Arakelyan, N. R., Pilipenko, S. V., Gottlöber, S., Libeskind, N. I., Yepes, G., Hoffman, Y., 2025, Physical Review D
, 112, 4 , 043515 Published: August 2025
Investigations of trajectories of various objects orbiting the Milky Way (MW) halo with modern precision, achievable in observations by Gaia, requires sophisticated, nonstationary models of the Galactic potential. In this paper we analyze the evolution of the spherical harmonics expansion of MW analogs potential in constrained simulations of the Local Group (LG) from the HESTIA suite. We find that at distances r≥100kpc, the nonspherical part of the potential demonstrates a significant impact of the environment: ignoring the mass distribution outside the virial radius of the MW results in >20% errors in the potential quadrupole at these distances. Account of the environment results in a noticeable change of the angular momenta of objects orbiting MW analogs. Spherical harmonics vary significantly during the last 6 Gyr. We attribute variations of the potential at r≥30kpc to the motions of MW satellites and LG galaxies. We also predict that the nonsphericity of the real MW potential should grow with distance in the range rvir<r<500kpc, since all realizations of simulated MW-like objects demonstrate such a trend.
Rünger, F., Sparre, M., Richter, P., Damle, M., Nuza, S. E., Grand, R. J. J., Hoffman, Y., Libeskind, N., Sorce, J. G., Steinmetz, M., Tempel, E., 2025, Astronomy and Astrophysics
, 700 , A131 Published: August 2025
The accretion and processing of neutral and ionized gas play substantial roles in the evolution of the Milky Way. From the position of the Sun, circumgalactic gas flows in the Milky Way halo are known to span a large range of radial velocities, but the complex kinematics of the circumgalactic medium (CGM) cannot be fully reconstructed from observations because of the blending with foreground interstellar gas in the Milky Way disk. For this paper we used three zoom-in magnetohydrodynamic simulations of the Milky Way and the Local Group from the HESTIA project to systematically investigate the radial velocity distribution of neutral hydrogen (H I) clouds in the CGM in the (simulated) Local Standard of Rest (LSR) velocity frame. Our three simulations, which exhibit substantial differences in their global CGM properties, reveal that 48–65 percent of the extraplanar H I at z > 2 kpc above the plane is confined to a velocity range |vLSR| ≤ 100 km s‑1, implying that the gas is (at least partly) corotating with the underlying disk. In the two most realistic Milky Way realizations, the CGM velocity distribution is skewed toward negative velocities (in particular for H I clouds at vertical distances z > 10 kpc), indicating a net accretion of neutral gas. These results are in line with the statistics from UV absorption-line measurements of the Milky Way CGM, and we also find broad agreement with the Illustris TNG50 simulation. Our study supports a scenario in which a substantial fraction of the Milky Way's CGM resides close to the disk at |vLSR| ≤ 100 km s‑1, where it is hiding from observations as its spectral signatures are covered by foreground interstellar gas features. We furthermore find that 97 percent of the clumps live in the Milky Way halo and are not associated with satellite galaxies. The clumps are magnetized with a magnetic pressure often dominating over the thermal pressure.
Hernández-Martínez, E., Dolag, K., Steinwandel, U. P., Sorce, J. G., Lebeau, T., Aghanim, N., Seidel, B., 2025, arXiv e-prints
, arXiv:2507.15858 Published: July 2025
The intracluster medium (ICM), composed of hot plasma, dominates the baryonic content of galaxy clusters and is primarily observable in X-rays. Its thermodynamic properties, pressure, temperature, entropy, and electron density, offer crucial insight into the physical processes shaping clusters, from accretion and mergers to radiative cooling and feedback. We investigate the thermodynamic properties of galaxy clusters in the Simulating the LOcal Web (SLOW) constrained simulations, which reproduce the observed large-scale structure of the local Universe. We assess how well these simulations reproduce observed ICM profiles and explore the connection between cluster formation history and core classification. Three-dimensional thermodynamic profiles are extracted and compared to deprojected X-ray and Sunyaev - Zel'dovich (SZ) data for local clusters classified as solid cool-core (SCC), weakly cool-core (WCC), and non-cool-core (NCC) systems. We also examine the mass assembly history of the simulated counterparts to link their formation to present-day ICM properties. The simulations reproduce global thermodynamic profiles for clusters such as Perseus, Coma, A85, A119, A1644, A2029, A3158, and A3266. Moreover, they show that CC clusters typically assemble their mass earlier, while NCC systems grow through more extended, late-time merger-driven histories. WCC clusters show intermediate behavior, suggesting an evolutionary transition. Our results demonstrate that constrained simulations provide a powerful tool for linking cluster formation history to present-day ICM properties and point to possible refinements in subgrid physics as well as in resolution that could improve the agreement in cluster core regions.
