arXiv subjects

Marcus Brüggen

Publications and source records attributed to Marcus Brüggen.

At least 19 recordsLinked to original sources

arXiv2026

The Cosmological Simulation Code OpenGadget3 - Implementation of Self-Interacting Dark Matter

Dark matter (DM) could be subject to non-gravitational self-interactions which is relevant to resolve potential problems of cold DM on small scales. Their impact on astrophysical objects such as galaxies and galaxy clusters allows for constraining the strength of this scattering and eventually further properties of the cross-section. To model self-interacting dark matter (SIDM), N-body simulations are a crucial tool widely employed by the SIDM community. In this paper, we describe the SIDM implementation in the cosmological hydrodynamical N-body code OpenGadget3 and release it to the public. It is capable of simulating elastic scattering for various differential cross-sections, including strongly anisotropic cross-sections. Beyond single-species models, the code also allows simulating a two-species model with cross-species interactions. In addition to describing the numerical schemes for modelling various flavours of SIDM, we discuss the technical challenges of implementing them. Moreover, we demonstrate through several test problems that OpenGadget3 can accurately simulate DM self-interactions. Furthermore, we assess the performance of the code and provide scaling tests. Lastly, we highlight remaining challenges in the context of SIDM and describe directions for improving the current state of the art.

astro-ph.IM↗

arXiv2026

Morphology of Radio Sources in Representation Space

Understanding radio source morphologies and their classification remains challenging. We previously developed a deep clustering method based on self-supervised learning to classify a subsample of radio sources from the LOFAR Two-meter Sky Survey DR2. This yielded a labelled subset used to fine-tune an ensemble of classifiers. We aim to identify rare morphological classes in a subsample of LoTSS-DR3, which contains > 13 million sources, beyond the 12 classes previously recognised in the DR2 sample. We further aim to characterise the resulting class distribution. We applied the classifier ensemble to derive class probabilities and representations for our samples. Among DR3 sources with low class probabilities, we searched for new clusters in representation space. Moreover, we use these clusters as centroids to classify the low-probability subset. We found that 88% of the sources fall into clearly separated clusters in representation space, coinciding with the DR2 clusters. Within the remaining sources, we identified representatives of six additional morphological classes, including rare morphologies like winged and FR-ambiguous sources. The number of sources in the resulting 18 classes exhibit a strongly skewed distribution, with four dominant classes constituting 69% of the DR3 sample, while rare morphologies account for only a small fraction. The identification of additional morphological classes shows the possibility of open-set recognition with representation learning in an unexplored dataset. Unlike anomaly detection, which flags individual sources as uncommon, this approach identifies representatives of novel morphological classes, providing a framework for discovering novel source populations. The highly skewed class distribution poses a fundamental challenge for constructing balanced training datasets and highlights the need for open-set approaches in future observations.

astro-ph.IM↗

arXiv2026

Generating radio continuum survey maps of arbitrary size with latent diffusion models

Radio surveys provide exponentially increasing amounts of observational data, which requires the development of novel data reduction and analysis methods. To this end, realistic simulations of observational data provide controlled environments for testing and developing new methods. Diffusion models excel at synthesizing realistic image data, but are limited by size constraints and high computational demands. We implemented a latent diffusion model (LDM) to synthesize realistic radio survey map cutouts. Further, we developed a technique for sampling radio survey maps of arbitrary size with the LDM. This is done by sampling in multiple sequential steps, whereby consistency is provided through context vectors and image inpainting. We trained our model on observations from the LOFAR telescope obtained from the third data release of the LOFAR Two-Metre Sky Survey. We implemented a LDM composed of a vector-quantized variational autoencoder and a diffusion model operating on the resulting latent representations. We added information on source locations, brightness and sizes by extracting parameters from the public source catalog and encoding them into a vector format passed as context to the LDM. We trained the model for image inpainting to facilitate continuous sequential sampling. We were able to generate realistic cutouts of 512 pixel side length, corresponding to ~5.7 arcmin, with precise control over source locations and brightness. Control over source extension was achieved at lower precision. Sampling of arbitrary-sized maps was made possible, showing realistic results with seamless combination of individual samples and limited only by occasional sampling artifacts.

