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 velocity-field structure, 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 and influence outflow-filament alignment. To this end, we analyze the distributions of 3D and 2D-projected angles between sink angular momentum vectors and host filament orientations in an 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 fraction of perpendicular 3D angles required to reveal a perpendicular 2D alignment for a given sample size. While longitudinal flows develop over extended timescales, once established, they can rapidly reorient the angular momentum vector of the sinks, enabling perpendicular alignments to arise within typical outflow lifetimes.

Figures (14)

• Figure 1: A) Prediction of perpendicular OFA in the model presented by Anathprindika.Withworth2008. The misalignment of gas inflows toward the hub generates a net torque that induces rotation, such that the resulting angular momentum vector ($\vec{J}$) of the hub—and subsequently the outflows direction—is oriented perpendicular to the major axis of the filament. B) Prediction of pparallel OFA in the model presented by Banerjee.Pudritz.Anderson2006. The core inherits the filament’s rotation about its major axis, such that $\vec{J}$ is parallel to the filament axis.
• Figure 2: Projected density field in run HDG3 (first row) at times $t=5.4, 8, 11,14$, and $17.5$ Myr. The second row shows the spines of the filaments in cyan detected by the DisPerSE on top of the density field. White dots represent the sinks particles.
• Figure 3: A) Representative scheme for the calculation between the angular momentum vector of a sink (large white circles) represented in purple, ${\bm j}_{\rm sink}$, and the filament direction shown in pink, calculated from the point on the spine closest to the sink. Sinks are assigned to a filament if they are at a distance $\leq 0.5$ pc from the spine. B) Schematic drawing showing the calculation of the angle between the bulk-subtracted velocity vector of the particles around the filament, ${\bm V}_i$, and the filament direction, f. A test SPH particle, $P_i$, is shown as an example in yellow. The filament direction is also calculated from the point on the spine closest to the particle. The process is repeated for all particles around the spine for $R=0.5$ pc. C) Projection of the SPH particle velocity vectors along the major axis of the filament, determined from a 3D fit of the spine points. The zero position is defined as the projected spine point whose associated particles have the highest mean density.
• Figure 4: From top to bottom, the first and third plots show the evolution of the histograms of the 3D angle and its cosine, respectively, between the angular momentum vector of the sinks and the direction of the associated filament, $\theta_{{\rm s,3D}}$, for the full numerical sample of sinks. The second and fourth plots are the same, but the sinks are tracked only during the first $0.5$ Myr after their formation. A tendency towards perpendicularity can be seen at later times for the sinks without the time restriction, both in the angle and its cosine, while in the reduced sample, the overall trend seems rather random.
• Figure 5: Trajectories followed by $10$ sinks (differentiated by color) from their time of formation. The trajectories are plotted over the histogram evolution of $\theta_{{\rm s,3D}}$ (top) and $cos(\theta_{{\rm s,3D}})$ (bottom) for the non-restricted sample case shown in Figure \ref{['fig:OFA evolution with gravity']}. Solid lines represent time periods with continuous data (see text), while dotted lines represent periods in which sinks are not assigned to any filament for at least $0.3$ Myr. At early times, a drastic oscillation is observed in $\theta_{{\rm s,3D}}$ measurement, while at later times the oscillation is around angles closer to $90\degree$.