We present a velocity-resolved three-dimensional map of local atomic hydrogen (HI) within 1.25 kpc of the Sun, tackling the challenge of converting emission from position-position-velocity space into true 3D structure. Our method combines the HI4PI full-sky survey with the Edenhofer et al. (2024) 3D dust map in the framework of Information Field Theory, enabling a joint reconstruction of the local HI density, radial velocity field, and effective line width while also separating emission arising inside the mapped local volume from more distant Galactic HI. The inference is driven by morphological matching between dust and HI structures together with kinematic coherence in 3D space. Synthetic data tests show that the method recovers the local density and velocity structure, even in the presence of substantial contamination from distant emission. The resulting map reveals a smoother, more diffuse local HI distribution than the dust, a declining HI-to-dust ratio toward high dust column densities consistent with the atomic-to-molecular transition, and a velocity field that captures both large-scale Galactic rotation and local non-circular velocities. Independent comparisons with maser and young stellar cluster velocities agree with the recovered kinematics. This HI map provides a new three-dimensional, kinematically resolved view of the nearby atomic interstellar medium and a foundation for localising other velocity-resolved Galactic emission in physical space.

We analyse the neutral ISM of galaxies at redshift z=0 in the COLIBRE hydrodynamical simulations and investigate the conditions under which these two gas phases coexist in a narrow range of thermal pressures. COLIBRE galaxies are selected based on the metallicity of their ISM. The median and mass-weighted distributions of thermal pressures of the multiphase ISM are analysed and compared to thermal equilibrium models and observations. The ISM in galaxies with gas metallicities similar to solar values exhibits a clear multiphase structure with a warm and cold phase coexisting in a certain range of thermal pressures. The pressures at which the ISM is multiphase depend on the gas metallicity. For COLIBRE galaxies with lower metallicities (Z_ISM≲0.1 Z_⊙), this multiphase structure largely disappears, partly due to resolution. The thermal pressures weighted by the HI mass of the neutral phases in COLIBRE galaxies are lower than, but still comparable to, some theoretical works and observational estimates. The thermal pressures show a strong dependence on the weighting scheme. If weighted by the star formation rate or CI mass, the thermal pressures of the cold phase match those derived from observations. The resulting pressures depend on a combination of the assumed radiation field strength, dust abundance, limited resolution and the weighting scheme. The strong dependence of the thermal pressures on the weighting scheme indicates observational tracers used to estimate the thermal pressure are biased towards high-pressure regions.

We present first results from SIMPLIFI (Study of Interstellar Magnetic Polarization: a Legacy Investigation of Filaments), a SOFIA/HAWC+ 214 mu m polarimetric survey of Galactic molecular cloud filaments. We trace magnetic field morphology from the DR21 Main Ridge into surrounding subfilaments at similar to 0.1 pc resolution, extending polarimetric detections for the first time beyond high-column-density regions probed by prior submillimeter observations. We compare the plane-of-sky orientations of the magnetic field, B-pos , the projected gravitational acceleration, g(pos) , and the intensity gradient rotated by 90 degrees, del I-perpendicular to . The relative orientation of Bpos and del I-perpendicular to transitions from preferentially parallel in subfilaments to perpendicular in the DR21 Main Ridge at N(H-2) similar to 2 & times; 10(22) cm(-2), consistent with thresholds seen with Planck and expected in clouds formed from strongly magnetized, sub-Alfv & eacute;nic, magnetically subcritical gas ( M-A less than or similar to 1 , M/Phi(B)<[M/Phi(B)](cr) ). We find that the relative alignment between orientations shows region-to-region and pixel-to-pixel variations at fixed column density. Column density alone is thus not sufficient to encode changes in magnetic field structure. Theoretical models must account for additional drivers. Our central finding is that g(pos) and B-pos remain aligned throughout the cloud regardless of column density or environment, unlike the environment-dependent behavior of B-pos versus del I-perpendicular to and gpos versus del I-perpendicular to . This persistent alignment is consistent with magnetically guided accretion: subfilaments channel material along field lines at several 10(-3) M circle dot yr(-1), sufficient to assemble the Ridge within similar to 10(6) yr and sustain high-mass star formation. This framework also explains why observed radial velocities (approximate to 2 km s(-1)) fall well below freefall expectations (approximate to 8 km s(-1)): with the field nearly in the plane of the sky, only a small fraction of the accretion velocity projects along the line of sight.

