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Globular clusters (GCs) are sensitive tracers of galaxy assembly histories but interpreting the information they encode is challenging because mergers are thought to promote both the formation and disruption of GCs. We use simulations with controlled merger histories to examine the influence of merger mass ratio on the GC population of a present-day $L^\ast$ galaxy, using the genetic modification technique to adjust the initial conditions of a galaxy that experiences major mergers at $z = 1.7$ and $z = 0.77$ (ORGANIC case), so the later merger has twice its original mass ratio (ENHANCED case), or is prevented from occurring (SUPPRESSED case). We evolve the three realizations with E-MOSAICS, which couples sub-grid star cluster formation and evolution models to the EAGLE galaxy formation model. Relative to the ORGANIC case, the mass of surviving GCs is elevated (reduced) in the ENHANCED (SUPPRESSED) case, indicating that major mergers promote a net boost to the GC population. The boost is clearly quantified by the GC specific mass, $S_{\rm M}$, because it is sensitive to the number of the most massive GCs, whose long characteristic disruption timescales enable them to survive their hostile natal environments. In contrast, the specific frequency, $T_{\rm N}$, is insensitive to assembly history because it primarily traces low-mass GCs that tend to be disrupted soon after their formation. The promotion of GC formation and disruption by major mergers imprints a lasting and potentially observable signature: an elevated mass fraction of field stars in the galaxy's stellar halo that were born in star clusters., Comment: 17 pages, 8 figures. Submitted, comments welcome

We present an analysis of \textit{HST}/COS/G160M observations of CIV in the inner circumgalactic medium (CGM) of a novel sample of eight z$\sim$0, L$\approx$L$^{\star}$ galaxies, paired with UV-bright QSOs at impact parameters ($R_\mathrm{proj}$) between 25-130 kpc. The galaxies in this stellar-mass-controlled sample (log$_{10}$M$_{\star}$/M$_{\odot}$ $\sim$ 10.2-10.9 M$_{\odot}$) host super-massive black holes (SMBHs) with dynamically-measured masses spanning log$_{10}$M$_\mathrm{BH}$/M$_{\odot}$ $\sim$ 6.8-8.4; this allows us to compare our results with models of galaxy formation where the integrated feedback history from the SMBH alters the CGM over long timescales. We find that the \ion{C}{IV} column density measurements (N$_{\rm C IV}$) (average log$_{10}$N$_{\rm C IV, CH}$ = 13.94$\pm$0.09 cm$^{-2}$) are largely consistent with existing measurements from other surveys of N$_{\rm C IV}$ in the CGM (average log$_{10}$N$_{\rm C IV, Lit}$ = 13.90$\pm$0.08 cm$^{-2}$), but do not show obvious variation as a function of the SMBH mass. In contrast, specific star-formation rate (sSFR) is highly correlated with the ionized content of the CGM. We find a large spread in sSFR for galaxies with log$_{10}$M$_\mathrm{BH}$/M$_{\odot}$ $>$ 7.0, where the CGM \ion{C}{IV} content shows clear dependence on galaxy sSFR but not M$_\mathrm{BH}$. Our results do not indicate an obvious causal link between CGM CIV and the mass of the galaxy's SMBH; however through comparisons to the EAGLE, Romulus25, $\&$ IllustrisTNG simulations, we find that our sample is likely too small to constrain such causality., Comment: Accepted to ApJ, 28 pages, 7 figures