Gannon, J. S., Di Cintio, A., Forbes, D. A., García-Bethencourt, G., Brodie, J. P., Libeskind, N., Couch, W. J., Hartke, J., 2025, Monthly Notices of the Royal Astronomical Society
, 544, 4 , 3094 Published: December 2025
In this work, we compare galaxies from the NIHAO and HESTIA simulation suites to ultra-diffuse galaxies (UDGs) with spectroscopically measured dynamical masses. For each observed UDG, we identify the simulated dark matter halo that best matches its dynamical mass. In general, observed UDGs are matched to simulated galaxies with lower stellar masses than they are observed to have. These simulated galaxies also have halo masses much less than would be expected given the observed UDG's stellar mass and the stellar mass─halo mass relationship. We use the recently established relation between globular cluster (GC) number and halo mass, which has been shown to be applicable to UDGs, to better constrain their observed halo masses. This method indicates that observed UDGs reside in relatively massive dark matter haloes. This creates a striking discrepancy: the simulated UDGs are matched to the dynamical masses of observed ones, but not their total halo masses. In other words, simulations can produce UDGs in haloes with the correct inner dynamics, but not with the massive haloes implied by GC counts. We explore several possible explanations for this tension, from both the observational and theoretical sides. We propose that the most likely resolution is that observed UDGs may have fundamentally different dark matter halo profiles than those produced in NIHAO and HESTIA. This highlights the need for a simulation that self-consistently produces galaxies of a stellar mass of $\sim 10^8 {\rm M}_\odot$ in dark matter haloes that exhibit the full range of large dark matter cores to cuspy NFW-like haloes.
Chisholm, R., D’Onghia, E., Libeskind, N., Lucchini, S., Fox, A. J., Steinmetz, M., 2025, The Astrophysical Journal
, 993, 1 , 67 Published: November 2025
We identify and investigate a preinfall analog of the Large and Small Magellanic Clouds (LMCs, SMCs) in the High-Resolution Environmental Simulations of the Immediate Area suite of constrained cosmological simulations. The system, dynamically isolated from the Local Group, evolves over ∼6 Gyr and forms a multiphase warm coronal halo and a neutral gas stream via repeated tidal interactions, ∼150 kpc in length. The LMC analog's corona forms self-consistently through virial accretion and inhibits the survival of clumpy neutral structures beyond ∼600 Myr. The SMC analog remains bound through to z = 0, and the pair also exhibits bridge-like and leading-arm features. These results suggest that while most of the ionized stream is formed by the LMC coronal gas, the neutral gas stream, bridge, and leading arm components of the Magellanic System can arise from dwarf─dwarf interactions prior to infall, while the survival and ionization of these features likely require additional environmental processing. Furthermore, we identify a stellar component out of phase to the neutral component of the stream, implying that if the Magellanic stellar stream exists, it may not be spatially coexistent to the dominant H I stream. This system offers a valuable preinfall reference point for interpreting the Magellanic System and identifying analogs beyond the Local Group.
Seidel, B. A., Dolag, K., Remus, R.-S., Sorce, J. G., Hernández-Martínez, E., Khabibullin, I., Aghanim, N., 2025, Astronomy and Astrophysics
, 702 , A243 Published: October 2025
Context. Large-scale agglomerations of galaxy clusters are the most massive structures in the Universe. To what degree they are actually bound against an accelerating expansion of the background cosmology is of significant cosmological as well as astrophysical interest. In this study, we introduce a crossmatched set of superclusters from the SLOW constrained simulations of the local (z < 0.05) Universe. These simulations combine a central region constrained by local velocity field data and realistic baryonic physics models within a 500 Mpc/h Box to reproduce the locally observed large-scale structure in detail. Aims. Identifying the local superclusters provides estimates on the efficacy of the constraints in reproducing the local large-scale structure accurately. The simulated counterparts can help to identify possible future observational targets containing interesting features, such as bridges between pre-merging and merging galaxy clusters and collapsing filaments, and provide comparisons for current observations. By numerically determining the collapse volumes for the simulated counterparts, we further elucidate the dynamics of cluster-cluster interactions in those regions. Methods. Starting from observational catalogs of local superclusters and the most massive clusters from the SLOW simulations already identified in previous works, we searched for simulated counterparts of supercluster members of six regions. We evaluated the significance of these detections by comparing the observed geometries to supercluster regions in random simulations. We then ran an N-body version of the SLOW initial conditions into the far future and determined which of the member clusters are gravitationally bound to the host superclusters. Furthermore we computed masses and density contrasts for the collapse regions. Results. We demonstrate that the SLOW constrained simulation of the local Universe accurately reproduces local supercluster regions not only in terms of the mass of their members but also in the individual clusters' 3D geometrical arrangement relative to each other. We furthermore find the bound regions of the local superclusters to be consistent in both size and density contrast with previous theoretical studies. This will allow us to connect future numerical zoom-in studies of the clusters to the large-scale environments and specifically the supercluster environments these local galaxy clusters evolve in. The zoom-ins will focus on ICM properties, turbulence, and nonthermal emission and build on the existing work concerned with the environments of local galaxy clusters.
