(M_{500} = 5.2^{+1.5}_{-1.2} \times 10^{14} M_\odot\) from the X-ray results and \(M_{200} \approx 3.6^{+2.0}_{-2.7} \times 10 ^{14} M_{\odot}\) from the velocity dispersion results. The round morphology of the X-ray emission indicates that this cluster is relaxed with an ellipticity within the lensing region of \(e=0.12\pm0.03\). Using 18 of the brightest, non-blended, quiescent galaxies, we fit the cluster specific Faber-Jackson relation, including a set of 81 variations in the analysis choices to estimate the systematic uncertainties in our results. We find a slope of \(\alpha = 0.26 \pm 0.06 (\mathrm{stat.}) \pm 0.03 (\mathrm{sys.})\) with an intrinsic scatter of \(\Delta \sigma = 31^{+8}_{-6} (\mathrm{stat.}) \pm 4 (\mathrm{sys.})\) km s\(^{-1}\) at a reference velocity dispersion of \(\sim 220\) km s\(^{-1}\). We also report on significant galaxies along the line-of-sight potentially impacting the lens modeling, including a massive galaxy with stellar velocity dispersion of \(236 \pm 3\) km s\(^{-1}\) which lies close in projection to the central cluster galaxy. This galaxy is part of a small group at a slightly higher redshift than the cluster.