Effect of Gravity-driven Longitudinal Flows in Filaments on Angular Momentum Transport to Embedded Cores

Abstract Different models of filament formation predict distinct patterns of angular momentum redistribution toward embedded cores, set by the underlying structure of the velocity field, which can set the initial conditions for a preferential orientation between protostellar outflows and filaments. However, the absence of a dominant alignment in observations keeps this connection open to debate. We investigate whether gravity-driven longitudinal flows along filaments can redistribute angular momentum (AM) toward collapse centers. To this end, we analyze the distributions of 3D- and 2D-projected angles between sink angular momentum vectors and host filament orientations in a smoothed-particle hydrodynamics (SPH) simulation of giant molecular cloud and filament formation. We also characterize the filament velocity field by measuring the angles between SPH particle velocity vectors and filament axes, and the degree of convergent flow toward filament density peaks. No preferred alignment between the sinks’ AM and the filament direction is found at early evolutionary stages, neither in 3D nor in 2D. Later, however, a predominantly perpendicular configuration emerges in 3D. Tracking individual sinks indicates that this alignment is not primordial but develops as gravity strengthens. In individual filaments, the onset of perpendicular alignment coincides with the development of convergent longitudinal flows. Finally, we estimate the minimum excess fraction of intrinsically perpendicular 3D orientations needed for a projected sample to retain a detectable perpendicular alignment in 2D as a function of sample size, and the minimum sample size for the trend to be detectable in projection, which is at least ∼35 measurements, making conclusions from limited 2D samples potentially misleading.