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1. Globular clusters as tracers of the dark matter content of dwarfs in galaxy clusters

   https://doi.org/10.1093/mnras/staa3915  

   Doppel, Jessica E; Sales, Laura V; Navarro, Julio F; Abadi, Mario G; Peng, Eric W; Toloba, Elisa; Ramos-Almendares, Felipe (February 2021, Monthly Notices of the Royal Astronomical Society)

   null (Ed.)

   ABSTRACT Globular clusters (GCs) are often used to estimate the dark matter content of galaxies, especially dwarf galaxies, where other kinematic tracers are lacking. These estimates typically assume spherical symmetry and dynamical equilibrium, assumptions that may not hold for the sparse GC population of dwarfs in galaxy clusters. We use a catalogue of GCs tagged on to the Illustris simulation to study the accuracy of GC-based mass estimates. We focus on galaxies in the stellar mass range 108–1011.8 M⊙ identified in nine simulated Virgo-like clusters. Our results indicate that mass estimates are, on average, accurate in systems with GC numbers NGC ≥ 10 and where the uncertainty of individual GC line-of-sight velocities is smaller than the inferred velocity dispersion, σGC. In cases where NGC ≤ 10, however, biases may result, depending on how σGC is computed. We provide calibrations that may help alleviate these biases in methods widely used in the literature. As an application, we find a number of dwarfs with $$M_{*} \sim 10^{8.5}\, \mathrm{M}_{\odot }$$ – comparable with the ultra-diffuse galaxy NGC 1052-DF2 (DF2), notable for the low σGC of its 10 GCs – that have $$\sigma _{\rm GC} \sim 7\!-\!15\, {\rm km \,s}^{-1}$$. These DF2 analogues correspond to relatively massive systems at their infall time (M200 ∼ 1–3 × 1011 M⊙), which have retained only 3–17 GCs and have been stripped of more than 95 per cent of their dark matter. Our results suggest that extreme tidal mass loss in otherwise normal dwarf galaxies may be a possible formation channel for ultra-diffuse objects such as DF2. 

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2. Modeling the kinematics of globular cluster systems

   https://doi.org/10.1093/mnras/stac1651  

   Chen, Yingtian; Gnedin, Oleg Y (July 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Globular clusters (GCs) are old massive star clusters that serve as ‘fossils’ of galaxy formation. The advent of Gaia observatory has enabled detailed kinematics studies of the Galactic GCs and revolutionized our understanding of the connections between GC properties and galaxy assembly. However, lack of kinematic measurements of extragalactic GCs limits the sample size of GC systems that we can fully study. In this work, we present a model for GC formation and evolution, which includes positional and kinematic information of individual GCs by assigning them to particles in the Illustris TNG50-1 simulation based on age and location. We calibrate the three adjustable model parameters using observed properties of the Galactic and extragalactic GC systems, including the distributions of position, systemic velocity, velocity dispersion, anisotropy parameter, orbital actions, and metallicities. We also analyse the properties of GCs from different origins. In outer galaxy, ex situ clusters are more dominant than the clusters formed in situ. This leads to the GC metallicities decreasing outwards due to the increasing abundance of accreted, metal-poor clusters. We also find the ex-situ GCs to have greater velocity dispersions and orbital actions, in agreement with their accretion origin. 

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3. Investigating the Ultra-diffuse Galaxy NGC5846_UDG1 through the Kinematics of its Rich Globular Cluster System

   https://doi.org/10.1093/mnras/staf559  

   Haacke, Lydia; Forbes, Duncan_A; Gannon, Jonah_S; Danieli, Shany; Brodie, Jean_P; Pfeffer, Joel; Romanowsky, Aaron_J; van Dokkum, Pieter; Janssens, Steven_R; Buzzo, Maria_Luisa; et al (April 2025, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Recent studies of ultra-diffuse galaxies (UDGs) have shown their globular cluster (GC) systems to be central in unveiling their remarkable properties and halo masses. Deep Hubble Space Telescope imaging revealed 54 GC candidates around the UDG NGC5846_UDG1 (UDG1), with a remarkable 13 per cent of the stellar light contained in the GC system. We present a kinematic analysis of UDG1’s GC system from observations with the integral field spectrograph Keck Cosmic Web Imager on the Keck II telescope. We measure recessional velocities for 19 GCs, confirming them as members of UDG1, giving a total of 20 confirmed GCs when combined with literature. Approximately, 9 per cent of the stellar light are contained just in the confirmed GCs. We determine the GC system’s velocity dispersion to be $$\sigma _{\rm GC}$$ = 29.8$$^{+6.4}_{-4.9}$$ km s$$^{-1}$$. We find that $$\sigma _{\rm GC}$$ increases with increasing magnitude, consistent with predictions for a GC system that evolved under the influence of dynamical friction. The GC system velocity dispersion is constant out to $${\sim} 1R_{\rm eff}$$. Using $$\sigma _{\rm GC}$$, we calculate $$M_{\rm dyn}$$ = $$2.09^{+1.00}_{-0.64}\times 10^{9}$$ M$$_{\odot }$$ as the dynamical mass enclosed within $$\sim$$2.5 kpc. The dark matter halo mass suggested by the GC number–halo mass relationship agrees with our dynamical mass estimate, implying a halo more massive than suggested by common stellar mass–halo mass relationships. UDG1, being GC-rich with a massive halo, fits the picture of a failed galaxy. 

