Evolution of globular-cluster systems of ultra-diffuse galaxies due to dynamical friction in MOND gravity

Abstract

Context. Dynamical friction can be used to distinguish Newtonian gravity and modified Newtonian dynamics (MOND) because it works differently in these frameworks. This concept, however, has yet to be explored very much with MOND. Previous simulations showed weaker dynamical friction during major mergers for MOND than for Newtonian gravity with dark matter. Analytic arguments suggest the opposite for minor mergers. In this work, we verify the analytic predictions for MOND by high-resolution N-body simulations of globular clusters (GCs) moving in isolated ultra-diffuse galaxies (UDGs). Aims. We test the MOND analog of the Chandrasekhar formula for the dynamical friction proposed by Sánchez-Salcedo on a single GC. We also explore whether MOND allows GC systems of isolated UDGs to survive without sinking into nuclear star clusters. Methods. The simulations are run using the adaptive-mesh-refinement code Phantom of Ramses. The mass resolution is 20 M⊙ and the spatial resolution 50 pc. The GCs are modeled as point masses. Results. Simulations including a single GC reveal that, as long as the apocenter of the GC is over about 0.5 effective radii, the Sánchez-Salcedo formula works excellently, with an effective Coulomb logarithm increasing with orbital circularity. Once the GC reaches the central kiloparsec, its sinking virtually stops, likely because of the core stalling mechanism. In simulations with multiple GCs, many of them sink toward the center, but the core stalling effect seems to prevent them from forming a nuclear star cluster. The GC system ends up with a lower velocity dispersion than the stars of the galaxy. By scaling the simulations, we extend these results to most UDG parameters, as long as these UDGs are not external-field dominated. We verify analytically that approximating the GCs by point masses has little effect if the GCs have the usual properties, but for massive GCs such as those observed in the NGC 1052-DF2 galaxy, further simulations with resolved GCs are desirable.

The formation of early-type galaxies through monolithic collapse of gas clouds in Milgromian gravity

“…As for now, POR has been successfully applied in the simulations of Antennae-like galaxies (Renaud et al 2016), simulations of the Sagittarius satellite galaxy (Thomas et al 2017), simulations of the Local Group producing the planes of satellites (Bílek et al 2018(Bílek et al , 2021bBanik et al 2022), simulations of streams from globular clusters (Thomas et al 2018), simulations of the formation of exponential disk galaxies (Wittenburg et al 2020), the global stability of M33 (Banik et al 2020), the evolution of globular-cluster systems of ultra-diffuse galaxies due to dynamical friction (Bílek et al 2021a) and polar-ring galaxies have also been successfully modelled with a pre-POR code (Lüghausen et al 2013). A detailed user-guide can be found in Nagesh et al (2021).…”

Dwarf Galaxies with Central Cores in Modified Newtonian Dynamics Gravity

“…This difficulty is confirmed by the few existing numerical simulations of galaxy formation and evolution using MOND acceleration. The central density drop is missing in all simulated galaxies, whether they are massive (Combes 2014;Bílek et al 2018), intermediate-mass (Roshan et al 2021), or even dwarfs (Bílek et al 2021, M å ; 2 × 10 8 M e ). Baryons are present in the centers of spheroids as well as in disks (Tiret & Combes 2007;Wittenburg et al 2020).…”

Distinguishing Dark Matter Cusps from Cores Using Globular Clusters

“…Dynamical studies of GC populations have been used to characterize dark matter halos observationally in the past (e.g., Tremaine et al 1975;Tremaine 1976), and recent works have included both entirely semianalytic (Gnedin et al 2014;Sánchez-Salcedo & Lora 2022) and more realistic N-body simulations of varying degrees of complexity (Cole et al 2012;Arca-Sedda & Capuzzo-Dolcetta 2017;Nusser 2018;Dutta Chowdhury et al 2019Bílek et al 2021;Bar et al 2022). The key principle behind all of these analyses is the same: dynamical friction (Chandrasekhar 1943) due to the halo acts on the GCs to cause their orbits to inspiral at a rate dependent on the local halo properties, as well as the GC mass (Hernandez & Gilmore 1998).…”