Disconnecting the Dots: Re-Examining the Nature of Stellar "Strings" in the Milky Way

Abstract

Recent analyses of Gaia data have resulted in the identification of new stellar structures, including a new class of extended stellar filaments called stellar "strings", first proposed by Kounkel and Covey 2019. We explore the spatial, kinematic, and chemical composition of strings to demonstrate that these newfound structures are largely inconsistent with being physical objects whose members share a common origin. Examining the 3D spatial distribution of string members, we find that the spatial dispersion around the claimed string spine does not improve in the latest Gaia DR3 data release -- despite tangible gains in the signal-to-noise of the parallax measurements -- counter to expectations of a bona fide structure. Using the radial velocity dispersion of the strings (averaging ${\sigma }_{{\mathrm{V}}_{\mathrm{r}}}=16\mathrm{km}{\mathrm{s}}^{-1}$) to estimate their virial masses, we find that all strings are gravitationally unbound. Given the finding that the strings are dispersing, the reported stellar ages of the strings are typically $120\times$ larger than their measured dispersal times. Finally, we validate prior work that stellar strings are more chemically homogeneous than their local field stars, but show it is possible to obtain the same signatures of chemical homogeneity by drawing random samples of stars from spatially, temporally, and kinematically unrelated open clusters. Our results show that while some strings may be composed of real sub-structures, there is no consistent evidence for larger string-like connections over the sample. These results underline the need for caution in over-interpreting the significance of these strings and their role in understanding the star formation history of the Milky Way.

Accepted for publication in The Astrophysical Journal

References in corpus (26)

• The Gaia mission
• New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey
• The GALAH+ Survey: Third Data Release
• APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South
• Hunting for open clusters in \textit{Gaia} DR2: $582$ new OCs in the Galactic disc
• Large-scale filaments associated with Milky Way spiral arms
• The Bones of the Milky Way
• 3D kinematics and age distribution of the Open Cluster population
• Extended stellar systems in the solar neighborhood -- V. Discovery of coronae of nearby star clusters
• The GALAH survey: tracing the Galactic disk with Open Clusters
• Extended stellar systems in the solar neighborhood - I. The tidal tails of the Hyades
• Untangling the Galaxy. II. Structure within 3 kpc
• Extended stellar systems in the solar neighborhood - II. Discovery of a nearby 120° stellar stream in Gaia DR2
• Early turbulent mixing as the origin of chemical homogeneity in open star clusters
• Inside Out and Upside-Down: The Roles of Gas Cooling and Dynamical Heating in Shaping the Stellar Age-Velocity Relation
• Palomar 5 and its Tidal Tails: A Search for New Members in the Tidal Stream
• Uncovering a 260 pc wide, 35 Myr old filamentary relic of star formation
• Extended stellar systems in the solar neighborhood. IV. Meingast 1: the most massive stellar stream in the solar neighborhood
• Velocity Dispersion of the GD-1 Stellar Stream
• Discovery of a young stellar "snake" with two dissolving cores in the solar neighborhood
• The Chemical Nature of the Young 120-Myr-old Nearby Pisces-Eridanus Stellar Stream Flowing through the Galactic Disk
• A Young, Low-Density Stellar Stream in the Milky Way Disk: Theia 456
• Synthetic Large-Scale Galactic Filaments -- on their Formation, Physical Properties, and Resemblance to Observations
• Pearls on a String: Numerous Stellar Clusters Strung along the Same Orbit
• The Stellar "Snake" I: Whole Structure and Properties
• A GALAH View of the Chemical Homogeneity and Ages of Stellar Strings Identified in Gaia

Cited by in corpus (8)

• Improving the open cluster census. II. An all-sky cluster catalogue with Gaia DR3
• Improving the open cluster census. III. Using cluster masses, radii, and dynamics to create a cleaned open cluster catalogue
• Tidal tails of open clusters
• Using the Gaia excess uncertainty as a proxy for stellar variability and age
• Exploring Galactic open clusters with Gaia I. An examination in the first kiloparsec
• Lost Sisters Found: TESS and Gaia Reveal a Dissolving Pleiades Complex
• Toward the fabric of the Milky Way I. The density of disk streams from a local $250^3$ pc${}^3$ volume
• Tidal tails in open clusters: Morphology, binary fraction, dynamics, and rotation