Toward the fabric of the Milky Way

I. The density of disk streams from a local 250³ pc³ volume

¹ University of Vienna, Department of Astrophysics, Türkenschanzstraße 17, 1180 Vienna, Austria
² University of Vienna, Research Network Data Science at Uni Vienna, Kolingasse 14-16, 1090 Vienna, Austria
³ University of Vienna, Faculty of Computer Science, Währinger Straße 29/S6, 1090 Vienna, Austria
⁴ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany

^★ Corresponding author; sebastian.ratzenboeck@univie.ac.at

Received: 12 August 2024
Accepted: 6 January 2025

Abstract

We studied 12 disk streams found in a 250³ pc³ volume in the solar neighborhood, which we define as coeval and comoving stellar structures with aspect ratios greater than 3:1. Using Gaia Data Release 3 data and the advanced clustering algorithms SigMA and Uncover, we identified and characterized these streams beyond the search volume, doubling, on average, their known populations. We estimate the number density of disk streams to be ≈820 objects/kpc³ (for |Z| < 100 pc), or surface densities of ≈160 objects/kpc². These estimates surpass N-body estimates by one to two orders of magnitude and challenge the prevailing understanding of their destruction mechanisms. Our analysis reveals that these 12 disk streams are dynamically cold with 3D velocity dispersions between 2 and 5 km s⁻¹, exhibit narrow sequences in the Hertzsprung-Russell diagram, and are highly elongated with average aspect ratios of 7:1, extending up to several hundred parsecs. We find evidence suggesting that one of the disk streams, currently embedded in the Scorpius-Centaurus association, is experiencing disruption, likely due to the primordial gas mass of the association.