Arjona-Gálvez, E., Cardona-Barrero, S., Grand, R. J. J., Di Cintio, A., Dalla Vecchia, C., Benavides, J. A., Macciò, A. V., Libeskind, N., Knebe, A., 2025, Astronomy and Astrophysics
, 699 , A301 Published: July 2025
Context. Galaxy sizes are a key parameter to distinguish between different galaxy types and morphologies, which in turn reflect distinct formation and assembly histories. Several methods have been proposed to define the boundaries of galaxies, often relying on light concentration or isophotal densities. However, these approaches are often constrained by observational limitations and do not necessarily provide a clear physical boundary for galaxy outskirts. Aims. With the advent of modern multi-wavelength deep imaging surveys, recent observational studies have introduced a new, physically motivated definition for determining galaxy sizes. This method takes the current or past radial position of the star formation threshold as the size of the galaxy. In practice, a proxy for measuring this position in the present-day Universe is the radial position of the stellar mass density contour at 1 M⊙ pc‑2, defined as R1. In this study, we aim to test the validity of this new definition and assess its consistency across different redshifts and galaxy formation models. Methods. We analysed three state-of-the-art hydrodynamical simulation suites to explore the proposed size-stellar mass relation. For each simulation suite, we examined the stellar surface density profiles across a wide range of stellar masses and redshifts. We measured the galaxy sizes according to this new definition and compared them with the most traditional size metric, the stellar half-mass radius. Results. Our analysis demonstrates that the R1 ‑ M⋆ relation exhibits consistent behaviour across both low and high stellar mass galaxies, with remarkably low scatter. This relation is independent of redshift and holds across the three different cosmological hydrodynamical simulation suites, highlighting its robustness to variations in galaxy formation models. Furthermore, we explore the connection between a galaxy's total mass within R1 and its stellar mass, finding very little scatter in this relation. This suggests that R1 could serve as a reliable observational tracer for a galaxy's dynamical mass. Conclusions. The size-stellar mass relation proposed provides a reliable and physically motivated method of defining the outskirts of galaxies. This method remains consistent not only at z = 0 but also throughout the evolutionary history of galaxies, offering a robust and meaningful framework for galaxy evolution studies.
Böss, L. M., Dolag, K., Steinwandel, U. P., Hernández-Martínez, E., Khabibullin, I., Seidel, B., Sorce, J. G., 2024, Astronomy and Astrophysics
, 692 , A232 Published: December 2024
Aims. Detecting diffuse synchrotron emission from the cosmic web is still a challenge for current radio telescopes. We aim to make predictions about the detectability of cosmic web filaments from simulations. Methods. We present the first cosmological magnetohydrodynamic simulation of a 500 h‑1 c Mpc volume with an on-the-fly spectral cosmic ray (CR) model. This allows us to follow the evolution of populations of CR electrons and protons within every resolution element of the simulation. We modeled CR injection at shocks, while accounting for adiabatic changes to the CR population and high-energy-loss processes of electrons. The synchrotron emission was then calculated from the aged electron population, using the simulated magnetic field, as well as different models for the origin and amplification of magnetic fields. We used constrained initial conditions, which closely resemble the local Universe, and compared the results of the cosmological volume to a zoom-in simulation of the Coma cluster, to study the impact of resolution and turbulent reacceleration of CRs on the results. Results. We find a consistent injection of CRs at accretion shocks onto cosmic web filaments and galaxy clusters. This leads to diffuse emission from filaments of the order Sν ≈ 0.1 μJy beam‑1 for a potential LOFAR observation at 144 MHz, when assuming the most optimistic magnetic field model. The flux can be increased by up to two orders of magnitude for different choices of CR injection parameters. This can bring the flux within a factor of ten of the current limits for direct detection. We find a spectral index of the simulated synchrotron emission from filaments of α ≈ ‑1.0 to –1.5 in the LOFAR band.
