Emergence of high-mass stars in complex fiber networks (EMERGE)

Context . Over the past decade, Herschel far-infrared (FIR) observations have demonstrated the complex organisation characterising the interstellar medium as networks of parsec-scale filaments. At the same time, fiber networks have been found to aptly describe the gas structures in star-forming regions at sub-parsec scales. Aims . We aim to investigate the dense gas organisation prior to the formation of stars in a selected sample of regions within Orion. Methods . We surveyed seven prototypical star-forming regions in Orion as part of the EMERGE Early ALMA Survey. Our sample includes low- (OMC-4 South, NGC 2023), intermediate- (OMC-2, OMC-3, LDN 1641N), and high-mass (OMC-1, Flame Nebula) star-forming regions all surveyed at a high spatial resolution of 4.5″(or ∼2000 au) in N 2 H + (1-0). We used a dedicated series of ALMA+IRAM-30 m observations of this homogeneous sample to systematically investigate the spatial distribution, density, and thermal structure of the star-forming gas, along with its column density variations and its internal motions in a wide range of environments. Results . From the analysis of the gas kinematics, we identified and characterised a total of 152 velocity-coherent fibers. The statistical significance of our sample, the largest of its kind so far, highlights these small-scale filamentary sub-structures as the preferred organisational unit for the dense gas in low-, intermediate-, and high-mass star-forming regions alike. Despite the varied complexity of these sub-parsec networks (in terms of the surface density of their constituent fibers), the masses and lengths of these objects show similar distributions and consistent median values, as well as (trans-)sonic motions, for all of our targets. The comparison between the fiber line masses and virial line masses suggests that the majority of these objects are sub-virial. Those fibers closer to the virial condition, however, are also associated with a greater number of protostars. Finally, the surface density of fibers is linearly correlated with the total dense gas mass throughout by roughly one order of magnitude in terms of both of these parameters. Conclusions . While most fibers show comparable mass, length, and internal motions in our survey, massive fibers that are close to the virial condition are shown to be intimately connected to star formation. The majority of the protostars in our target regions are, in fact, associated with these objects. The additional correlation between the surface density of fibers and the dense gas mass in our survey demonstrates how the physical properties of fibers can explain the current degree of star formation in their host region. Our findings suggest a common mechanism for star formation from low- to high-mass star-forming regions, mediated through the formation and evolution of fiber networks.