Icarus: a Flat and Fast Prograde Stellar Stream in the Milky Way disk

Abstract

We explore the local volume of the Milky Way via chemical and kinematical measurements from high quality astrometric and spectroscopic data recently released by the Gaia, APOGEE and GALAH programs. We chemically select $1137$ stars up to $2.5$~kpc of the Sun and $[Fe/H]\le -1.0$~dex, and find evidence of statistically significant substructures. Clustering analysis in velocity space classifies $163$ objects into eight kinematical groups, whose origin is further investigated with high resolution N-body numerical simulations of single merging events. The two retrograde groups appear associated with Gaia-Sausage-Enceladus, while the slightly prograde group could be connected to GSE or possibly Wukong. We find evidence of a new 44-member-strong prograde stream we name Icarus; to our knowledge, Icarus is the fast-rotating stream closest to the Galactic disk to date ($⟨Z_{\max }⟩\lesssim 0.5$~kpc, $⟨V+V_{\mathrm{LSR}}⟩\simeq 231\mathrm{km}{\mathrm{s}}^{-1}$). Its peculiar chemical ($⟨[Fe/H]⟩\simeq -1.45$, $⟨[Mg/Fe]⟩\simeq -0.02$) and dynamical (mean eccentricity $\simeq 0.11$) properties are consistent with the accretion of debris from a dwarf galaxy progenitor with a stellar mass of $\sim 10^9 M_\sun$ on an initial prograde low-inclination orbit, $\sim 10^{\circ }$. The remaining prograde groups are either streams previously released by the same progenitor of Icarus (or Nyx), or remnants from different satellites accreted on initial orbits at higher inclination.

9 pages, 4 figures, 1 Table. Accepted for publication into The Astrophysical Journal Letters

References in corpus (7)

• galpy: A Python Library for Galactic Dynamics
• The mass distribution and gravitational potential of the Milky Way
• The GALAH Survey: Scientific Motivation
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• The GALAH survey: The data reduction pipeline
• The Gaia-ESO Survey: a quiescent Milky Way with no significant dark/stellar accreted disc

Cited by in corpus (2)

• A New Cold Stream near the Southern Galactic Pole
• A Dwarf Galaxy Debris Stream Associated with Palomar 1 and the Anticenter Stream