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Gas cooling processes in the interstellar medium (ISM) are key to understanding how star-formation processes occur in galaxies. Far-infrared (FIR) fine-structure emission lines can be used as a tool to understand the gas conditions and trace the different phases of the ISM. We model the most important far-infrared (FIR) emission lines throughout cosmic time back to $z=6$ with cosmological hydrodynamical simulations. We study how different physical parameters, such as the interstellar radiation field (ISRF) and metallicity, impact the ISM phases traced by FIR line luminosities and connect those with the star-formation rate (SFR). We implement a physically motivated multi-phase model of the ISM by post-processing EAGLE cosmological simulation with Cloudy look-up tables. In this model, we assume four phases of the ISM: dense molecular gas, neutral atomic gas, diffuse ionised gas (DIG) and HII regions. Our model shows good agreement with the observed luminosity-SFR relation up to $z=6$ in the FIR emission lines analysed and we also provide linear fits. Our predictions also agree with observations in terms of diagnostic diagrams involving various line ratios. We find that [C II] is the best SFR tracer of the FIR lines even though it traces multiple ISM phases, while [O III] and [N II] can be used to understand the DIG-HII balance in the ionised phase. In addition, line ratios like [C II]/[O III] and [N II/[O I] are useful to trace parameters such as ISRF, metallicity and specific star-formation rate. These results help to interpret observations of FIR line emission from the local Universe to high-$z$ galaxies., Comment: 22 pages, 18 figures, 3 tables (plus appendix). Submitted to A&A

Interest in stellar feedback has recently increased because new studies suggest that radiative and mechanical feedback from young massive stars regulate the physical and chemical composition of the interstellar medium (ISM) significantly. Recent SOFIA [CII] 158 micron observations of the Orion Veil revealed that the expanding bubble is powered by stellar winds and influenced by previously active molecular outflows of ionizing massive stars. We aim to investigate the mechanical feedback on the whole Veil shell by searching for jets/outflows interacting with the Veil shell and determining the origin/driving mechanisms of these collisions. In the light of these findings, as well as the momenta of the dents and their dynamical timescales, we propose that the dents are created by the interaction of collimated jets/outflows from protostars with luminosities ranging from 10$^3$ to 10$^4$ $L_\odot$ indicating B-type stars in the Orion star-forming cloud with the surrounding Veil shell. However, it is challenging to pinpoint the driving stars as they may have moved from the original ejection points of the jets/outflows. We conclude that the dynamics of the expanding Veil shell is influenced not just by the O-type stars in the Trapezium cluster, but also by less massive stars, especially B-type, in the Orion Nebula. Mechanical feedback from protostars with a range of masses appears to play an important role in determining the morphology of [HII] regions and injecting turbulence into the medium., Comment: 18 pages, 18 figures, Accepted by A&A on March 22, 2022

The role of feedback in the self-regulation of star formation is a fundamental question in astrophysics. The Orion Nebula is the nearest site of ongoing and recent massive star formation. It is a unique laboratory for the study of stellar feedback. Recent SOFIA [CII] 158 $\mu$m observations revealed an expanding bubble, the Veil shell, being powered by stellar winds and ionization feedback. We have identified a protrusion-like substructure in the Northwest portion of the Orion Veil Shell that may indicate additional feedback mechanisms that are highly directional. Our goal is to investigate the origin of the protrusion by quantifying its possible driving mechanisms. We use the [CII] 158 $\mu$m map of the Orion Nebula obtained with the upGREAT instrument onboard SOFIA. The spectral and spatial resolution of the observations are 0.3 km/s and 16 arcsec, respectively. We consider three possible origins for this protrusion: Fossil outflow cavities created by jets/outflows during the protostellar accretion phase, pre-existing clumpiness in the OMC-1 core, and the stellar wind during the main sequence phase. Based on the energetics and the morphology, we conclude that the northwestern part of the pre-existing cloud was locally perturbed by outflows ejected from massive protostars in the Trapezium cluster. This suggests that the protrusion of the Veil is the result of mechanical rather than radiative feedback. Furthermore, we argue that the location of the protrusion is a suitable place to break the Orion Veil owing to the photo-ablation from the walls of the protrusion. We conclude that the outflows of massive protostars can influence the morphology of the future \hii\,region and even cause breakages in the ionization front. Specifically, the interaction of stellar winds of main-sequence stars with the molecular core pre-processed by the protostellar jet is important., Comment: Accepted by A&A on Feb 9, 2022 (20 pages, 19 figures)