IN-SYNC II: Virial Stars from Sub-Virial Cores -- The Velocity Dispersion of Embedded Pre-Main-Sequence Stars in NGC 1333

TL;DR

This study measures the velocity dispersion of young stars in NGC 1333, finding it aligns with virial expectations but exceeds core dispersions, offering insights into initial star formation dynamics.

Contribution

It provides the first direct measurement of young star velocity dispersion in NGC 1333, constraining initial conditions of star formation and suggesting magnetic fields or collapse influence.

Findings

Star velocity dispersion is 0.92 km/s, consistent with virial velocity.

Dense cores have a sub-virial velocity dispersion of 0.5 km/s.

Implications for magnetic fields or cluster collapse dynamics.

Abstract

The initial velocity dispersion of newborn stars is a major unconstrained aspect of star formation theory. Using near-infrared spectra obtained with the APOGEE spectrograph, we show that the velocity dispersion of young (1-2 Myr) stars in NGC 1333 is 0.92+/-0.12 km/s after correcting for measurement uncertainties and the effect of binaries. This velocity dispersion is consistent with the virial velocity of the region and the diffuse gas velocity dispersion, but significantly larger than the velocity dispersion of the dense, star-forming cores, which have a sub-virial velocity dispersion of 0.5 km/s. Since the NGC 1333 cluster is dynamically young and deeply embedded, this measurement provides a strong constraint on the initial velocity dispersion of newly-formed stars. We propose that the difference in velocity dispersion between stars and dense cores may be due to the influence of a 70 micro-Gauss magnetic field acting on the dense cores, or be the signature of a cluster with initial sub-structure undergoing global collapse.