ORION-4D: towards a unified theory of star formation

Sun-like stars are formed inside molecular clouds after the gravitational collapse of condensations of gas known as dense cores. The recent far-infrared Herschel Space Observatory data indicate that dense cores are embedded inside long structures of gas called filaments. However, the physical mechanisms responsible for this hierarchical cloud structure remains a major open question in the field of star formation. In a groundbreaking work, I first demonstrated that some of the apparently monolithic filaments seen by these Herschel observations actually consist of collections of small scale structures referred to as fibers. Identified by the continuity of their internal velocity fields, an information only accessible from the study of millimeter line observations, these fibers are characterized by mass distributions close to the hydrostatic equilibrium, sizes of $\sim$~0.5~pc, and sonic-like motions. Organized in complex networks, these fibers precede and control the formation of dense cores. Moreover, they are recognized as the fundamental building blocks of low-mass clouds and filaments. I propose to extend this novel line of work to the domain of massive clouds, the structures responsible for the formation of most of the stars in our Galaxy. I will accomplish this with observations of the prototypical Orion A cloud using my new research program, namely ORION- 4D, the largest millimeter line survey of this cloud carried out to date. Combining single-dish and ALMA interferometric observations of 30 molecular species, I will systematically characterize the physical properties and the internal structure (density, temperature, velocity structure, etc) of approximately 150 filaments, 200 cores, and 12 cluster inside this star-forming region. The statistical significance of these results will provide the most extensive sample for these type of structures measured so far in massive molecular clouds. For that, I will integrate state-of-the-art radiative transfer codes into the newest analysis tools for the gas kinematics. Local and global comparisons will serve as unique benchmarks to directly test theoretical models of cloud formation and evolution. These results could potentially lead to a universal description of the star formation process in our Galaxy, unifying our current theories for both low- and high-mass stars.