Max Planck Institute for Astrophysics

Abstract The 21 cm line of hydrogen is the most promising probe of the Dark Ages and Cosmic Dawn. We combine hydrodynamical simulations with a large-scale grid in order to calculate the effect of nonlinear structure formation on the large-scale 21 cm power spectrum, focusing on redshifts z = 20–40. As the clumping effect arises from small-scale density fluctuations, it offers a unique opportunity to probe the standard cold dark matter model in a new regime and thus potentially investigate the properties of dark matter. To this end, we also study a warm dark matter–like model with a Gaussian cutoff on a scale of 50 kpc. We find that clumping has a significant impact on the large-scale 21 cm power spectrum, requiring a substantial correction to standard theoretical predictions. For example, for the Dark Ages case at z = 30 and wavenumber k = 0.05 Mpc −1 , small-scale clustering enhances the 21 cm power spectrum by 13%. Once Ly α coupling kicks in due to the first stars, the 21 cm signal strengthens, and the effect of clumping grows; it suppresses the observable power spectrum at z = 20 by 45%, while the warm dark matter–like model has less than half the clumping impact. The clumping effect is significantly higher than the sensitivity of the planned Square Kilometre Array AA ⋆ configuration, by up to a factor of 20 for standard cold dark matter, though detection will require separation from foregrounds and from astrophysical contributions to the 21 cm power spectrum.

Synthesizer is a fast, flexible, modular, and extensible Python package that empowers astronomers to turn theoretical galaxy models into realistic synthetic observations-including spectra, photometry, images, and spectral cubes-with a focus on interchangeable modelling assumptions.By offloading computationally intensive tasks to threaded C++ extensions, Synthesizer delivers both simplicity and speed, enabling rapid forward-modelling workflows without requiring users to manage low-level data processing and computational details.

Abstract The XRISM Resolve X-ray spectrometer makes it possible to gain detailed insights into the gas motions of the intracluster medium (ICM) of galaxy clusters. Current simulation studies focus mainly on statistical comparisons, making the comparison to the currently still small number of clusters difficult due to unknown selection effects. This study aims to bridge this gap, using simulated counterparts of Coma, Virgo, and Perseus from the SLOW constrained simulations. These clusters show excellent agreement in their properties and dynamical state with observations, thus providing an ideal testbed to understand the processes shaping the properties of the ICM. We find that the simulations match the order of the amount of turbulence for the three considered clusters, Coma being the most active, followed by Perseus, while Virgo is very relaxed. Typical turbulent velocities are a few hundred km s −1 , very close to observed values. The resulting turbulent pressure support is ≈1% for Virgo, ≈6% for Perseus, and ≈8% for Coma within the central 1%–2% of R 200 . Compared to previous simulations and observations, measured velocities and turbulent pressure support are on average lower, in line with XRISM findings, thus indicating the importance of selection effects.

Abstract The effect of supernovae (SNe) on star formation in the interstellar medium (ISM) depends sensitively on where SNe explode with respect to ISM clouds. Observationally, SN ISM environments characterized by spatially resolved gas maps can empirically guide the placement of SNe in subgrid models, but unfortunately such measurements remain scarce, as SNe are rare and often distant. Here we demonstrate a new approach—mapping the ISM around evolved massive stars that are soon to explode. These provide a substantially larger sample of “explosion sites” (than just historical SNe) in nearby galaxies that have high-resolution atomic and molecular ISM maps from the Jansky Very Large Array and Atacama Large Millimeter/submillimeter Array. We demonstrate this technique in the well-resolved Local Group spiral M33 by analyzing the 50 pc scale projected ISM densities around red supergiants (RSGs; 8–30 M ⊙ stars) Wolf–Rayet stars (W-Rs; >30 M ⊙ stars), and supernova remnants. We find a mass-dependent correlation between stars and gas clouds, with at least 45% of W-Rs and up to 77% of RSGs having no detectable H 2 at their pixel locations. In the sample with H 2 detections, we find that more-massive younger progenitors are coincident with denser gas. We show that the density distributions for stars >15 M ⊙ are statistically distinct from random alignment of stars and gas in M33. Our work provides the first observationally derived estimate of the fraction of the SN-producing stellar population correlated with ISM density peaks. We demonstrate how this can be compared with galaxy simulations, and advocate similar comparisons to the community for constraining subgrid models.

Abstract Galaxy mergers have long been proposed as a mechanism for funneling gas toward galactic centres, potentially triggering accretion onto supermassive black holes (SMBHs) and igniting active galactic nuclei (AGN). While simulations often support this scenario, observational studies have yielded conflicting results regarding the AGN-merger connection. In this study, we analyze 31 galaxies from cosmological zoom-in simulations spanning redshifts 0.5 < z < 3. We identify mergers using detailed merger trees based on six-dimensional dark matter particle information and identify AGN activity through SMBH accretion histories. To bridge the gap between simulations and observations, we generate mock JWST-like images and extract non-parametric morphological parameters. Employing a k-nearest neighbours (KNN) classifier in a five-dimensional space (four morphological parameters and redshift), we identify mergers in the mock-observed dataset. Our analysis reveals a statistically significant enhancement of AGN activity in merging systems, particularly at lower redshifts (0.5 < z < 0.9), where central gas reservoirs are more depleted. This supports the view that mergers contribute more significantly to AGN triggering in environments with low internal gas reservoirs, while their impact may be less pronounced in gas-rich systems. However, when relying solely on morphological classifications from mock observations, the observed AGN-merger connection weakens, especially at higher redshifts. This underscores the challenges in detecting merger-induced AGN activity observationally and highlights the importance of combining simulations with realistic mock observations to fully understand the AGN-merger relationship.