astro-ph.IM↗

arXiv2026

Synchrotron filaments in radio galaxies: rarity, stability, and environmental influences from LOFAR and ROSAT observations

We present a systematic investigation of filamentary synchrotron structures in radio galaxies, using deep 144 MHz observations from the LOFAR Two-Metre Sky Survey (LoTSS) in combination with archival ROSAT X-ray data. These narrow, collimated features, linking radio lobes and often aligned with jet axes, are rare: our visual inspection of 548 cluster-associated sources identified 12 candidates (~2.2%), of which three exhibit clearly resolved filaments suitable for detailed X-ray and synchrotron minimum pressure analysis. Minimum pressures in these filaments are consistently lower than the ambient thermal pressure derived from X-ray measurements. This disparity implies a role for external confinement in filament stability, aligning with theoretical predictions of thermal pressure support and potentially toroidal magnetic field configurations. We discuss filament formation scenarios, including relic AGN outflows, magnetic draping, and plasma instabilities. Our findings highlight the utility of filamentary structures as probes of intracluster magnetic field topology and AGN feedback, and demonstrate the need for high-resolution, multi-frequency studies to constrain their origin and evolution.

astro-ph.GA↗

arXiv2026

Probing Variations in Earth's Ionosphere Using Pulsars

We present high cadence 10-minute rotation measure (RM) monitoring of PSR~J0814+7429 using the LOw-Frequency ARray, aiming to probe ionospheric variability along the pulsar line of sight (LoS). By separating the ionospheric contribution from the observed RM, we quantitatively reconstruct the diurnal variation of the ionospheric electron density along the pulsar LoS based on the World Magnetic Model. The derived variations exhibit clear solar-driven modulation, including the ionospheric noontime bite-out phenomenon, and show good agreement with the LoS total electron content reconstructed from independent global vertical total electron content maps. These results demonstrate the feasibility of using pulsars as probes of temporal variations in the electron density of the Earth's ionosphere.

astro-ph.HE↗

arXiv2026

Supersonic Motion in the Driving Region of M82

The prototypical starburst galaxy M82 is host to an expansive, multiphase outflow whose driving mechanism is not fully understood. Longstanding models suggest that energy and mass injection from supernova into the hottest phase of the galactic wind could drive the cooler phases, but validating these models has been difficult due to the lack of constraints on the hot wind energetics. The high-resolution spectral capabilities of XRISM have generated the tightest constraints to date on the temperatures of the hot wind, as well as the first direct measurement of its velocity dispersion. In this work, we use these new observational constraints to test a model of a supernova-driven free wind. We generate a suite of highly idealized hydrodynamic simulations varying the energy and mass loading of the starburst and construct mock spectra to compare against the XRISM results. We find that the observed velocity dispersion is impossible to replicate using our free-wind model alone, and extra broadening is required to fit the spectrum. We interpret this broadening to be due not to bulk outflow, but rather to smaller scale non-thermal motions in the driving region of the starburst. This implies supersonic motion (Mach 1.71-3.14) of the hot gas in the central region of the galaxy. As supersonic motions are unexpected, it is possible that a significant amount of the energy that should go into heating the gas is instead going towards other sources such as amplifying magnetic fields and driving cosmic rays.

astro-ph.GA↗

arXiv2026

AGN Jets from Formation to Dissipation

Active Galactic Nuclei (AGN) are among the most energetic phenomena in the Universe, capable of launching powerful relativistic jets that extend from sub-parsec to megaparsec scales. These jets play a crucial role in regulating star formation, redistributing energy and matter, and shaping the evolution of galaxies and their environments. Despite decades of study, a comprehensive understanding of how AGN jets form, propagate, and dissipate remains elusive. The aim of this chapter is to highlight how the future capabilities of the the Square Kilometre Array (SKA), as a standalone array as well as in combination with Very Long Baseline Interferometry (VLBI) arrays and multi-wavelength facilities, will transform our capabilities to study the co-evolution of AGN jets and their host galaxies from jet formation to dissipation scales.

