Simulating an Isolated Dwarf Galaxy with Multi-Channel Feedback and Chemical Yields from Individual Stars

Abstract: In order to better understand the relationship between feedback and galactic chemical evolution, we have developed a new model for stellar feedback at grid resolutions of only a few parsecs in global disk simulations, using the adaptive mesh refinement hydrodynamics code Enzo. For the first time in galaxy scale simulations, we simulate detailed stellar feedback from individual stars including asymptotic giant branch winds, photoelectric heating, Lyman-Werner radiation, ionizing radiation tracked through an adaptive ray-tracing radiative transfer method, and core collapse and Type Ia supernovae. We furthermore follow the star-by-star chemical yields using tracer fields for 15 metal species: C, N, O, Na, Mg, Si, S, Ca, Mn, Fe, Ni, As, Sr, Y, and Ba. We include the yields ejected in massive stellar winds, but greatly reduce the winds' velocities due to computational constraints. We describe these methods in detail in this work and present the first results from 500~Myr of evolution of an isolated dwarf galaxy with properties similar to a Local Group, low-mass dwarf galaxy. We demonstrate that our physics and feedback model is capable of producing a dwarf galaxy whose evolution is consistent with observations in both the Kennicutt-Schmidt relationship and extended Schmidt relationship. Effective feedback drives outflows with a greater metallicity than the ISM, leading to low metal retention fractions consistent with observations. Finally, we demonstrate that these simulations yield valuable information on the variation in mixing behavior of individual metal species within the multi-phase interstellar medium.

• The paper presents a novel simulation framework for isolated dwarf galaxies, tracking feedback and chemical yields from individual stars rather than averaged populations.
• The simulation incorporates multi-channel stellar feedback (winds, radiation, supernovae) and adaptive ray tracing to model interstellar medium structure and chemical enrichment.
• Key findings include the simulation reproducing star formation regulation, showing significant metal outflows from the galaxy, and revealing a multi-phase interstellar medium with varied chemical abundances.

Simulating an Isolated Dwarf Galaxy with Multi-Channel Feedback and Chemical Yields from Individual Stars

The study presented in "Simulating an Isolated Dwarf Galaxy with Multi-Channel Feedback and Chemical Yields from Individual Stars" explores the complexity of galactic evolution, particularly focusing on the feedback processes and chemical enrichment in an isolated low-mass dwarf galaxy. The research leverages a new simulation model that integrates multi-channel stellar feedback from individual stars, representing a significant advancement in capturing the detailed interplay between stellar evolution and the interstellar medium (ISM) across galaxy scales.

Key Simulation Advances

1. Star-by-Star Modeling: The simulations track feedback and chemical yields from stars as individual entities rather than averaging them into simple stellar populations. This approach enables a more detailed examination of the chemical enrichment process by tracing the yields from specific stars across their lifetimes.
2. Multi-Channel Feedback: The model incorporates a comprehensive set of feedback mechanisms, including stellar winds from both massive and asymptotic giant branch (AGB) stars, ionizing and non-ionizing radiation, and Supernova Types Ia and core-collapse events. Each of these channels has a distinct influence on the evolution of the ISM and enables a nuanced view of galaxy dynamics.
3. Adaptive Ray Tracing: A particularly novel aspect is the use of an adaptive ray tracing method to follow stellar ionizing radiation. This method provides insights into how different elements contribute to the structure and phases of the ISM, which are critical for studying star formation and feedback regulation.
4. Chemical Tagging: By tracking individual metal species (e.g., C, N, O, Fe), the simulations allow for unprecedented analysis of how metals mix, transport, and are ejected in galactic winds. This offers the potential to compare simulated results with stellar observations from large surveys like APOGEE and Gaia-ESO.

Numerical and Observational Implications

• Star Formation Regulation: The model's feedback mechanisms enforce a self-regulating star formation regime, aligning well with observed Es galaxy scaling laws such as the Kennicutt-Schmidt relation. This provides additional confidence in the model's ability to replicate the complex processes influencing observable galaxy properties.
• Metallicity and Outflows: The simulation outcomes indicate a significant fraction of metals produced by stellar processes are ejected beyond the galaxy disk and even the virial radius, consistent with observed trends in dwarf galaxies where metal retention is low.
• ISM Phase Structure: Simulations reveal a multi-phase ISM with varying chemical abundances, offering insight into the dynamical processes that transport and mix metals. Notably, variations in the abundance of nitrogen relative to oxygen point to differences in the mixing efficiency of metals based on their origins.

Future Directions and Challenges

The present work identifies several avenues for future exploration, such as refining the inclusion of binary star interactions and cosmic ray physics, both of which can affect feedback efficacy and ISM dynamics. The complexity and resource demands of the simulations limit the treatment of wind feedback to kinetic energy, prompting further research into fully capturing these dynamics.

Conclusion: The paper presents a sophisticated simulation framework that enhances understanding of galactic evolution processes, particularly through detailed tracking of feedback from individual stars. This methodology offers promising avenues for aligning simulations with observational data and developing predictive models of galaxy evolution across cosmic time. Future work will likely refine these models to further unravel the intricate network of processes that regulate dwarf galaxy evolution.