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Nearby Photo-Dissociation Regions (PDRs), where the gas and dust are heated by the far UV-irradiation emitted from stars, are ideal templates to study the main stellar feedback processes. With this study we aim to probe the detailed structures at the interfaces between ionized, atomic, and molecular gas in the Orion Bar. This nearby prototypical strongly irradiated PDR will be among the first targets of the James Webb Space Telescope (JWST) within the framework of the PDRs4All Early Release Science program. We employed the sub-arcsec resolution accessible with Keck-II NIRC2 and its adaptive optics system to obtain the most detailed and complete images, ever performed, of the vibrationally excited line H$_2$ 1-0 S(1) at 2.12~$\mu$m, tracing the dissociation front, and the [FeII] and Br$\gamma$ lines, at 1.64 and 2.16~$\mu$m respectively, tracing the ionization front. We obtained narrow-band filter images in these key gas line diagnostic over $\sim 40''$ at spatial scales of $\sim$0.1$''$ ($\sim$0.0002~pc or $\sim$40~AU at 414~pc). The Keck/NIRC2 observations spatially resolve a plethora of irradiated sub-structures such as ridges, filaments, globules and proplyds. A remarkable spatial coincidence between the H$_2$ 1-0 S(1) vibrational and HCO$^+$ J=4-3 rotational emission previously obtained with ALMA is observed. This likely indicates the intimate link between these two molecular species and highlights that in high pressure PDR the H/H$_2$ and C$^+$/C/CO transitions zones come closer as compared to a typical layered structure of a constant density PDR. This is in agreement with several previous studies that claimed that the Orion Bar edge is composed of very small, dense, highly irradiated PDRs at high thermal pressure immersed in a more diffuse environment.

[Context] Massive colliding-wind binaries (CWBs) can be non-thermal sources. The emission produced in their wind-collision region (WCR) encodes information of both the shock properties and the relativistic electrons accelerated in them. The recently discovered system Apep, a unique massive system hosting two Wolf-Rayet stars, is the most powerful synchrotron radio emitter among the known CWBs. It is an exciting candidate in which to investigate the non-thermal processes associated with stellar wind shocks., [Aims] We intend to break the degeneracy between the relativistic particle population and the magnetic field strength in the WCR of Apep by probing its hard X-ray spectrum, where inverse-Compton (IC) emission is expected to dominate., [Methods] We observed Apep with NuSTAR for 60 ks and combined this with a reanalysis of a deep archival XMM-Newton observation to better constrain the X-ray spectrum. We used a non-thermal emission model to derive physical parameters from the results., [Results] We detect hard X-ray emission consistent with a power-law component from Apep. This is compatible with IC emission produced in the WCR for a magnetic field of ≈105–190 mG, corresponding to a magnetic-to-thermal pressure ratio in the shocks of ≈0.007–0.021, and a fraction of ∼1.5 × 10−4 of the total wind kinetic power being transferred to relativistic electrons., [Conclusions] The non-thermal emission from a CWB is detected for the first time in radio and at high energies. This allows us to derive the most robust constraints so far for the particle acceleration efficiency and magnetic field intensity in a CWB, reducing the typical uncertainty of a few orders of magnitude to just within a factor of a few. This constitutes an important step forward in our characterisation of the physical properties of CWBs.