astro-ph.GA↗

arXiv2026

The Cosmic Ray Life Cycle in Galaxy Clusters

Within the cosmic web, gravitational energy, linked to the formation and growth of the Universe's largest structures and the activity of active galactic nuclei (AGN), is converted to heat through processes such as turbulence and shock waves. These processes have a fundamental impact on the evolution of galaxy clusters. For example, they lead to the amplification of magnetic fields and the production of cosmic ray (CR) electrons that emit continuum radio waves via synchrotron emission. This produces sources on scales of the entire hosting clusters. These large radio sources in galaxy clusters are often classified based on their morphological appearance as radio halos, cluster radio shocks (radio relics), and other types. To understand the CR acceleration processes in galaxy clusters (and beyond), and to gain a comprehensive view of these sources, including their long-term interactions, SKA telescope should conduct both deep observations of a carefully selected sample of nearby clusters as well as shallower wide-area surveys. Thanks to their capabilities - in particular the sensitivity to polarised and low-frequency emission - SKA-Mid (Bands 1 and 2) and SKA-Low are ideally suited to probing magnetic field structures in galaxy clusters, as well as the large reservoir of low-energy CRs that may be accelerated by yet-unexplored microphysical mechanisms. The high sensitivity to low-frequency emission will also be fundamental to detect the long term actions and interactions of these phenomena over gigayear timescales.

astro-ph.CO↗

arXiv2026

Bulk and turbulent gas motions in the interacting galaxy cluster Abell 3395 South observed with XRISM

We investigate the gas motions in the core region of the Abell~3395 South subcluster (A3395S) using high-resolution X-ray spectroscopy with XRISM/Resolve. By analyzing the Fe~XXV He$α$ emission line, we directly measure the line-of-sight bulk and turbulent velocities of the intracluster medium. We find that the one-dimensional turbulent velocity is low, at the level of $124\pm21~{\rm km\,s^{-1}}$, while a significant line-of-sight bulk velocity of $263\pm23~{\rm km\,s^{-1}}$ is detected. The coexistence of low turbulence and finite bulk motion suggests that A3395S has not yet reached a dynamically relaxed state. These results are consistent with the non-detection of a radio halo in A3395S, implying that turbulent particle reacceleration is currently inefficient in the cluster core. This study demonstrates that high-resolution X-ray spectroscopy with XRISM provides a powerful means to directly constrain intracluster medium dynamics in merging galaxy clusters, and it provides a reference for future comparative studies of A3395N and A3391 within the same large-scale structure.

astro-ph.CO↗

arXiv2026

Inverse energy transfer in decaying MHD turbulence: A shell-to-shell analysis

In decaying magnetohydrodynamic turbulence, energy can be transported from small to large scales, known as inverse transfer. We explore the mechanism behind this phenomenon using shell-to-shell transfer functions. Independent of magnetic net-helicity, large magnetic scales receive energy directly from the integral scale in both the magnetic and kinetic reservoirs, leading to increasingly non-local transfer for larger receiving scales. The resulting rate of energy increase in each receiving scale is proportional to its energy, resulting in self-similar, multiplicative growth. Even though the system is magnetically dominated, contributions from kinetic-magnetic and magnetic-magnetic energy-exchange are similar in magnitude. In the case of vanishing net-helicity, transfer functions between the positively and negatively helical parts of the field are computed. We find that inverse transfer only occurs within each helical sector, not across them. Our findings are consistent with the theory underlying the conservation of the Hosking integral, which explains inverse transfer as merging of local magnetic islands with equal-signed helicity.

physics.plasm-ph↗

arXiv2026

Pulsar scintillation studies with LOFAR III. Annual variations in PSR~J0814$+$7429

