JWST Bullet Cluster redshifts and spectra

We modelled the cluster with the parametric lens modelling code Lenstool. We incorporated several large-scale halos, cluster member galaxies, intracluster gas, and group-scale halos surrounding the cluster core, motivated by spectroscopic studies of cluster member kinematics. We describe the main cluster component with a complex, elongated double-peaked distribution, along with the subcluster, modelled using a single large-scale halo coinciding closely with the brightest cluster galaxy at a projected separation of 4_-2_^+3^kpc.

The uncertainty of the displacement has been improved three-fold thanks to the addition of JWST systems. The addition of group-scale substructures, roughly following the two axes of cluster assembly, improves the fit to the multiple image positions and provides a physically motivated alternative to a constant shear component. Our lens model shows the closest agreement with previous studies in aperture mass profiles at ~60kpc from the brightest cluster galaxies (BCGs), but exhibits significant differences in the detailed mass distribution as a result of different lens-modelling strategies and adopted constraints.

The differences are reflected in small, but spatially coherent deviations between the new spectroscopic redshifts and redshifts predicted by earlier lens models.