Context. Turbulence plays an important role in shaping the interstellar medium, and it strongly influences star formation. Aims. We aim to identify the physical processes capable of sustaining H I turbulence in the solar neighborhood. Methods. We compare recent H I line-of-sight velocity observations within a volume of radius 70–500 pc centered on the Sun with a suite of 1 kpc numerical simulations that include two distinct turbulent drivers: (i) supernova (SN) feedback and (ii) imposed large-scale turbulent forcing. For each simulation, we constructed synthetic sky maps that closely mimic the observational one, allowing for a consistent comparison between the simulations and the observational data. Results. The H I observations show a median velocity dispersion of 11.1 km s−1 in the solar neighborhood. The SN-driven simulations systematically underpredict this value, yielding dispersions in the range 4.9–6.7 km s−1. We find that the simulations with strong enough large-scale forcing can reproduce not only the median observed velocity dispersion but also the observed velocity distribution.

The Local Bubble (LB) is a hot, low-density cavity in the solar neighborhood, inside which the Solar System is currently located. The X-ray emission from such bubbles is strongly governed by the gas density, temperature, and the effects of line-of-sight column density. Yet the physical processes that control the formation and evolution of this emission remain incompletely understood. We analyze a LB analogue identified within a magnetohydrodynamical simulation to investigate the key physical factors that shape its X-ray properties. In post-processing, we examine the spatial distribution, variability, and observational constraints of the X-ray emission. Our study reveals three main results: (1) Shortly after a supernova (SN), the bulk of the X-ray emission arises from a small fraction of the bubble's volume, concentrated in hot regions around recent SN sites. Approximately 95

Numerical simulations provide a unique opportunity to improve our understanding of the role of magnetic fields in the interstellar medium of galaxies and in star formation. However, many existing galaxy-scale numerical simulations impose a Kennicutt-Schmidt (KS) star formation law by construction. In this paper, we present two AREPO simulations of an isolated star-forming galaxy with and without magnetic fields, using sink particles to model star formation without imposing a KS relation. We examine global differences between the models and investigate the impacts on star formation. We include a time-dependent, non-equilibrium chemical network coupled to a thermal evolution scheme and supernova feedback. Our magnetic field amplifies via dynamo action from a small initial seed field. We find a more compact magnetohydrodynamic (MHD) disc (radius similar to 5.1 kpc, compared to similar to 7.4 kpc), with a diffuse atomic envelope above and below the plane that is not seen in the hydrodynamic (HD) case. The HD disc displays a smoother, more even radial distribution of gas and star formation, and more bubbly substructure. Our MHD simulation has a higher proportion of dense, gravitationally unbound gas than the HD case, but a lower star formation rate, an average between 125 and 150 Myr of similar to 4.8 M-circle dot yr compared to similar to 8.4 M-circle dot yr(1). We see a clear shift in the KS relation to higher gas surface densities in the MHD case, more consistent with observations. The additional magnetic support against gravitational collapse seems to raise the threshold gas surface density required for star formation.

The relationship between magnetic field strength and gas density is essential to understand the interstellar medium and star formation. Zeeman measurements in dense atomic and molecular gas phases have traditionally been used to directly probe magnetic field strengths in the Milky Way. This allowed derivation of a relationship between magnetic field strength B and gas number density n. We recently generalized this relation as a two-part power-law with non-zero slopes and a transition density given as B/B_0 ∝ (n/n_0)^α_1 for n ≤ n_0 and (n/n_0)^α_2 for n > n_0. Here, we extend our previous hierarchical Bayesian framework by incorporating a large body of pulsar observations that probe the diffuse interstellar medium and explicitly modelling density uncertainties through a global log-density correction parameter R applied to all densities. We also account for magnetic field geometry and measurement uncertainties through a magnetic hyperparameter to estimate B. This results in a stronger constraint on the diffuse gas part of the B–n relation. Our results confirm a non-zero exponent in the diffuse gas and a broad transition density with our best model and data set yielding maximum a posteriori results of α_1 = 0.18^+0.02_-0.02, α_2 = 0.63^+0.08_-0.05, n_0 = 1630^+2560_-1430 cm^-3, and B_0 = 7.60^+2.00_-3.47 μG.