The interstellar scintillation observed in radio pulsars arises from interference between electromagnetic waves scattered by electron density fluctuations in the turbulent interstellar plasma, providing a critical tool for probing the small-scale structure of the ionized interstellar medium and the pulsar system itself. The primary aim of this work is to study long-term scintillation variations for a bright and nearby pulsar, PSR J0814$+$7429, carried out from 2013 September to 2023 September with the LOw-Frequency ARray (LOFAR) High Band Antennae in the frequency range of 120 - 170 MHz. We derive the basic scintillation parameters, scintillation bandwidth ($Δν_{\rm d}$) and scintillation timescale ($Δτ_{\rm d}$), from the two-dimensional (2D) auto-covariance function of the dynamic spectra that are a 2D matrix of pulse intensity as a function of time and frequency. We present the long-term monitoring of $Δν_{\rm d}$ and $Δτ_{\rm d}$ for PSR J0814$+7429$, which shows a strong annual variation in the time series of the $Δτ_{\rm d}$. From our modeling of the annual variations of scintillation velocities, the scattering screen is anisotropic and located at $0.23\pm0.02$ kpc from the Earth, likely corresponding to the boundary of the Local Bubble.

astro-ph.HE↗

arXiv2026

Zooming in on the circumgalactic medium with GIBLE: Cloud-scale simulations with cosmological initial conditions

We conduct simulations of $\sim$kpc-scale cool clouds in the circumgalactic medium (CGM), using initial conditions sampled from a highly resolved cosmological magneto-hydrodynamical zoom-in of a Milky Way-like galaxy. We select ten distinct cold clouds with masses of $m_{\rm{cloud}}$ $\sim$ $10^{4.5-5}$ M$_\odot$, originally resolved at a mass resolution of $m_{\rm{gas}}$ $\sim$ $200$ M$_\odot$. To further resolve small-scale features and physics, we implement a targeted refinement scheme within spherical regions co-moving with each cloud, thereby boosting the local mass resolution by a factor of 1000, reaching $m_{\rm{gas}}$ $\sim$ $0.2$ M$_\odot$ (spatial resolution, $r_{\rm{gas,cloud}}$ $\sim$ $O(\rm{pc})$). The selected clouds have diverse properties, across a broad parameter space, resulting in heterogeneous evolution. For the clouds we study, radiative cooling is the dominant physical process enabling cloud survival, while magnetic fields play a comparatively smaller role. The motion of these clouds is governed not only by drag forces that decelerate them, but also by acceleration from momentum exchange with the complex background velocity field, which can cause them to move faster than ballistic projectiles set by their initial velocities. Our results suggest that the non-trivial details of realistic cosmological initial conditions -- specifically the complex density, temperature, and velocity fields -- may play an important role in subsequent cloud evolution, and that sampling the output of an existing large-scale simulation provides a self-consistent approach to capture these effects without ad hoc assumptions.

astro-ph.GA↗

arXiv2026

Towards FAIR Astrophysical Simulations

Reproducibility is a cornerstone of science. FAIR (findable, accessible, interoperable, and reusable) data is often a vital step towards testing the reproducibility of results. The implementation of FAIR principles in the astrophysical simulation community is still varied. We approach the discussion of this topic mainly from a high-performance computing (HPC) point of view. We identify the main obstacles to FAIR astrophysics simulations: First, the vast datasets created in simulations on HPC facilities complicate FAIR data management. Second, missing incentives to fully share codes, results, and diagnostic data. Third, a lack of workflows that include data publication and technical support. Therefore, particularly smaller research groups struggle due to the unavailability of dedicated personnel and time in their efforts towards FAIR and open simulations. We propose actionable steps towards achieving ``FAIRer'' data and open source publication standards in numerical astrophysics. Our suggestions include low-threshold methods to fulfil the basic FAIR requirements as well as basic tools for FAIR (meta-)data generation and data/code publication. This work is a high-level overview intended to initiate discussions within the community, offering initial solutions to these challenges.

astro-ph.IM↗

arXiv2026

The life of central radio galaxies in clusters: AGN-ICM studies of eRASS1 clusters in the ASKAP fields