We present results of field-level inference of the baryon acoustic oscillation (BAO) scale <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msub> <a:mi>r</a:mi> <a:mi>s</a:mi> </a:msub> </a:math> on rest-frame dark matter halo catalogs. Our field-level constraint on <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:msub> <c:mi>r</c:mi> <c:mi>s</c:mi> </c:msub> </c:math> is obtained by explicitly sampling the initial conditions along with the bias and noise parameters via the LEFTfield EFT-based forward model. Comparing with a standard reconstruction pipeline applied to the same data and over the same scales, the field-level constraint on the BAO scale improves by a factor of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mrow> <e:mo>∼</e:mo> <e:mn>1.2</e:mn> <e:mi>–</e:mi> <e:mn>1.4</e:mn> </e:mrow> </e:math> over standard BAO reconstruction. We point to a surprisingly simple source of additional information.

Context. A new class of distinct radio objects, commonly referred to as odd radio circles (ORCs), has been recently discovered. The origin of these features remains unclear because their peculiar properties challenge our current understanding of astrophysical sources for diffuse radio emission. Aims. We test the feasibility and limits of major mergers in galaxy groups as a possible formation channel for ORCs. Methods. By modelling the assembly of a massive galaxy group with a final virial mass of M 200 ∼ 10 13 M ⊙ in a magnetohydrodynamic zoom-in simulation with on-the-fly cosmic ray treatment, we derive the X-ray and radio properties of the system self-consistently and compare them to observations. Results. We show that the X-ray properties of the simulated system agree with characteristics of observed galaxy groups in the relevant mass range, legitimating the comparison between the radio properties of the simulated halo and those of observed ORCs. A major merger between two galaxies in the simulation triggers a series of strong shocks in the circumgalactic medium, which in unison form a ring if the line of sight is perpendicular to the merger axis. The shock is rapidly expands radially and quickly reaches the virial radius of the halo. This formation channel thus readily explains the morphology and large extent of ORCs. However, the inferred radio luminosity of these features is lower than that of observed counterparts, while the degree of polarisation seems systematically over-predicted by the simulation. Conclusions. Fossil cosmic ray populations from active galactic nuclei and stellar feedback might be necessary to explain the full extent of the radio properties of ORCs, since diffusive shock acceleration was the only source term for non-thermal electrons considered in this work.

The Galactic microquasar SS 433 and the radio nebula W50 surrounding it present a prototypical example of a hyper-Eddington binary system shaping its ambient interstellar medium via energetic outflows. In this paper, we present X-ray observations of the SS 433/W50 complex by the eROSITA telescope onboard the SRG space observatory . These data provide images of the entire nebula characterized by a very large dynamic range and allow spectral analysis of the diffuse X-ray emission. ̊m pc of the nebula. These data also allowed us to fully characterize a pair of nearly symmetric, sharp-edged, elongated structures aligned with the orbital axis of the binary system, which lack radio counterparts but are prominent in very-high-energy gamma-ray emission. The resulting multifaceted picture of the interaction between energetic outflows and the surrounding medium paves the way for future focused multiwavelength observations and dedicated numerical simulations.

Many studies in the past few decades have investigated the evolution of young stellar objects based on their spectral energy distribution. This distribution is heavily affected not only by the evolutionary stage, but also by the morphology of the forming star. This study is part of the NEMESIS project, which aims to revisit star formation with the aid of machine-learning techniques and provides the framework for this work. In a first effort toward a novel spectro-morphological classification, we analyzed the morphologies of young stellar objects and linked them to the currently used observational classes. Thereby, we laid the foundation for a spectro-morphological classification and applied the insights learned in this study in a future revisited classification scheme. We obtained archival high-resolution survey images from VISTA for approximately (10,000) young stellar object candidates from the literature toward the Orion star formation complex. Using a self-organizing map algorithm, which is an unsupervised machine-learning method, we created a grid of morphological prototypes from near- and mid-infrared images. Furthermore, we determined the prototypes that best represent the different observational classes we derived from the infrared spectral index via Bayesian inference. We present our grids of morphological prototypes of young stellar objects in the near-infrared. The prototypes were created from observational data alone. They are thus independent of theoretical models. In addition, we show maps that indicate the probability for a prototype to belong to any of the observational classes. Self-organizing maps created from near-infrared images are a useful tool, with limitations, for identifying the characteristic morphologies of young stellar objects in different evolutionary stages. This first step lays the foundation for a spectro-morphological classification of young stellar objects that is to be developed in the future.