The fragmentation properties of parsec- scale clumps play a fundamental role in shaping the dense gas condensations known as cores, the immediate progenitor of stars. The distribution of core masses, the so-called core mass function, is the precursor of the stellar initial mass function, which governs the distribution of stellar masses and, consequently, the evolution of galaxies. The stellar initial mass function is often described by a typical Salpeter-like slope, although deviations toward more top-heavy distributions have been reported in extreme environments, raising questions about its universality and about the physical connection between the two mass functions. To date, there are no observational constraints on the core mass function and its link to the initial mass function beyond the Milky Way.Here we present a study of the fragmentation properties and the measurement of the core mass function in an external galaxy, focusing on the 30Dor-10 region in the Large Magellanic Cloud, using high resolution observations that probe spatial scales down to 2000 au. Robust statistical analysis demonstrates that the core mass function is consistent with a Salpeter-like slope and suggests that variations in the stellar mass distribution arise from evolutionary processes rather than from initial fragmentation.

The Milky Way is a complex ecosystem. We can obtain detailed observations of it by probing the physical mechanisms that determine its interstellar medium. For a detailed comparison with observations and to provide theories for missing observables, the Milky Way must be modelled as accurately as possible. However, details of the Galactic structure are not fully defined by observations, which raises the need for more generalised models. With the Rhea simulations, we present a set of Milky Way-like simulations containing detailed physics of the interstellar medium as well as star formation and stellar feedback. We conducted two simulations that differ in the gravitational potential: one fitted to several structural details derived from observations and another that only reproduces the most basic quantities. We find little difference in the overall morphology except for the bar region, which funnels gas towards the Galactic inner region and therefore prevents quenching in the centre. Despite differences with galacto-centric radius, the global star formation rate is almost identical in both setups. A spiral arm potential does not influence properties of groups of formed stars. A bar potential, however, reduces the size and formation time of those associations. We conclude that a spiral arm potential has little influence on star formation in the Galaxy, except for producing long-lived spiral structures instead of transient ones, and that a galactic bar potential has a noticeable influence on star formation, mainly within the innermost 2.5 kpc.

Context. The physical mechanisms that regulate the collapse of high-mass parsec-scale clumps and allow them to form clusters of new stars, including high-mass stars, represent a crucial aspect of star formation. Aims. To investigate these mechanisms, we developed the Rosetta Stone project: an end-to-end (simulations double left right arrow observations) framework that is based on the systematic production of realistic synthetic observations of clump fragmentation and their subsequent comparison with real data. Methods. In this work, we compare ALMA 1.3 mm continuum dust emission observations from the Star formation in QUiescent And Luminous Objects (SQUALO) survey with a new set of 24 radiative magnetohydrodynamical (RMHD) simulations of high-mass clump fragmentation, post-processed using the CASA software to mimic the observing strategy of SQUALO (combining ACA and 12 m array). The simulations were initialized combining typical values of clump mass (500 and 1000 M circle dot) and radius (similar to 0.4 pc) with two levels of turbulence (Mach number, M, of 7 and 10) and three levels of magnetization (normalized mass-to-magnetic-flux ratio, mu, of similar to 3, 10, and 100). Following the clump evolution over time with two initial random seeds projected along three orthogonal directions, we produced a collection of 732 synthetic fields. On each field, we performed source extraction and photometry using the Hyper software, as in the SQUALO project, to quantitatively characterize how the initial conditions of the clump and the environment affect the observed fragmentation properties. Results. The synthetic observations of clump fragmentation at similar to 7000 AU resolution revealed between 2 and 14 fragments per field, indicating a complex fragmentation process. Among the initial conditions of the simulations, magnetic fields have the largest impact on the fragment multiplicity at these scales. In advanced stages of clump evolution, a lower number of fragments is preferentially associated with magnetized clumps. The clump magnetization might also affect the clustering of fragments, favoring more tightly bound distributions when the magnetic field is stronger. Fragments identified at similar to 7000 AU correspond to individual or multiple sink particles in similar to 75% of the cases. This result suggests that not all identified fragments are actively forming stars. Both sink particles and fragments accrete mass throughout the whole clump evolution. This evidence favors a scenario in which fragments are not isolated from the environment and is thus consistent with results from the SQUALO survey. Conclusions. Our study demonstrates the importance of synthetic observations in interpreting results from interferometric observations.

