Symphony: Cosmological Zoom-in Simulation Suites over Four Decades of Host Halo Mass

Abstract

We present Symphony, a compilation of 262 cosmological, cold-dark-matter-only zoom-in simulations spanning four decades of host halo mass, from 1011–1015 M ⊙. This compilation includes three existing simulation suites at the cluster and Milky Way–mass scales, and two new suites: 39 Large Magellanic Cloud-mass (1011 M ⊙) and 49 strong-lens-analog (1013 M ⊙) group-mass hosts. Across the entire host halo mass range, the highest-resolution regions in these simulations are resolved with a dark matter particle mass of ≈3 × 10−7 times the host virial mass and a Plummer-equivalent gravitational softening length of ≈9 × 10−4 times the host virial radius, on average. We measure correlations between subhalo abundance and host concentration, formation time, and maximum subhalo mass, all of which peak at the Milky Way host halo mass scale. Subhalo abundances are ≈50% higher in clusters than in lower-mass hosts at fixed sub-to-host halo mass ratios. Subhalo radial distributions are approximately self-similar as a function of host mass and are less concentrated than hosts’ underlying dark matter distributions. We compare our results to the semianalytic model Galacticus, which predicts subhalo mass functions with a higher normalization at the low-mass end and radial distributions that are slightly more concentrated than Symphony. We use UniverseMachine to model halo and subhalo star formation histories in Symphony, and we demonstrate that these predictions resolve the formation histories of the halos that host nearly all currently observable satellite galaxies in the universe. To promote open use of Symphony, data products are publicly available at http://web.stanford.edu/group/gfc/symphony.

Strong Dark Matter Self-interactions Diversify Halo Populations within and surrounding the Milky Way

“…Because of the volume of our high-resolution region, which extends to ≈10R vir of the MW host halo, there are significantly more isolated halos than subhalos. All mass functions rise toward low halo masses, with slopes consistent with previous measurements in zoom-in simulations (e.g., Nadler et al 2023). Interestingly, for halos down to our fiducial mass resolution limit of 10 8 M e h −1 , the SIDM mass function is nearly unchanged compared to the CDM case.…”

“…Our simulations' resolution allows us to robustly resolve both isolated halos and tidally evolved subhalos with present masses greater than 10 8 M e h −1 , corresponding to systems with >2500 particles at z = 0. In particular, this cut is well above the convergence limit for subhalo abundance measurements in zoom-in simulations (Nadler et al 2023), and is comparable to the particle count threshold necessary to robustly resolve the tidally stripped density profiles of CDM subhalos (Errani & Navarro 2021).…”

A Search for Faint Resolved Galaxies Beyond the Milky Way in DES Year 6: A New Faint, Diffuse Dwarf Satellite of NGC 55

“…If NGC 55-dw1 is interpreted as a satellite of NGC 55 its discovery is not entirely surprising. By applying the best-fit galaxy-halo connection model from Nadler et al (2020; described in Section 4.2) to the LMC-mass zoom-in simulations from the Symphony compilation (Nadler et al 2023), we predict that isolated LMC-mass halos host ≈one satellite of NGC 55-dw1's absolute magnitude, on average, among a total satellite population of ≈10 with M V  −3, consistent with predictions from other studies (e.g., Dooley et al 2017a). Thus, NGC 55-dw1 may naturally be interpreted as one of the brightest satellites of NGC 55, perhaps along with the M V ≈ −11 mag ESO 294-010, separated from NGC 55 by 120 kpc (Karachentsev et al 2002).…”

A Self-interacting Dark Matter Solution to the Extreme Diversity of Low-mass Halo Properties

“…We present a pair of CDM and SIDM cosmological DMonly zoom-in simulations centered on a host halo with M 200 = 1.1 × 10 13 M e using high-resolution initial conditions from the "Group" suite of Symphony simulations (Nadler et al 2023); throughout, we measure masses that enclose 200 times the critical density of the universe at z = 0. These simulations are run with a high-resolution particle mass of 3 × 10 5 h −1 M e and a Plummer-equivalent gravitational softening length of 170 h −1 pc using GADGET-2 (Springel 2005).…”