MARVELously Dark: the gravothermal evolution of dwarf halos in velocity-dependent SIDM

TL;DR

The study investigates gravothermal evolution in dwarf halos using a velocity-dependent SIDM model (Ms.Marvel DMO) and contrasts it with CDM baselines (Storm CDM DMO and Storm CDM+baryons). It demonstrates that SIDM induces core-formation at low masses and can drive core-collapse below $M_{\rm halo} \sim 2\times10^9\ M_$, with nine halos entering the core-collapse regime and achieving $\alpha < -2.0$ by $z=0$, while CDM with baryons forms cores only in higher-mass dwarfs. The authors validate a parametric gravothermal evolution model against measured core-formation and core-collapse timescales and show that core slope is a more robust diagnostic of collapse than central density, with its interpretation depending weakly on radius and merger history. These results imply that velocity-dependent SIDM can naturally reproduce the observed diversity of dwarf galaxy inner profiles and offer a practical pathway to constrain SIDM cross sections with current and future observations.

Abstract

Self-interacting dark matter (SIDM) with a sufficiently large cross section has been shown to naturally produce constant dark matter (DM) cores, as well as core-collapse, at the centers of dwarf halos on cosmic timescales, potentially reducing tensions with observation. Here, we present halos from a new dark matter only (DMO) cosmological (SIDM) simulation: Ms.Marvel DMO with a velocity-dependent self-interaction cross section with $σ/m_\text{max} = 50$ cm$^2$/g at $v_\text{max} = 35$ km/s. We compare these to the CDM suite of Storm simulations including both DMO and dark matter + hydrodynamics runs, in order to test core-formation (and core-collapse) across different dark matter models. We show that Ms.Marvel DMO can reproduce core slopes consistent with observations of isolated dwarf galaxies and more massive ($\text{M}_{vir} \gtrsim 10^{10} M_{\odot}$) CDM dwarf halos that include stellar feedback from the matched CDM run (Storm CDM+baryons). We identify nine Ms.Marvel SIDM DMO halos in the core-collapse phase of gravothermal evolution with halo masses below $2\times 10^9 M_{\odot}$. We find that using core slope to measure the core-collapse timescales of Ms.Marvel DMO halos agrees well with predicted collapse times estimated with the parametric model for SIDM halos introduced by \cite{Yang2023}. Additionally, compared to central density, core slope is less sensitive to both the radius of measurement and halo merger history. These results indicate that the slope of the inner DM density profile more cleanly differentiates core-collapsed versus core-forming halos than central density amplitude.

Figures (13)

• Figure 1: The effective cross section versus $V_\text{max}$ for Ms.Marvel (black), with comparisons from Fry2015 in pink and Correa_2022; SigmaConstant10 (dark red), SigmaVel20 (red), SigmaVel60 (orange red), and SigmaVel100 (orange). Velocity-dependent models are shown with solid lines and models with constant cross sections are shown with dashed lines. We include different models in this plot to contextualize our comparison between the inner slopes of the DM density profiles of dwarf halos from the Ms.Marvel simulation against halos from Correa_2022 and Fry2015 in a later section.
• Figure 2: Central core slope ($\alpha$) vs DM halo mass colored by central density. Colored circles, empty squares, and purple squares represent halos from the Ms.Marvel DMO, Storm CDM DMO, and Storm CDM+baryons simulations respectively. Grey points represent observed slopes in dwarf galaxies from Leung2021 (square), Oh2011slopes (up triangle), Oh2015 (down triangle), and Relatores2019 (diamond). Core slope of a smoothed DM density profile is measured between 0.26 and 0.39 kpc in each halo. Ms.Marvel halos are colored by corresponding central density, calculated as the averaged density within a radius of 0.33 kpc.
• Figure 3: Central core slope traced through time for Ms.Marvel DMO halos. Core slope of a smoothed DM density profile is measured between 0.26 and 0.39 kpc in each halo. Each solid line represents one halo, and lines are colored by halo central density at redshift zero. Halos are separated into different panels by halo mass measured at redshift zero, decreasing from left to right and from top to bottom. The black line represents the average core slope traced through time for the halos in each mass bin. Dark blue lines represent core slopes traced through time for Storm CDM+baryons halos. Core slopes are measured using the same methodology as in Figure \ref{['fig:Mvalpha']}.
• Figure 4: Central core slope traced through time for Storm CDM DMO halos. Core slope of a smoothed DM density profile is measured between 0.26 and 0.39 kpc in each halo. Each solid line represents one halo, and lines are colored by central density at redshift zero. Halos are separated into different panels by halo mass measured at redshift zero, decreasing from left to right and from top to bottom. The black line represents the average core slope traced through time for the halos in each mas bin. Dark blue lines represent core slopes traced through time for Storm CDM+baryons halos. Core slopes are measured using the same methodology as in Figure \ref{['fig:Mvalpha']}.
• Figure 5: Average central density measured within 0.35 kpc traced through time for Ms.Marvel DMO halos. Central density is normalized by dividing by the initial central density ($\rho_0$) of each halo. Each solid line represents one smoothed halo profile, and lines are colored by central density at redshift zero. Halos are separated into different panels by halo mass with mass decreasing from left to right and from the top to bottom rows. The black line represents the average densities traced through time for the halos in each panel. Dark blue lines represent central densities traced through time for Storm CDM+baryons halos. Central densities are calculated by taking the average central density contained within 0.35 kpc of the halo center normalized by initial central density.