We present a reconstruction of the line-of-sight motions of the local interstellar medium (ISM) based on the combination of a model of the three-dimensional dust density distribution within 1.25,kpc from the Sun and the i and CO line emission within Galactic latitudes $|b|$,≤,5 We used the histogram of oriented gradient (HOG) method, a computer vision technique for evaluating the morphological correlation between images, to match the plane-of-the-sky dust distribution across distances with the atomic and molecular line emission. We identified a significant correlation between the 3D dust model and the line emission. We employed this correlation to assign line-of-sight velocities to the dust across density channels and produce a face-on map of the local ISM radial motions with respect to the local standard of rest (LSR). We find that most of the material in the 3D dust model follows the large-scale pattern of Galactic rotation; however, we also report local departures from the rotation pattern with standard deviations of and for the i and CO line emission, respectively. The mean kinetic energy densities corresponding to these streaming motions are around and from either gas tracer. Assuming homogeneity and isotropy in the velocity field, these values are within a factor of a few of the total kinetic energy density. These kinetic energy values are roughly comparable to other energy densities, thus confirming the near-equipartition in the local ISM. Yet, we identify energy and momentum overdensities of around a factor of ten concentrated in the Radcliffe Wave, the Split, and other local density structures. Although we do not find evidence of the local spiral arm's impact on these energy overdensities, their distribution suggests the influence of large-scale effects that, in addition to supernova feedback, shape the energy distribution and dynamics in the solar neighborhood.

The PRIMAger instrument on board the proposed PRIMA satellite will offer the unprecedented capability to obtain hundreds of square-degree maps in polarized emission at sub-arcminute resolution in four Far-IR bands. This will open a unique window to study magnetic fields in our Galaxy. PRIMAGAL, a proposed survey of polarized dust emission in the Milky Way Galactic Plane will determine the strength and orientation of magnetic fields toward several thousands of filamentary clouds in a wide range of linear masses, column densities, evolution, star-formation rates and efficiencies, and Galactic environment. We will address for the first time in a statistically significant fashion the role that magnetic fields play in shaping the formation, evolution, and fragmentation of dense ISM filaments down to a minimum scale of 0.4 pc up to 8 kpc distance from the Sun. A 4-band polarization survey of the Galactic Plane with |b|<= 1 (a total of 720 sq. deg.) can be executed by PRIMAger in similar to 1200 h including all mapping and instrument overhead. (c) 2025 Society of Photo-Optical Instrumentation Engineers (SPIE)

Turbulence in the interstellar medium (ISM) plays an important role in many physical processes, including forming stars and shaping complex ISM structures. In this work, we investigate the H i turbulence properties of the Small Magellanic Cloud (SMC) to reveal what physical mechanisms drive the turbulence and at what scales. Using high-resolution H i data from the Galactic ASKAP survey and multipoint structure functions (SFs), we perform a statistical analysis of H i turbulence in 34 subregions of the SMC. The two-point SFs tend to show a linear trend, and their slope values are relatively uniform across the SMC, suggesting that large-scale structures exist and are dominant in the two-point SFs. On the other hand, seven-point SFs enable us to probe small-scale turbulence by removing large-scale fluctuations, which is difficult to achieve with the two-point SFs. In the seven-point SFs, we find break features at scales of 34–84 pc, with a median scale of ∼50 pc. This result indicates the presence of small-scale turbulence fluctuations in the SMC and quantifies their scale. In addition, we find strong correlations between the slope values of the seven-point SFs and stellar-feedback-related quantities (e.g., H α intensity, the number of young stellar objects, and the number of H i shells), suggesting that stellar feedback may affect the small-scale turbulence properties of the H i gas in the SMC. Lastly, the estimated sonic Mach numbers across the SMC are subsonic, which is consistent with the fact that the H i gas of the SMC primarily consists of a warm neutral medium.

