Reconciling dwarf galaxies with LCDM cosmology: Simulating a realistic population of satellites around a Milky Way-mass galaxy (1602.05957v2)

Abstract: Low-mass "dwarf" galaxies represent the most significant challenges to the cold dark matter (CDM) model of cosmological structure formation. Because these faint galaxies are (best) observed within the Local Group (LG) of the Milky Way (MW) and Andromeda (M31), understanding their formation in such an environment is critical. We present first results from the Latte Project: the Milky Way on FIRE (Feedback in Realistic Environments). This simulation models the formation of a MW-mass galaxy to z = 0 within LCDM cosmology, including dark matter, gas, and stars at unprecedented resolution: baryon particle mass of 7070 Msun with gas kernel/softening that adapts down to 1 pc (with a median of 25 - 60 pc at z = 0). Latte was simulated using the GIZMO code with a mesh-free method for accurate hydrodynamics and the FIRE-2 model for star formation and explicit feedback within a multi-phase interstellar medium. For the first time, Latte self-consistently resolves the spatial scales corresponding to half-light radii of dwarf galaxies that form around a MW-mass host down to Mstar > 10^5 Msun. Latte's population of dwarf galaxies agrees with the LG across a broad range of properties: (1) distributions of stellar masses and stellar velocity dispersions (dynamical masses), including their joint relation; (2) the mass-metallicity relation; and (3) a diverse range of star-formation histories, including their mass dependence. Thus, Latte produces a realistic population of dwarf galaxies at Mstar > 10^5 Msun that does not suffer from the "missing satellites" or "too big to fail" problems of small-scale structure formation. We conclude that baryonic physics can reconcile observed dwarf galaxies with standard LCDM cosmology.

• The paper reconciles observed dwarf galaxy properties with ΛCDM predictions by employing high-resolution simulations.
• The study uses the FIRE-2 model with adaptive hydrodynamics and detailed stellar feedback to resolve satellite structures as small as 10^5 solar masses.
• The paper demonstrates that incorporating baryonic processes mitigates the 'missing satellites' and 'too big to fail' problems by aligning dark matter distributions with observed core structures.

Simulating Dwarf Galaxies within the ΛCDM Framework: An Analysis of the Latte Project

The paper "Reconciling dwarf galaxies with ΛCDM cosmology" by Wetzel et al. presents significant advancements in the simulation of dwarf galaxies within the framework of cold dark matter (CDM) cos-mology. The focus of this paper is the "Latte Project," which aims to simulate a Milky Way-mass galaxy with unprecedented resolution using the Feedback in Realistic Environments (FIRE-2) model. The research addresses fundamental issues in cosmology, particularly the challenges posed by observations of dwarf galaxies in the Local Group.

Objectives and Methodology

The core objective of the paper is to reconcile the observational data of dwarf galaxies with predictions made by the standard ΛCDM cosmology. This is achieved by conducting high-resolution simulations of a Milky Way-like galaxy, incorporating both stellar and baryonic physics. The research employs the GIZMO code with a mesh-free method, providing adaptive hydrodynamics and incorporating dark matter, gas, and stars. This approach offers resolutions capable of resolving the half-light radii of dwarf galaxies, something that has been previously unattainable in such simulations.

Key Findings

1. Resolution of Long-standing Problems: The paper effectively addresses the "missing satellites" and "too big to fail" problems. It demonstrates that baryonic processes allow for a population of dwarf galaxies consistent with the Local Group, thereby resolving discrepancies between predicted and observed satellite galaxies around the Milky Way.
2. A Realistic Population of Dwarf Galaxies: The simulations indicate a population of dwarf galaxies exhibiting properties in line with observations, including stellar mass distributions, velocity dispersions, and metallicity relations. Importantly, the simulations extend down to galaxies with stellar masses ≥ $10^5 M_{\odot}$, a significant improvement over previous models.
3. Role of Stellar Feedback: By resolving spatial scales and incorporating state-of-the-art stellar feedback processes, the simulations showcase how baryonic feedback processes can significantly alter dark matter distributions, contributing to observed core structures in dwarf galaxies, deviating from previously predicted cuspy profiles by pure dark matter models.

Implications

The research presented in this paper has profound implications in both theoretical and observational cosmology. The successful resolution of dwarf galaxy properties within the CDM framework strengthens the validity of the ΛCDM model, which is foundational to our understanding of large-scale structure formation. The paper also underscores the necessity of incorporating baryonic physics into simulations to account for the complexity observed in real galaxies, paving the way for more accurate modeling of galaxy formation and evolution.

Future Directions

With the successful application of the FIRE-2 model in high-resolution simulations, future research may explore the dynamic and chemical evolution of these systems, examining aspects such as star formation histories and their cessation (quenching) in satellite galaxies. Further work could also explore the impact of varying initial conditions and feedback mechanisms to comprehensively understand their role in shaping the galaxy population.

In summary, Wetzel et al.'s research represents a significant step forward in cosmological simulations, offering a robust methodology for aligning theoretical predictions with astronomical observations of dwarf galaxies, thus reinforcing the standard model of cosmology. The implications for understanding the formation and evolution of galaxies in a ΛCDM universe are wide-ranging, offering new avenues for exploration in both simulations and observations.