On the genealogy of the Orphan Stream

TL;DR

This paper uses N-body simulations to trace the origin and orbit of the faint Orphan Stream, suggesting it originated from a dwarf galaxy similar to Carina or Draco, and highlighting the difficulty of detecting such low surface brightness streams.

Contribution

It presents a plausible orbit and progenitor for the Orphan Stream using N-body simulations, linking it to known dwarf galaxies and emphasizing the challenge of detecting faint streams.

Findings

The Orphan Stream can be modeled as a single wrap of a double-component satellite.

Progenitors similar to Carina, Draco, Leo II, or Sculptor are likely origins.

Low surface brightness streams are common but hard to detect with current methods.

Abstract

We use N-body simulations to explore the origin and a plausible orbit for the Orphan Stream, one of the faintest substructures discovered so far in the outer halo of our Galaxy. We are able to reproduce its position, velocity and distance measurements by appealing to a single wrap of a double-component satellite galaxy. We find that the progenitor of the Orphan Stream could have been an object similar to today's Milky Way dwarfs, such as Carina, Draco, Leo II or Sculptor; and unlikely to be connected to Complex A or Ursa Major II. Our models suggest that such progenitors, if accreted on orbits with apocenters smaller than ~35 kpc, are likely to give rise to very low surface brightness streams, which may be hiding in the outer halo and remain largely undetected with current techniques. The systematic discovery of these ghostly substructures may well require wide field spectroscopic surveys of the Milky Way's outer stellar halo.