Context. Star formation and, in particular, high-mass star formation are key astrophysical processes that are far from being fully understood. Unfortunately, progress in these fields is slow because observations are hard to interpret as they cannot be directly compared to numerical simulations. Synthetic observations are therefore necessary to better constrain the models. Aims. With the Rosetta Stone project, we aim to develop an end-to-end pipeline to compare star formation simulations with observations as accurately as possible in order to study the evolution from clumps scales to stars. Methods. Using the adaptive mesh-refinement code RAMSES, we computed a first grid of model of star-forming clumps to develop our pipeline and explore the impact of the clump initial conditions on their evolution. The main purpose of this set of simulations is to be converted into synthetic observations to enable a direct comparison with real star-forming clumps observed with Herschel and ALMA. Results. The Rosetta Stone simulations presented here provide a catalog available for full post-processing and subsequent comparison with observations (RS1). Among all the parameters explored here, the strength of the magnetic field has the strongest influence on the clump evolution (fragmentation, star formation, global collapse) at both large and small scales. Numerical parameters such as the resolution per Jeans length or the threshold for accretion onto sink particles affects the formation of low-mass sinks. Finally, the widely used L/M ratio is found to be a good indicator of the clump evolutionary state regardless of its initial condition, but this could change when more feedback processes (jets, HII regions) are included. Conclusions. We now have a new suite of simulations of star-forming clumps that is available for full post-processing and subsequent comparison with the observations,

Context. The evolution of massive star-forming clumps that are progenitors of high-mass young stellar objects are often classified based on a variety of observational indicators ranging from near-infrared to radio wavelengths. Among them, the ratio of the bolometric luminosity to the mass of their envelope, L/M, has been observationally diagnosed as a good indicator for the evolutionary classification of parsec-scale star-forming clumps in the Galaxy. Aims. We developed the Rosetta Stone project - an end-to-end framework designed to enable an accurate comparison between simulations and observations for investigating the formation and evolution of massive clumps. In this study, we calibrate the L/M indicator in relation to the star formation efficiency (SFE) and the clump age, as derived from our suite of simulations. Methods. We performed multi-wavelength radiative transfer post-processing of radiative magnetohydrodynamics (RMHD) simulations of the collapse of star-forming clumps fragmenting into protostars. We generated synthetic observations to obtain far-infrared emission from 70 to 500 mu m, as was done in the Hi-GAL survey, and at 24 mu m in the MIPSGAL survey, which were then used to build the spectral energy distributions (SEDs) and estimate the L/M parameter. An additional 1.3 mm wavelength in ALMA Band 6 was also produced for the comparison with observational data. We applied observational techniques - commonly employed by observers - to the synthetic data in order to derive the corresponding physical parameters. Results. We find a correlation between L/M and the SFE, with a power-law form L/M proportional to SFE-0.021.20+0.02. This correlation is independent of the mass of the clumps and the choice of initial conditions of the simulations in which they formed. The relation between L/M and the ages of the clumps is instead mass-dependent, and can also be strongly influenced by the intensity of the magnetic fields. Conclusions. Our results suggest that L/M is a reliable parameter for characterizing the overall evolutionary stage of a given starforming region. Its value can be directly compared with the star formation efficiency (SFE) parameter derived from simulations. However, to accurately infer the age of the observed clumps, it is essential to constrain their mass.

We present a comparative analysis of interstellar hydrogen (HI) and potassium (KI) absorption from the radio and optical surveys, GASKAP and GALAH, to study the physical and kinematic properties of the cold interstellar medium (ISM) in the Milky Way foreground towards the Magellanic Clouds. By comparing GASKAP HI absorption with interstellar KI absorption detected in GALAH spectra of nearby stars (within 12 arcmin angular distance or a spatial separation of 0.75 pc), we reveal a strong kinematic correlation between these two tracers of the cold neutral ISM. The velocity offsets between matched HI and KI absorption components are small, with a mean (median) offset of -1.3 (-1.2) km s-1 and a standard deviation of 2.3 km s-1. The high degree of kinematic consistency suggests a close spatial association between Ki and cold HI gas. Correlation analyses reveal a moderate positive relationship between HI and KI line-of-sight properties, such as KI column density with HI column density or HI brightness temperature. We observe a 63

