Kinematic Signatures of Impulsive Supernova Feedback in Dwarf Galaxies

Impulsive supernova feedback and nonstandard dark matter models, such as self-interacting dark matter (SIDM), are the two main contenders for the role of the dominant core formation mechanism at the dwarf galaxy scale. Here we show that the impulsive supernova cycles that follow episodes of bursty star formation leave distinct features in the distribution function of stars: groups of stars with similar ages and metallicities develop overdense shells in phase space. If cores are formed through supernova feedback, we predict the presence of such features in star-forming dwarf galaxies with cored host halos. Their systematic absence would favor alternative dark matter models, such as SIDM, as the dominant core formation mechanism.

Figure 1

Adiabatic and impulsive cusp-core transformation: Spherically averaged radial DM density of three different simulated dwarf-size halos after 3 Gyr of simulation time. The solid blue line corresponds to the CDM simulation with smooth star formation ($n_{\mathrm{th}}=0.1{\mathrm{cm}}^{-3}$), whereas the dashed green line denotes the result of the CDM simulation with bursty star formation ($n_{\mathrm{th}}=100{\mathrm{cm}}^{-3}$). The red dotted line corresponds to the SIDM simulation with smooth star formation ($n_{\mathrm{th}}=0.1{\mathrm{cm}}^{-3}$) and a self-interaction cross section ${\sigma }_T/m_{\chi }=1{\mathrm{cm}}^2{\mathrm{g}}^{-1}$.

Figure 2

Gas distributions of resulting galaxies after 3 Gyr of simulation time for two simulations with different star formation thresholds. We show face-on (left column) and edge-on (right column) projections of the gas density for the CDM simulation with smooth (top row) and bursty (bottom row) star formation. The side length of the field of view is 20 kpc in each panel, and we defined a coordinate system such that the $z$ axis is perpendicular to the gas disc. Notice how central gas is vertically expelled out of the disc plane in the simulation with bursty star formation. Such galactic outflows are characteristic of violent and impulsive events of supernova-driven energy release.

Figure 3

Average metallicity distribution (top panels) and mass-weighted distribution function (bottom panels) of star particles calculated after 3 Gyr of simulation time for two different simulations, projected into the radial phase space ($R$-$v_R$). Star particles are subject to a cut in stellar age; only stars which are 0.8–0.9 Gyr old are shown in these plots. Averaged stellar metallicity (mass-weighted distribution function) is color coded according to the scale on the right of each panel. For scale, we show a third of the escape velocity as a function of radius as black dashed lines. The left (right) column corresponds to the CDM simulation with smooth (bursty) star formation. Smooth star formation results in a smooth metallicity gradient with the more enriched starts in the center. Bursty star formation results in an overall weaker gradient, along with the presence of a shell of stars with high metallicity that intersects a low metallicity population at $R\sim 2\mathrm{kpc}$. This shell appears as a distinct overdense region in the mass-weighted distribution function.