Vol. 703
5. Galactic structure, stellar clusters and populations

The large-scale kinematics of young stars in the Milky Way disc: First results from SDSS-V

Zari et al. present maps of the 3D motions of about 50 000 hot, young stars, using SDSS-V spectroscopy together with Gaia astrometry. The map reaches roughly to about 5 kpc from the Sun. The key result is the detection of strong radial motions, coherent flows of stars with amplitudes up to +/-30 km/s that alternate between inward and outward over kiloparsec scales. These flows are much stronger than those measured for older red-giant samples. Inside the solar circle the average motion is mostly inward, while outside it tends to be outward, although the pattern varies by location.

The youngest stars, with ages ~< 30 Myr, sit within stellar density enhancements that trace known star-forming regions, yet the global streaming pattern only weakly follows spiral-arm overdensities. This points to multiple drivers rather than a single tidy link to the arms. A simple picture is that both the Galactic bar and spiral structure shape these flows. The present analysis uses roughly one third of the planned SDSS-V sample, so future maps should tighten constraints on these mechanisms.