This study explores the dynamical impact of cosmic rays (CRs) in Milky Way-like galaxies using the Rhea simulation suite. Cosmic rays, with their substantial energy density, influence the interstellar medium (ISM) by supporting galactic winds, modulating star formation, and shaping ISM energetics. The simulations incorporate a multiphase ISM, self-consistent CR transport in the advection-diffusion approximation, and interactions with magnetic fields to study their effects on galaxy evolution. Key findings reveal that CRs reduce star formation rates (SFRs) and drive weak, but sustained outflows with mass-loading factors of similar to 0.2, transporting a substantial fraction (20%-60%) of the injected CR energy. These CR-driven outflows are launched not just from the galactic center, but across the entire disk, illustrating their pervasive dynamical influence. Galactic disks supported by CRs exhibit broader vertical structures compared to magnetic-field-dominated setups, although the scale heights are similar. CR feedback enhances magnetic flux transport to the circumgalactic medium (CGM), leading to a magnetically enriched CGM with field strengths of similar to 0.5 mu G, while reducing gas temperatures to less than or similar to 105 K. The CR energy is relatively smoothly distributed in the disk, with gradient lengths exceeding the typical size of molecular clouds, indicating that the CR behavior is not adiabatic.

Clustered stellar feedback creates expanding voids in the magnetized interstellar medium known as superbubbles. Although theory suggests that superbubble expansion is influenced by interstellar magnetic fields, direct observational data on 3D superbubble magnetic field geometry is limited. The Sun's location inside the Local Bubble provides a unique opportunity to infer a superbubble's 3D magnetic field orientation, under the assumptions that: I) the Local Bubble's surface is the primary contributor to plane-of-the-sky polarization observations across much of the sky, and II) the Local Bubble's magnetic field is tangent to its dust-traced shell. In this work, we validate these assumptions and construct a model of the Local Bubble's 3D B-field orientation from Planck 353 GHz polarization observations and a 3D-dust-derived model of the Local Bubble's shell. We test Assumption I by examining correlations between the Local Bubble's 3D geometry, dust polarization, and starlight polarization. We find that the Local Bubble likely dominates the polarized signal in the majority of lines of sight. We jointly test Assumptions I and II by applying our reconstruction method to a simulated superbubble, where we successfully reconstruct the 3D magnetic field orientation over the bulk of its surface. Finally, we use our 3D B-field model to infer the initial magnetic field orientation in the solar neighborhood prior to the Local Bubble's formation, and derive an orientation parallel to the present-day Local Arm of the galaxy. These findings provide new insights into the co-evolution of superbubbles and the magnetized interstellar medium.

Three methods for computing the total star formation rate (SFR) of the Milky Way agree well with a reference value of 1.65 +/- 0.19 M circle dot yr-1. They are then used to determine the radial dependence of the SFR and face-on map for the Milky Way. First, the method based on a model of star formation in Hi-GAL-defined dense clumps, adjusted for an increase in the gas-to-dust ratio with Galactocentric radius, predicts 1.65 +/- 0.61 M circle dot yr-1. Second, the method using the 70 mu m emission, commonly used in other galaxies, with a technique to assign distances to the extended emission, predicts 1.42-0.44+0.63 M circle dot yr-1. Finally, a method based on theoretical predictions of star formation efficiency as a function of virial parameter, with masses corrected for metallicity dependence, applied to a catalog of molecular clouds also predicts a value in agreement at 1.47 M circle dot yr-1. The three methods predict the radial variation of the SFR, with remarkably good agreement from the Central Molecular Zone out to about 20 kpc. More differences were seen in face-on maps with a resolution of 0.5 kpc made with the three approaches and in comparisons to the local (within 3 kpc) SFR, indicating limitations of the methods when applied to smaller scales. The 70 mu m SFR follows very closely the surface density of molecular gas, corrected for a metallicity-dependent CO conversion factor. A molecular gas depletion time of 1 Gyr is consistent with the data, as is a molecular Kennicutt-Schmidt relation with a power-law slope of 1.10 +/- 0.06.