Impact of an external galaxy group beyond the analysis aperture

Determine whether incorporating the effect of the galaxy group outside the 120-arcsecond analysis aperture, for example by increasing the maximum radius used in the weighted number-count analysis, changes the estimated external convergence for RXJ1131-1231.

Background

The RXJ1131-1231 external-convergence estimate differs from the fiducial value reported by Suyu et al. (2013), although the estimate obtained without using the modelled external shear is consistent with the result presented in this work. The earlier use of the shear constraint was partly motivated by a group of galaxies located outside the 120-arcsecond aperture employed in the analysis and aligned with the direction of the modelled external shear.

The unresolved issue is whether that group contributes sufficiently to the line-of-sight mass distribution to affect the inferred convergence. The paper suggests testing this by expanding the maximum radius, r_max, of the environmental analysis.

References

The inclusion of this shear constraint for that system in was in part motivated by the presence of a group of galaxies outside the 120'' aperture used in the analysis, but in the direction of the modelled external shear. While we avoid the use of this shear for the reasons discussed in \cref{sec:external_shear}, it nonetheless remains to be tested whether incorporating the effect of this group, for example by increasing $r_\mathrm{max}$, impacts the estimated convergence.

— TDCOSMO XXXI: New techniques in line-of-sight studies of time delay lenses  (2609.11652 - Johnson et al., 10 Sep 2026) in Section 4.4, “Comparison to the literature”