We use a semi-analytic model for globular cluster (GC) formation built on dark matter merger trees to explore the relative role of formation physics and hierarchical assembly in determining the properties of GC populations. Many previous works have argued that the observed linear relation between total GC mass and halo mass points to a fundamental GC -dark matter connection or indicates that GCs formed at very high redshift before feedback processes introduced nonlinearity in the baryon-to-dark matter mass relation. We demonstrate that at M vir (z = 0) 10 11.5 M , a constant ratio between halo mass and total GC mass is in fact an almost inevitable consequence of hierarchical assembly: by the central limit theorem, it is expected at z = 0 independent of the GC-to-halo mass relation at the time of GC formation. The GC-to-halo mass relation at M vir (z = 0) < 10 11.5 M is more sensitive to the details of the GC formation process. In our fiducial model, GC formation occurs in galaxies when the gas surface density exceeds a critical value. This model naturally predicts bimodal GC color distributions similar to those observed in nearby galaxies and reproduces the observed relation between GC system metallicity and halo mass. It predicts that the cosmic GC formation rate peaked at z ∼ 4, too late for GCs to contribute significantly to the UV luminosity density during reionization.

Globular cluster (GC) systems around galaxies of a vast mass range show remarkably simple scaling relations. The combined mass of all GCs is a constant fraction of the total galaxy mass and the mean metallicity and metallicity dispersion of the GC system scale up weakly with galaxy mass. The metallicity of massive, metal-poor ("blue") clusters increases with cluster mass, while that of metal-rich ("red") clusters does not. A significant age-metallicity relation emerges from analysis of resolved stellar populations in Galactic GCs and unresolved populations in nearby galaxies. Remarkably, all these trends can be explained by a simple merger-based model developed in previous work and updated here using recent observations of galaxy scaling relations at high redshift.We show that the increasing dispersion of GC metallicity distributions with galaxy mass is a robust prediction of the model. It arises from more massive galaxies having more mergers that combine satellite GC systems. The average metallicity also increases by 0.6 dex over 3 dex in halo mass. The models show a non-linear trend between the GC system mass and host galaxy mass which is consistent with the data. The model does not consider GC self-enrichment, yet predicts a correlation between cluster mass and metallicity for massive blue clusters. The age-metallicity relation is another robust prediction of the model. Half of all clusters are predicted to form within the redshift range 5 < z < 2.3, corresponding to ages of 10.8 − 12.5 Gyr, in halos of masses 10 11 − 10 12.5 M .

We present BVRI and unfiltered light curves of 93 Type Ia supernovae (SNe Ia) from the Lick Observatory Supernova Search (LOSS) follow-up program conducted between 2005 and 2018. Our sample consists of 78 spectroscopically normal SNe Ia, with the remainder divided between distinct subclasses (3 SN 1991bg-like, 3 SN 1991T-like, 4 SNe Iax, 2 peculiar, and 3 super-Chandrasekhar events), and has a median redshift of 0.0192. The SNe in our sample have a median coverage of 16 photometric epochs at a cadence of 5.4 d, and the median first observed epoch is ∼4.6 d before maximum B-band light. We describe how the SNe in our sample are discovered, observed, and processed, and we compare the results from our newly developed automated photometry pipeline to those from the previous processing pipeline used by LOSS. After investigating potential biases, we derive a final systematic uncertainty of 0.03 mag in BVRI for our data set. We perform an analysis of our light curves with particular focus on using template fitting to measure the parameters that are useful in standardizing SNe Ia as distance indicators. All of the data are available to the community, and we encourage future studies to incorporate our light curves in their analyses.

Globular cluster (GC) systems demonstrate tight scaling relations with the properties of their host galaxies. In previous work, we developed an analytic model for GC formation in a cosmological context and showed that it matches nearly all of the observed scaling relations across 4 orders of magnitude in host galaxy mass. Motivated by the success of this model, we investigate in detail the physical origins and evolution of these scaling relations. The ratio of the combined mass in GCs M GC to the host dark matter halo mass M h is nearly constant at all redshifts, but its normalization evolves by a factor of ∼10 from birth to z = 0. The relation is steeper than linear at halo masses M h 10 11.5 M , primarily due to non-linearity in the stellar mass-halo mass relation. The near constancy of the ratio M GC /M h , combined with the shape of the stellar mass-halo mass relation, sets the characteristic U−shape of the GC specific frequency as a function of host galaxy mass. The contribution of accreted satellite galaxies to the buildup of GC systems is a strong function of the host galaxy mass, ranging from ≈0% at M h ≈ 10 11 M to 80% at M h ≈ 10 15 M . The metal-poor clusters are significantly more likely to form ex-situ relative to the metal-rich clusters, but a substantial fraction of metal-poor clusters still form in-situ in lower mass galaxies. Similarly, the fraction of red clusters increases from ≈ 10% at M h = 10 11 M to ≈ 60% at M h ≈ 10 13 M , and flattens at higher M h . Clusters formation occurs essentially continuously at high redshift, while at low redshift galactic mergers become increasingly important for cluster formation.