Linking nearby stellar streams to more distant halo overdensities

TL;DR

This study links local stellar halo substructures to distant overdensities by orbital analysis, revealing Gaia-Enceladus as the main contributor and predicting locations of additional debris in the Milky Way.

Contribution

It demonstrates the connection between nearby halo kinematic groups and distant stellar clouds through orbital integrations, identifying Gaia-Enceladus as the primary source.

Findings

Local halo substructures align with stellar clouds in orbital predictions.

Gaia-Enceladus dominates the contribution to the overdensities.

Orbital models predict no sky asymmetries and suggest locations for undiscovered debris.

Abstract

It has been recently shown that the halo near the Sun contains several kinematic substructures associated to past accretion events. For the more distant halo, there is evidence of large-scale density variations -- in the form of stellar clouds or overdensities. We study the link between the local halo kinematic groups and three of these stellar clouds: the Hercules-Aquila cloud, the Virgo Overdensity, and the Eridanus-Phoenix overdensity. We perform orbital integrations in a standard Milky Way potential of a local halo sample extracted from Gaia eDR3, with the goal of predicting the location of the merger debris elsewhere in the Galaxy. We specifically focus on the regions occupied by the three stellar clouds and compare their kinematic and distance distributions with those predicted from the orbits of the nearby debris. We find that the local halo substructures have families of orbits that tend to pile up in the regions where the stellar clouds have been found. The distances and velocities of the cloud's member stars are in good agreement with those predicted from the orbit integrations, particularly for Gaia-Enceladus stars. This is the dominant contributor of all three overdensities, with a minor part stemming from the Helmi streams and to an even smaller extent from Sequoia. The orbital integrations predict no asymmetries in the sky distribution of halo stars, and they pinpoint where additional debris associated with the local halo substructures may be located.