Is the stellar mass-stellar metallicity relation universal in the Milky Way satellites and beyond?

Abstract

Observations reveal a universal stellar mass-stellar metallicity relation (MZR) existing in Local Group dwarfs of different types, $Z_*\propto M_*^{\alpha}$ with $\alpha=0.30\pm0.02$. In this work, we investigate the "universality" of the MZRs for both satellites and central galaxies in a large number of different host dark matter halos covering a large mass range of $10^9$-$10^{15}h^{-1}M_\odot$, by using a semianalytical galaxy formation and evolution model. We obtain the following results. (1) The exponents ($\alpha$) for the MZRs of the satellites in halos with the same mass as the Milky Way halo but different individual assembly histories are mostly $\sim$0.2-0.4, i.e., having a scatter of $\sim 0.2$; and the scatter of $\alpha$ increases with decreasing halo masses. (2) The MZR relations are changed little by the variation of halo masses and the classification between central galaxies and satellites, if many halos with the same mass are stacked together. (3) A double power law exists in the MZR relations for both central galaxies and stacked satellites, with $\alpha\sim$0.2-0.4 at $10^3M_\odot< M_*<10^{8} M_\odot$ and a relatively higher $\alpha\sim0.5$ at $10^8M_\odot<M_*<10^{11}M_\odot$. (4) The high-mass satellites ($M_*>10^8M_\odot$) existing mostly in high-mass halos can lead to an apparent increase of $\alpha$ (from $\sim0.2$ to $\sim0.4$) with increasing host halo masses shown in the single power law fitting results of stacked satellites. The universality of the MZR suggests the common physical processes in stellar formation and chemical evolution of galaxies can be unified over a large range of galaxy masses and halo masses.