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4. Origin of the correlation between stellar kinematics and globular cluster system richness in ultradiffuse galaxies

   https://doi.org/10.1093/mnras/stae850  

   Pfeffer, Joel; Janssens, Steven R.; Buzzo, Maria Luisa; Gannon, Jonah S.; Bastian, Nate; Bekki, Kenji; Brodie, Jean P.; Couch, Warrick J.; Crain, Robert A.; Forbes, Duncan A.; et al (March 2024, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Observational surveys have found that the dynamical masses of ultradiffuse galaxies (UDGs) correlate with the richness of their globular cluster (GC) system. This could be explained if GC-rich galaxies formed in more massive dark matter haloes. We use simulations of galaxies and their GC systems from the E-MOSAICS project to test whether the simulations reproduce such a trend. We find that GC-rich simulated galaxies in galaxy groups have enclosed masses that are consistent with the dynamical masses of observed GC-rich UDGs. However, simulated GC-poor galaxies in galaxy groups have higher enclosed masses than those observed. We argue that GC-poor UDGs with low stellar velocity dispersions are discs observed nearly face on, such that their true mass is underestimated by observations. Using the simulations, we show that galactic star formation conditions resulting in dispersion-supported stellar systems also leads to efficient GC formation. Conversely, conditions leading to rotationally supported discs lead to inefficient GC formation. This result may explain why early-type galaxies typically have richer GC systems than late-type galaxies. This is also supported by comparisons of stellar axis ratios and GC-specific frequencies in observed dwarf galaxy samples, which show GC-rich systems are consistent with being spheroidal, while GC-poor systems are consistent with being discs. Therefore, particularly for GC-poor galaxies, rotation should be included in dynamical mass measurements from stellar dynamics. 

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5. Why do some ultra diffuse Galaxies have rich globular cluster systems?

   https://doi.org/10.1093/mnras/stae2675  

   Forbes, Duncan_A; Buzzo, Maria_Luisa; Ferre-Mateu, Anna; Romanowsky, Aaron_J; Gannon, Jonah; Brodie, Jean_P; Collins, Michelle_L_M (December 2024, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Some ultra diffuse galaxies (UDGs) reveal many more globular clusters (GCs) than classical dwarf galaxies of the same stellar mass. These UDGs, with a mass in their GC system ($$M_{\rm GC}$$) approaching 10 per cent of their host galaxy stellar mass ($$M_{\ast }$$), are also inferred to have high halo mass to stellar mass ratios ($$M_{\rm halo}/M_{\ast }$$). They have been dubbed Failed Galaxies. It is unknown what role high GC formation efficiencies and/or low destruction rates play in determining the high $$M_{\rm GC}/M_{\ast }$$ ratios of some UDGs. Here we present a simple model, which is informed by recent JWST observations of lensed galaxies and by a simulation in the literature of GC mass loss and tidal disruption in dwarf galaxies. With this simple model, we aim to constrain the effects of GC efficiency/destruction on the observed GC richness of UDGs and their variation with the integrated stellar populations of UDGs. We assume no ongoing star formation (i.e. quenching at early times) and that the disrupted GCs contribute their stars to those of the host galaxy. We find that UDGs, with high $$M_{\rm GC}/M_{\ast }$$ ratios today, are most likely the result of very high GC formation efficiencies combined with modest rates of GC destruction. The current data loosely follow the model that ranges from the mean stellar population of classical dwarfs to that of metal-poor GCs as $$M_{\rm GC}/M_{\ast }$$ increases. As more data becomes available for UDGs, our simple model can be refined and tested further. 

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