[Paper Review] SN-driven mechanism of cusp-core transformation: an appraisal

Jan D. Burger, Jesús Zavala|arXiv (Cornell University)|Mar 1, 2021

Galaxies: Formation, Evolution, Phenomena4 references4 citations

TL;DR

This paper introduces an effective N-body model to simulate supernova (SN) feedback effects on dark matter (DM) cores in isolated dwarf galaxy halos, showing that core formation depends primarily on total injected energy, with faster injection and higher baryonic concentration enhancing core size. Crucially, impulsive potential changes in phase space do not guarantee core formation, revealing a decoupling between kinematic signatures and actual cored profiles.

ABSTRACT

We present and test an effective model for N -body simulations that aims at mimicking the impact of supernova (SN) feedback on the dark matter (DM) distribution of isolated halos hosting dwarf galaxies. Although the model is physically decoupled from the cosmological history of both the DM halo and the dwarf galaxy, it allows us to study the impact of different macroscopic parameters such as galaxy concentration, feedback energy and energy injection time in the process of SN-driven core formation in a physically clear way. Using our effective model in a suite of N-body simulations of an isolated halo with different SN feedback parameters, we find that whether or not a DM core forms is determined by the total amount of SN feedback energy that is transferred to the DM particles. At a fixed injected energy, the amount of transferred energy is bigger - and the size of the DM core is larger - the faster the energy injection occurs and the more compact the dwarf galaxy is. Analyzing the orbital evolution of kinematic tracers, we demonstrate that a core forms through SN feedback only if the energy injection is impulsive relative to the dynamical timescale of particles in the inner halo. However, there is no fundamental link between the total amount of injected energy and the injection rate. Consequently, the presence of signatures of impulsive changes of the gravitational potential is not a sufficient condition for dwarf-size halos to have cored density profiles.

Motivation & Objective

• To investigate how supernova feedback alters dark matter profiles in isolated dwarf galaxy halos.
• To determine the conditions under which SN feedback forms stable DM cores rather than cusps.
• To assess whether kinematic signatures of impulsive feedback reliably indicate core formation.
• To disentangle the roles of energy injection timescale, total energy, and baryonic concentration in core development.
• To test whether phase-space signatures of impulsive feedback can distinguish adiabatic from impulsive core formation.

Proposed method

• An effective N-body model is developed that decouples baryonic feedback from cosmological history, enabling controlled study of SN feedback effects.
• The model uses an external potential (Plummer or disk-like) to represent stellar distribution and injects energy into DM particles in a physically consistent manner.
• Energy injection is parameterized by a coupling strength ε and injection timescale τ, allowing systematic variation of feedback duration and amplitude.
• Simulations are run on a single isolated halo with varying baryonic concentration, feedback energy (ε), and injection timescale (τ).
• Tracer particles are used to analyze orbital evolution and phase-space structure to detect signatures of impulsive potential changes.
• The model isolates the impact of macroscopic parameters—energy, injection timescale, and concentration—on core formation, independent of full hydrodynamics.

Experimental results

Research questions

• RQ1 Does the total amount of SN feedback energy determine whether a dark matter core forms in a dwarf galaxy halo?
• RQ2 How does the timescale of energy injection affect core formation, especially relative to the halo's dynamical timescale?
• RQ3 Can kinematic signatures in phase space reliably indicate the presence of a cored DM profile?
• RQ4 Is there a fundamental link between impulsive potential changes and actual core formation, or can such signatures appear without cores?
• RQ5 How do baryonic concentration and feedback energy coupling jointly influence core size and stability?

Key findings

• Core formation in dwarf galaxy halos is primarily determined by the total amount of SN feedback energy injected into the dark matter distribution.
• For a fixed energy input, faster injection timescales and higher baryonic concentration lead to larger, more stable DM cores.
• Even with impulsive energy injection, cores do not form if the total energy is too low (e.g., ε = 0.01), despite detectable phase-space signatures.
• Kinematic signatures of impulsive feedback—such as radial expansion and orbital diffusion—can appear in phase space even when no core forms, indicating that such signatures are not sufficient indicators of core formation.
• When energy injection is slow (τ ≳ 10% of dynamical time), cores fail to form for low to moderate energy couplings, even if the potential change is abrupt.
• For high energy coupling (ε = 0.4), cores form and phase-space signatures persist even with slow injection, due to the magnitude of the potential change exceeding the dynamical timescale threshold.