tokens: ones (Figure 8 ). Overall, Figure 11 does not suggest any significant trends in the mass error with respect to merger history, percentage of incomplete data, or percentage of unbound particles. Thus, except in extreme cases, these quantities may not play a role in underestimating the mass. In the following section, we explore the possibility that the inner GC analogs are influencing the model fit, as suggested in Section 5.1.3 . 5.3. Sensitivity to Inner Tracers Our studies of the MW, and in particular the sensitivity analyses in Papers 2 and 3 , found an increased mass estimate when inner GCs were not included in the analysis. We repeat this kind of analysis here by removing the inner GC analogs from the MUGS2 galaxies, and recalculating the mass estimate M 200 . Each galaxy in the MUGS2 simulation is unique in shape and spatial distribution of GC analogs. In order to remove inner GC analogs in a consistent way across all galaxies, we find the scale radius r s of each galactic disk via a simple exponential fit, and then remove GC analogs within 7.5 r s . The MW’s scale radius is roughly 2 kpc, so in our own Galaxy this cut is akin to removing GCs within r gc = 15 kpc of the Galactic center. It should be noted that the galaxies already had GC analogs removed within 3 r s in the original analysis. The new mass estimates after removing the inner GC analogs are shown in Figure 12 . In general, the estimates are better but at the cost of wider Bayesian c.r. The true M 200 values lie within the Bayesian c.r. in 13 out of 18 cases—a slight improvement from 8 out of 18 (Figure 9 ). Three regulated galaxy masses that were previously underestimated are now captured within the uncertainties. The mass estimate for g 15807, previously a large outlier, is also notably improved. Figure 12. Results from the sensitivity test: mass estimates after selecting tracers outside of r = 7.5 r s ). True values are shown as blue diamonds, estimates are dark purple circles, and the 95% c.r. are shown as errorbars. In light of this result, and evidence presented in Section 5.1.3 , we suggest that the combination of the GC analog number density profile, the percentage of complete data at small r , and the incomplete data at large r are the culprits of the mismatch between the predicted and true mass profiles. To test this hypothesis, one could rerun the analysis in a future sensitivity test, gradually increasing the number of proper motion measurements at large distances. We leave this to a future work. 5.4. Discussion The underestimation of the total mass appears to be a systematic bias in our method, as it applies to these MUGS2 galaxies—especially the regulated variety. Although it may be tempting to extrapolate results from these blind tests to our previous MW results using GCs in Paper 3 , it is important to make this kind of inference cautiously, for a few reasons: (1) The GC analog populations are dissimilar to the MW, and the MUGS2 galaxies, in the end,
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