Constraints on the frequency and mass content of r-process events derived from turbulent mixing in galactic disks
Abstract Metal-poor stars in the Milky Way (MW) halo display large star-to-star dispersion in their r-process abundance relative to lighter elements. This suggests a chemically diverse and unmixed interstellar medium (ISM) in the early Universe. This study aims to help shed light on the impact of turbulent mixing, driven by core collapse supernovae (cc-SNe), on the r-process abundance dispersal in galactic disks. To this end, we conduct a series of simulations of small-scale galaxy patches which resolve metal mixing mechanisms at parsec scales. Our set-up includes cc-SNe feedback and enrichment from r-process sources. We find that the relative rate of the r-process events to cc-SNe is directly imprinted on the shape of the r-process distribution in the ISM with more frequent events causing more centrally peaked distributions. We consider also the fraction of metals that is lost on galactic winds and find that cc-SNe are able to efficiently launch highly enriched winds, especially in smaller galaxy models. This result suggests that smaller systems, e.g. dwarf galaxies, may require higher levels of enrichment in order to achieve similar mean r-process abundances as MW-like progenitors systems. Finally, we are able to place novel constraints on the production rate of r-process elements in the MW,6×10−7M⊙/yr≲m˙rp≪4.7×10−4M⊙/yr, imposed by accurately reproducing the mean and dispersion of [Eu/Fe] in metal-poor stars. Our results are consistent with independent estimates from alternate methods and constitute a significant reduction in the permitted parameter space.
Supernova-driven turbulent metal mixing in high redshift galactic disks: metallicity fluctuations in the interstellar medium and its imprints on metal poor stars in the Milky Way
Anne Noer Kolborg, Davide Martizzi, Enrico Ramirez-Ruiz, Hugo Pfister, Charli Sakari, Risa H. Wechsler, Melinda Soares-Furtado
Abstract The extent to which turbulence mixes gas in the face of recurrent infusions of fresh metals by supernovae (SN) could help provide important constraints on the local star formation conditions. This includes predictions of the metallicity dispersion amongst metal poor stars, which suggests that the interstellar medium was not very well mixed at these early times. The purpose of this {\it Letter} is to help isolate, via a series of numerical experiments, some of the key processes that regulate turbulent mixing of SN elements in galactic disks. We study the gas interactions in small simulated patches of a galaxy disk with the goal of resolving the small-scale mixing effects of metals at pc scales, which enables us to measure the turbulent diffusion coefficient in various galaxy environments. By investigating the statistics of variations ofαelements in these simulations, we are able to derive constraints not only on the allowed range of intrinsic yield variations in SN explosions but also on the star formation history of the Milky Way. We argue that the observed dispersion of [Mg/Fe] in metal poor halo stars is compatible with the star-forming conditions expected in dwarf satellites or in an early low star-forming Milky Way progenitor. In particular, metal variations in stars that have not been phase-mixed can be used to infer the star-forming conditions of disrupted dwarf satellites.