The strongest experimental evidence for dark matter is the Galactic Center gamma-ray excess observed by the Fermi telescope and even predicted prior to discovery as a potential dark matter signature via weakly interacting massive particle dark matter self-annihilations. However, an equally compelling explanation of the excess gamma-ray flux refers to a population of old millisecond pulsars that also accounts for the observed boxy morphology inferred from the bulge old star population. We employ a set of Milky Way-like galaxies found in the HESTIA constrained simulations of the local universe to explore the rich morphology of the central dark matter distribution, motivated by the GAIA discovery of a vigorous early merging history of the Milky Way galaxy. We predict a significantly nonspherical gamma-ray morphology from the weakly interacting massive particle interpretation. Future experiments, such as the Cherenkov Telescope Array, that extend to higher energies, should distinguish between the competing interpretations.
Richter, P., Rünger, F., Lehner, N., Howk, J. C., Péroux, C., Libeskind, N., Steinmetz, M., de Jong, R., 2025, Astronomy and Astrophysics
, 701 , A76 Published: September 2025
Context. The Milky Way is surrounded by large amounts of hot gas at temperatures of T > 106 K, which represents a major baryon reservoir. Aims. We explore the prospects of studying the hot coronal gas in Milky Way halo by analyzing the highly forbidden optical coronal lines of [Fe X] and [Fe XIV] in absorption against bright (unrelated) extragalactic background sources. Methods. We used a semi-analytic model of the Milky Way's coronal gas distribution together wih HESTIA simulations of the Local Group and observational constraints to predict the expected Fe X and Fe XIV column densities, as well as the line shapes and strengths for the [Fe X] λ6374.5 and [Fe XIV] λ5302.9 transitions. We provide predictions for the signal-to-noise ratio (S/N) required to detect these lines. Using archival optical data from an original sample of 739 high-resolution AGN spectra from VLT/UVES and KECK/HIRES, we generated a stacked composite spectrum to measure an upper limit for the column densities of Fe X and Fe XIV in the Milky Way's coronal gas. Results. We predicted column densities of log N(Fe X) = 15.40 and log N(Fe XIV) = 15.23 in the Milky Way's hot halo, corresponding to equivalent widths of WFeX, 6347 = 190 μÅ and WFeXIV, 5302 = 220 μÅ. We estimated that a minimum S/N of ∼50 000(∼25 000) is required to detect [Fe X] λ6374.5 ([Fe XIV] λ5302.9) absorption at a 3σ level. There was no [Fe X] and [Fe XIV] detected in our composite spectrum, which achieves a maximum S/N = 1240 near 5300 Å. We derived 3σ upper column-density limits of log N(Fe X) ≤ 16.27 and log N(Fe XIV) ≤ 15.85, in line with the above-mentioned predictions. Conclusions. While [Fe X] and [Fe XIV] absorption is too weak to be detected with current optical data, we outline how upcoming extragalactic spectral surveys with millions of medium- to high-resolution optical spectra will provide the necessary sensitivity and spectral resolution to measure velocity-resolved [Fe X] and [Fe XIV] absorption in the Milky Way's coronal gas (and beyond). This opens up a new prospective window on studies of the dominant baryonic mass component of the Milky Way taking the form of hot coronal gas via optical spectroscopy.