Context. The [C II] 158 m fine-structure line is the dominant cooling line of moderate-density photodissociation regions (PDRs) illuminated by moderately bright far-ultraviolet (FUV) radiation fields. This makes this line a prime diagnostic for extended regions illuminated by massive stars. Aims. We aim to understand the origin of [C II] emission and its relation to other tracers of gas and dust in PDRs. One focus is a study of the heating efficiency of interstellar gas as traced by the [C II] line to test models of the photoelectric heating of neutral gas by polycyclic aromatic hydrocarbon (PAH) molecules and very small grains. Methods. We make use of a one-square-degree map of velocity-resolved [C II] line emission toward the Orion Nebula complex, and split this out into the individual spatial components, the expanding Veil Shell, the surface of OMC4, and the PDRs associated with the compact H II region of M43 and the reflection nebula NGC 1977. We employed Herschel far-infrared photometric images to determine dust properties. Moreover, we compared with Spitzer mid-infrared photometry to trace hot dust and large molecules, and velocity-resolved IRAM 30m CO(2-1) observations of the molecular gas. Results. The [C II] intensity is tightly correlated with PAH emission in the IRAC 8 m band and far-infrared emission from warm dust, with small variations between the four studied subregions (Veil Shell, OMC4, M43, and NGC 1977). The correlation between [C II] and CO(2-1) is very different in the four subregions and is very sensitive to the detailed geometry of the respective regions. Constant-density PDR models are able to reproduce the observed [C II], CO(2-1), and integrated far-infrared (FIR) intensities. The physical conditions in the Veil Shell of the Orion Nebula, M43, and NGC 1977 reveal a constant ratio of thermal pressure pth over incident FUV radiation field measured by G0. We observe strong variations in the photoelectric heating efficiency in the Veil Shell be

[Aims] We aim to characterise certain physical properties of high-mass star-forming sites in the NGC 6334 molecular cloud, such as the core mass function (CMF), spatial distribution of cores, and mass segregation., [Methods] We used the Atacama Large Millimeter/sub-millimeter Array (ALMA) to image the embedded clusters NGC 6334-I and NGC 6334-I(N) in the continuum emission at 87.6 GHz. We achieved a spatial resolution of 1300 au, enough to resolve different compact cores and fragments, and to study the properties of the clusters., [Results] We detected 142 compact sources distributed over the whole surveyed area. The ALMA compact sources are clustered in different regions. We used different machine-learning algorithms to identify four main clusters: NGC 6334-I, NGC 6334-I(N), NGC 6334-I(NW), and NGC 6334-E. The typical separations between cluster members range from 4000 au to 12 000 au. These separations, together with the core masses (0.1–100 M⊙), are in agreement with the fragmentation being controlled by turbulence at scales of 0.1 pc. We find that the CMFs show an apparent excess of high-mass cores compared to the stellar initial mass function. We evaluated the effects of temperature and unresolved multiplicity on the derived slope of the CMF. Based on this, we conclude that the excess of high-mass cores might be spurious and due to inaccurate temperature determinations and/or resolution limitations. We searched for evidence of mass segregation in the clusters and we find that clusters NGC 6334-I and NGC 6334-I(N) show hints of segregation with the most massive cores located in the centre of the clusters., [Conclusions] We searched for correlations between the physical properties of the four embedded clusters and their evolutionary stage (based on the presence of H II regions and infrared sources). NGC 6334-E appears as the most evolved cluster, already harbouring a well-developed H II region. NGC 6334-I is the second-most evolved cluster with an ultra-compact H II region. NGC 6334-I(N) contains the largest population of dust cores distributed in two filamentary structures and no dominant H II region. Finally, NGC 6334-I(NW) is a cluster of mainly low-mass dust cores with no clear signs of massive cores or H II regions. We find a larger separation between cluster members in the more evolved clusters favouring the role of gas expulsion and stellar ejection with evolution. The mass segregation, seen in the NGC 6334-I and NGC 6334-I(N) clusters, suggests a primordial origin for NGC 6334-I(N). In contrast, the segregation in NGC 6334-I might be due to dynamical effects. Finally, the lack of massive cores in the most evolved cluster suggests that the gas reservoir is already exhausted, while the less evolved clusters still have a large gas reservoir along with the presence of massive cores. In general, the fragmentation process of NGC 6334 at large scales (from filament to clump, i.e. at about 1 pc) is likely governed by turbulent pressure, while at smaller scales (scale of cores and sub-fragments, i.e. a few hundred au) thermal pressure starts to be more significant.