The AIDA-TNG project: 3D halo shapes

Abstract

Context. The shapes of dark matter halos can be used to constrain the fundamental properties of dark matter. In standard Cold Dark Matter (CDM) cosmologies, halos are typically triaxial, with a preference for prolate configurations, particularly at low masses and high redshift. Aims. We focus on the characterization of total matter 3D shape in alternative dark matter models, such as Self-Interacting Dark Matter (SIDM) and Warm Dark Matter (WDM). These scenarios predict different structural properties due to collisional effects or the suppression of small-scale power. Methods. We measure the different halo component shapes - dark matter, stars and gas - at various radii from the center in the AIDA-TNG (Alternative Interacting Dark Matter and Astrophysics - TNG), which is a suite of high-resolution cosmological simulations built upon the IllustrisTNG framework. The intent is to systematically study how different dark matter models - specifically, SIDM and WDM - affect galaxy formation and the structure of dark matter halos, when realistic baryonic physics is also included. Results. SIDM models tend to produce rounder and more isotropic halos, especially in the inner regions, as a result of momentum exchange between dark matter particles. WDM halos are also slightly more spherical than their CDM counterparts, and are typically less concentrated. In all cases, the inclusion of self-consistent baryonic physics makes the central regions of all halos rounder, while still revealing clear distinctions among the various dark matter models. Conclusions. The general framework presented in this work, based on the 3D halo shape, can be useful to interpret multi-wavelength data analyses of galaxies and clusters.

Figures (8)

• Figure 1: Three-dimensional distribution of particles in stars (left), gas (center), and dark matter (right) of the most massive halo in the CDM simulation at $z=0$ having a mass $M_{200}=2.6 \times 10^{14}h^{-1}$M$_{\odot}$.
• Figure 2: Median profiles of minor-to-major (top) and intermediate-to-major (bottom) axis ratios for $z=0$ halos in the CDM simulation in bins of increasing mass (from left to right). Solid black curves show the total axis ratios in the FP run, while solid red, dotted gold, and solid orange curves show the corresponding results for the dark matter, gas, and stars, respectively. Dashed red curves show halos in the same mass bins but for the DMO run. Green data points (shown only in some of the boxes) consider the satellites and were weighted by stellar mass when computing the inertial mass tensor. The error bars bracket 25% and 75% of the distribution. The vertical bars display the resolution limit, which is equal to 10 times the softening length. The number of halos present in the four considered mass bins is: 305, 78, 34, and 14, respectively.
• Figure 3: Minor-to-major axis ratios for the DM models relative to the CDM value, for the same ($z=0$) mass bins as Fig. \ref{['fig_LCDM_Radius']}. Top and bottom panels display the results from FP and DMO runs, respectively.
• Figure 4: Median misalignment angles, as a function of the rescaled radius, of dark matter (red) and gas (orange) with respect to the star particles (yellow), in the AIDA-TNG simulations. Dashed, dot-dashed, and dotted lines refer to SIDM1, vSIDM, and WDM3 simulations, respectively, and the four panels are for the same mass bins as in Fig. \ref{['fig_LCDM_Radius']}. The colored shaded regions bracket the central 50% (i.e., between 25% and 75%) of the CDM measurements. The four panels refer to various mass bins as presented in Fig. \ref{['fig_LCDM_Radius']}
• Figure 5: Misalignment angle between the major axis of the BCG (estimated using the inner 50% of the star particles) and of its host dark matter halo (estimated from the total mass within $R_{200}$), shown as a function of half stellar mass of the BCG. Symbol size and color are proportional to the ratio between the central galaxy and host halo sizes for the CDM runs. A dashed gray band encloses 50% of the data points. Black, blue, green, and purple lines show the running median for the CDM, SIDM1, vSIDM, and WDM3 cases, respectively. Horizontal lines on the right indicate the median value, over all half stellar mass values, for the corresponding DM model.