The mechanical feedback from the central AGNs can be crucial for balancing the radiative cooling of the intracluster medium at the cluster centre. We aim to understand the relationship between the power of AGN feedback and the cooling of gas in the centres of galaxy clusters by correlating the radio properties of the brightest cluster galaxies (BCGs) with the X-ray properties of their host clusters. We used catalogues from the first SRG/eROSITA All-Sky Survey (eRASS1) along with ASKAP radio data. In total, we identified 134 radio sources associated with BCGs of the 151 eRASS1 clusters located in the PS1, PS2, and SWAG-X ASKAP fields. Non-detections were treated as upper limits. We correlated BCG radio luminosity, largest linear size (LLS), and BCG offset with the integrated X-ray luminosity of their host clusters. To characterise cool cores (CCs) and non-cool cores (NCCs), we used the concentration parameter $c_{R_{500}}$ and combined it with the BCG offset to assess cluster dynamical state. We analysed the correlation between radio mechanical power and X-ray luminosity within the CC subsample. We observe a potential positive trend between LLS and BCG offset, suggesting an environmental effect on radio-source morphology. We find a weak trend where more luminous central radio galaxies are found in clusters with higher X-ray luminosity. Within the CC subsample, there is a positive but highly scattered relationship between the mechanical luminosity of AGN jets and the X-ray cooling luminosity. This finding is supported by bootstrap resampling and flux-flux analyses. The correlation indicates that AGN feedback is ineffective in high-luminosity (high-mass) clusters. At a cooling luminosity of $L_{\mathrm{X},~r<R_\mathrm{cool}}\approx 5.50\times10^{43}$ erg/s, on average, AGN feedback appears to contribute only about 13%-22% of the energy needed to offset the radiative losses in the ICM.

astro-ph.CO↗

arXiv2026

An Improved Fit to the Density Distribution in Supersonic Isothermal Turbulence

The density distribution of supersonic isothermal turbulence plays a critical role in many astrophysical systems. It is commonly approximated by a lognormal distribution with a variance of $σ_{s,{\rm V}}^2 \approx \ln(1 + b^2 M_{\rm V}^2),$ where $s \equiv \ln ρ/ρ_0,$ $M_{\rm V}$ is the rms volume-weighted Mach number, and $b$ is a parameter that depends on the driving mechanism, which can be solenoidal (divergence-free), compressive (curl-free), or a mix of both. However, this fit neglects the driving correlation time, $τ_{\rm a}$, which plays a key role when compressive driving is significant. Here we conduct turbulence simulations spanning a wide range of Mach numbers, driving mechanisms, and $τ_{\rm a}$ values. In the compressive case, $σ_{s,{\rm V}}^2$ is not well fit by the standard expression. Instead, it scales approximately linearly with $M_{\rm V},$ and its dependence on $τ_{\rm a}$ is $σ_{s,{\rm V}}^2 \approx M_{\rm V} [1 + \frac{2}{3}(1 + λ_{\rm a})Θ(1 + λ_{\rm a})]$, where $λ_{\rm a} \equiv \ln(τ_{\rm a}/τ_{\rm e})$, $τ_{\rm e}$ is the eddy turnover time, and $Θ$ is the Heaviside step function. Mixed-driven turbulence shows a weak dependence on $τ_{\rm a},$ and for solenoidally-driven turbulence, $σ_{s,{\rm V}}^2 \approx \frac{1}{3}M_{\rm V}$, which is consistent with the standard expression when $M_{\rm V} \lesssim 8.$ The volume-weighted mean and skewness also show systematic trends with $M_{\rm V}$ and $τ_{\rm a}$, deviating from lognormal expectations. The mass-weighted density distribution displays significant broadening and skewness in compressively-driven cases, especially at large $τ_{\rm a}/τ_{\rm e}$. These results provide a refined framework for modeling astrophysical turbulence.

astro-ph.GA↗

arXiv2025

On the kinematic and thermodynamic state of clouds in complex wind-multi-cloud environments using a Friends-of-Friends analysis

