Fuzzy dark matter dynamical friction: Defying galactic cannibalism of globular clusters

TL;DR

This work examines how fuzzy dark matter (FDM) modifies dynamical friction (DF) acting on globular clusters (GCs), potentially preventing galactic cannibalism in dwarf galaxies. It implements the Lancaster20 FDM-DF formalism in galpy, enabling full orbital integrations across a wide range of halo-to-GC mass ratios and FDM boson masses $m_{22}$, and models halos with a solitonic core plus outer envelope. The authors identify three DF regimes controlled by $m_{22}$ and halo properties, showing that quantum granule heating and central cores can stall GC inspiral, naturally producing in-situ GC survival and a bimodal radial distribution in dwarfs, with observable implications for Euclid DR1. Their results offer a practical, testable avenue to constrain $m_{22}$ and distinguish FDM from CDM and SIDM using GC demographics, while providing a resolution to the Fornax timing problem.

Abstract

We present a new implementation of fuzzy dark matter (FDM) dynamical friction within the galpy framework, enabling orbital integrations of globular clusters (GCs) across a broad range of halo-to-GC mass ratios and boson masses. In this alternative DM scenario, dynamical friction is reduced or even suppressed by heating induced by FDM density granules. We further quantify the role of baryons and solitonic cores, natural consequences of FDM in galaxies, on the efficiency of orbital decay and the long-term survival of GCs. The most significant deviations from the cold DM (CDM) paradigm arise in the dwarf-galaxy regime, where FDM dynamical friction can stall the inspiral of GCs over a Hubble time, thereby preventing their sinking into galactic centers and halting the canonical galactic cannibalism of clusters. Importantly, our FDM-only friction model should be regarded as a conservative lower bound, since the inclusion of realistic FDM cores can only strengthen the survival of GCs through core stalling. This stalling mechanism not only preserves in-situ populations that would otherwise be erased in CDM, but also strongly suppresses the mixing of in-situ and ex-situ clusters, yielding a bimodal radial distribution of GCs. Our results show that the demographics of GC systems encode a distinct dynamical signature of FDM in dwarfs. These predictions open a new pathway to constrain the boson mass parameter with upcoming Euclid DR1 observations of extragalactic GCs, while simultaneously offering a natural explanation for the long-standing Fornax timing problem.

Figures (10)

• Figure 1: Computed FDM coefficient $\mathcal{C}_{\rm FDM}$ as function of the dimensionless parameter $kr$ for different regimes, assuming a fixed $M_\sigma=2$. Orange dashed line represents the classical coefficient $\mathcal{C}_\text{CDM}$, calculated with fixed $\Lambda=10^3$. The black dashed vertical lines mark $M_\sigma/2$ and $2M_\sigma$.
• Figure 2: FDM dynamical friction: Orbital radius as a function of time for a $10^6$ M$_\odot$ GC on circular (left panel) and radial (right panel) orbits within a static NFW halo, shown for different values of the FDM particle mass $m_{22}$. The dashed blue curve shows the evolution in the absence of any DF, while the dashed orange curve corresponds to the classical Chandrasekhar friction.
• Figure 3: Stalling of Fornax GC3: Orbital radius of GC3 (third row of Table \ref{['Table1']}) as a function of time, starting from its currently observed projected radius, assuming a circular orbit as the initial condition. Orange curves show orbital integrations using the classical Chandrasekhar DF formula, while green and magenta curves use the FDM DF model developed in this work. Solid orange and green lines correspond to orbits integrated in a cuspy NFW halo, while dashed orange and solid magenta lines represent orbits in a large-core halo model from 2012MNRAS.426..601C.
• Figure 4: Normalized total initial energy as a function of the normalized initial $z$-component of the angular momentum at $z=0$, color-coded by the infall time, for $10^6$ M$_\odot$ GCs orbiting within $10^9$ M$_\odot$ DM halos. Results are shown for CDM (left panels), FDM with only DF (middle panels), and FDM (right panels) with $m_{22} = 0.2, \, 6, \,$ and $80$. The infall time is defined as the time at which the apocentre of the GC orbit drops below $r_{\rm lim} = 0.157 \, \mathrm{kpc}$ (10% of the scale radius of a $10^9$ M$_\odot$ NFW halo). A total of 4500 gravitationally bound GCs were randomly initialized in logarithmic radius between $0.1$ and $10 \, r_s$. The energy is normalized to the absolute value of the minimum of the gravitational potential, $|E_{\rm min}|$, and the angular momentum to the absolute value of the maximum angular momentum in our GC sample.
• Figure 5: Top panel: DF efficiency map for FDM only model with halo-to-GC mass ratios between $10^3$ and $10^5$, and FDM particle masses $m_{22}$ ranging from 0.1 to 100. The secondary axis shows the corresponding halo mass assuming $M_{\mathrm{GC}} = 10^{6}$ M$_\odot$. The map is computed on a $16 \times 16$ grid, where each point corresponds to a NFW halo of a given mass and a DF force derived for a specific FDM particle mass. For each combination of halo-to-GC mass ratio and FDM particle mass, the DF efficiency is evaluated using 1000 orbits in order to limit computational cost. There were uniformly distributed in logarithmic space between $0.1$ and $10\,r_s$. The orange dashed and green solid lines indicate the 5% efficiency frontier for CDM and FDM-only models, respectively. Bottom panels: Orbital radius normalized to its initial value as a function of time, for GCs integrated over 10 Gyr in a $10^9$ M$_\odot$ NFW halo with classical DF (orange curves) and FDM DF (green curves) for $m_{22} = 0.16,\, 4,$ and $63$. For each case, both radial and circular orbits are shown. Dashed white lines separate the three regimes of FDM DF: (1) absence of friction inducing orbital stalling, (2) reduced friction, and (3) the classical regime.