In-situ globular clusters in alternative dark matter Milky Way galaxies: a first approach to fuzzy and core-like dark matter theories

TL;DR

This paper investigates how fuzzy dark matter (FDM) alters the dynamics and survival of in-situ globular clusters (GCs) in Milky Way–like galaxies by embedding mass-growth histories from the TNG50 simulation into time-evolving FDM potentials and evolving ~7,700 GCs. The authors identify three dynamical regimes controlled by the FDM particle mass parameter $m_{22}$: strong central baryon-dominated confinement for $m_{22} \lesssim 1$, CDM-like behavior around $m_{22} \approx 7$, and extended, more massive GC systems for $m_{22} \gtrsim 7$, with corresponding shifts in GC mass distributions and half-mass radii. They also extend the framework to warm and self-interacting DM, introducing a relative orbital index $I_{\rm orb}$ to compare phase-space availability across models, and discuss how current multi-scale constraints interact with these GC-based predictions. The work demonstrates that in-situ GC systems offer a sensitive, complementary probe of DM physics and could be constrained with Euclid and future surveys, though a full treatment requires inclusion of ex-situ clusters and more realistic baryonic physics.

Abstract

We present a first analysis of the dynamics of in-situ globular clusters (GCs) in Milky Way (MW)-like galaxies embedded in fuzzy dark matter (FDM) halos, combining cosmological assembly histories from the TNG50 simulation with dedicated orbital integrations and analytical models. GC populations are initialized with identical distributions in normalized $E$-$L_{z}$ in matched CDM and FDM halos. In a universe dominated by FDM, we identify three distinct regimes for the in-situ GC population depending on the particle mass $m_{22} \equiv m_χ/ 10^{-22}~\mathrm{eV}$. For $m_{22} < 7$, baryons dominate the inner potential, which remains steep and centrally concentrated, confining GC orbits to a narrow region and producing less massive, more compact systems than in CDM. For $m_{22} \sim 7$, GC properties resemble those in CDM, with similar mass and spatial distributions. For $m_{22} > 7$, the dark matter becomes both compact and globally dominant, generating a deeper and more extended gravitational potential that supports a wider range of stable GC orbits, resulting in more massive and spatially extended GC systems. Finally, we extend our framework to make predictions for GC populations in alternative DM models, including warm dark matter and self-interacting dark matter, in both MW-like and dwarf galaxies. Our findings demonstrate that in-situ GC systems offer a sensitive and independent probe of the underlying DM physics, opening new avenues for observational constraints with upcoming Euclid.

Figures (10)

• Figure 1: DM profiles of a $10^{10}~M_{\odot}$ halo at $z=0$ for different values of $m_{22}$ as in Spergel20. The dashed lines show the central solitonic profiles. The blue line shows the NFW profile of a $10^{10}~M_{\odot}$ halo at $z=0$. The solid lines show our model for the full halo profile, which is a combination of the FDM profile transitioning to an NFW profile, described by Equations \ref{['galpy1']} and \ref{['galpy2']}. The vertical lines indicate the size of the FDM core radius. The green solid line corresponds to the typical stellar density profile for this halo mass, extracted from the TNG50.
• Figure 2: FDM halo mass cut for TNG50 merged satellites: DM mass as a function of time for all merged satellites in the entire TNG50 sample. The hexagonal bins represent at least one satellite. The solid lines represent the low halo mass cutoff for different values of $m_{22}$. The cutoff for $m_{22} = 0.3$ (1.0) removes 6.4% (1.12%) of all satellites between $z=2$ and $z=0$. For $m_{22} \geq 7$, no halos are removed.
• Figure 3: Dynamical friction of merged satellites: Quantum Mach number as a function of the relative orbital distance for all merged satellites in the entire TNG50 sample between $z=2$ and $z=0$ for $m_{22} = 0.3$. The hexagonal bins represent regions containing at least one satellite. The red dashed line shows the adopted boundary between the FDM and CDM regimes, based on the quantum Mach number defined in Equation \ref{['MQN']}. The orange dashed line indicates the threshold where DM dynamical friction becomes efficient, as defined in Equation \ref{['ODF']}. The magenta box highlights the region of interest where FDM dynamical friction must be taken into account, but this only concerns 1.8$\%$ of the satellites.
• Figure 4: Confined-orbit versus expanded-orbit GCs: Initial conditions in left panels: Normalized total energy as a function of the normalized $z$-component of angular momentum at $z=2$ for in-situ GCs (points), used as initial conditions in two different MW host galaxies (IDs 529365 and 572328), under various DM models. The energy is normalized to the absolute value of the minimum of the gravitational potential, and the angular momentum is normalized to the absolute value of that of a circular orbit at the NFW scale radius $r_s$. The colored curves represent the orbital limits allowed by the gravitational potentials in the CDM (blue), FDM with $m_{22}=0.3$ (orange), and FDM with $m_{22}=7.0$ (purple) models. Time evolution in right panels: Galactocentric distances of GCs as function of time from $z=2$ to $z=0$, shown for the three DM models for two MW-like galaxies.
• Figure 5: Last apocenter in FDM as a function of the last apocenter in CDM for in-situ GCs across our entire MW sample for different DM models. The three colors represent different FDM models, with $m_{22} = 0.3$ (orange), $1.0$ (red), and $7.0$ (violet). The lines indicate the median values.