We investigate the interaction between a shock-driven hot wind and a cold multi-cloud layer, for conditions commonly found in interstellar and circumgalactic gas. We present a method for identifying distinct clouds using a Friends-of-Friends algorithm. This approach unveils novel detailed information about individual clouds and their collective behaviour. By tracing the evolution of individual clouds, our method provides comprehensive descriptions of cloud morphology, including measures of the elongation and fractal dimension. Combining the kinematics and morphology of clouds, we refine previous models for drag and entrainment processes. Our by-cloud analysis allows to discern the dominant entrainment processes at different times. We find that after the initial shock passage, momentum transfer due to condensation becomes increasingly important, compared to ram pressure, which dominates at early times. We also find that internal motions within clouds act as an effective dynamic pressure that exceeds the thermal pressure by an order of magnitude. Our analysis shows how the highly efficient cooling of the warm mixed gas at temperatures $\sim 10^{5}$ K is effectively balanced by the kinetic energy injected by the hot wind into the warm and cold phases via shocks and shear motions. Compression-driven condensation and turbulence dissipation maintain a multi-phase outflow and can help explain the presence of dense gas in galaxy-scale winds. Finally, we show that applying our Friends-of-Friends analysis to $\rm{H}_\rm{I}$-emitting gas and correcting for beam size and telescope sensitivity can explain two populations of $\rm{H}_\rm{I}$ clouds within the Milky-Way nuclear wind as structures pertaining to the same outflow.

astro-ph.GA↗

arXiv2025

The MeerKAT Galaxy Cluster Legacy Survey -- II. Catalogue of the diffuse radio emission in MeerKAT-GCLS clusters

We present a follow-up study focused on cluster-scale diffuse radio emissions in 115 galaxy clusters in the Southern sky, using full-resolution (7.8") and tapered low-resolution (15") images from the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). In this MGCLS follow-up paper, we update and quantitatively characterise the presence of diffuse radio emission and provide detailed catalogue information on its radio properties at 1.28 GHz. As the MGCLS sample is heterogeneous and was initially used as a test bed to reveal the scientific potential of MeerKAT, the reported numbers are subject to this special case. More than half ($\sim$54%; 62/115) of the observed MGCLS clusters present diffuse cluster radio emission, with the total number of diffuse radio sources or candidates detected being 103. Including candidates, we find that radio relics are the most frequently detected diffuse sources in MGCLS at 53% (55/103), followed by halos at 32% (33/103) and mini-halos at 10% (11/103), with only 3% (3/103) being Phoenixes. The sizes of the diffuse radio structures and candidates range from 55 kpc to over 2 Mpc, with $P_{1.28GHz}$ radio power ranging from $10^{22}$ W Hz$^{-1}$ to greater than $10^{25}$ W Hz$^{-1}$. In-band radio spectral index estimates reveal revived radio plasma emissions that exhibit steep radio spectral indices down to $α^{1656}_{908} \sim -3.5$. Mini-halos and their respective candidates are detected mainly in low-mass ($M_{500}$ $\leq$ 5$\times10^{14}$ M$_\odot$) and low-power ($P_{1.4GHz}$ $\leq$ $10^{23}$ W Hz$^{-1}$) systems. We suggest the presence of a statistically significant correlation between the 1.4 GHz radio power and the cluster mass for mini-halo (and candidate) systems.

astro-ph.GA↗

arXiv2025

The XMAGNET exascale MHD simulations of SMBH feedback in galaxy groups and clusters: Overview and preliminary cluster results

We present initial results from extremely well-resolved 3D magnetohydrodynamical simulations of idealized galaxy clusters, conducted using the AthenaPK code on the Frontier exascale supercomputer. These simulations explore the self-regulation of galaxy groups and cool-core clusters by cold gas-triggered active galactic nucleus (AGN) feedback incorporating magnetized kinetic jets. Our simulation campaign includes simulations of galaxy groups and clusters with a range of masses and intragroup and intracluster medium properties. In this paper we present results that focus on a Perseus-like cluster. We find that the simulated clusters are self-regulating, with the cluster cores staying at a roughly constant thermodynamic state and AGN jet power staying at physically reasonable values ($\simeq 10^{44}-10^{45}$~erg/s) for billions of years without a discernible duty cycle. These simulations also produce significant amounts of cold gas, with calculations having strong magnetic fields generally both promoting cold gas formation and allowing cold gas out to much larger clustercentric radii ($\simeq 100$~kpc) than simulations with weak or no fields ($\simeq 10$~kpc), and also having more filamentary cold gas morphology. We find that AGN feedback significantly increases the strength of magnetic fields at the center of the cluster. We also find that the magnetized turbulence generated by the AGN results in turbulence where the velocity power spectra are tied to AGN activity whereas the magnetic energy spectra are much less impacted after reaching a stationary state.

astro-ph.GA↗