On the origin of mass-metallicity relations, blue tilts and scaling relations for metal-poor globular cluster systems

We investigate formation processes and physical properties of globular cluster systems (GCSs) in galaxies based on high-resolution cosmological simulations with globular clusters. We focus on metal-poor clusters (MPCs) and correlations with their host galaxies by assuming that MPC formation is truncated at a high redshift (ztrun≥ 6). We find that the correlation between mean metallicities (Zgc) of MPCs and their host galaxy luminosities (L) flattens from z=ztrun to 0. We also find that the observed relation (Zgc∝L0.15) in MPCs can be reproduced well in the models with Zgc∼L0.5 at z=ztrun when ztrun∼ 10, if mass-to-light ratios are assumed to be constant at z=ztrun. A flatter L–Zgc at z=ztrun is found to be required to explain the observed relation for constant mass-to-light ratio models with lower z=ztrun. However, better agreement with the observed relation is found for models with different mass-to-light ratios between z=ztrun and 0. It is also found that the observed colour–magnitude relation of luminous MPCs (i.e. ‘blue tilts’) may only have a small contribution from the stripped stellar nuclei of dwarf galaxies, which have nuclei masses that correlate with their total mass at z=ztrun. The simulated blue tilts are found to be seen more clearly in more massive galaxies, which reflects the fact that more massive galaxies at z= 0 are formed from a larger number of dwarfs with stellar nuclei formed at z > ztrun. The half-number radii (Re) of GCSs, velocity dispersions of GCSs (σ) and their host galaxy masses (Mh) are found to be correlated with one another such that Re∝Mh0.57 and σ∝Mh0.32. Based on these results, we discuss the link between hierarchical merging histories of galaxies and the physical properties of MPCs, the origin of the L–Zgc relation and non-homology of GCSs.