Was the Progenitor of the Sagittarius Stream a Disc Galaxy?

TL;DR

This study uses N-body simulations to investigate if the Sagittarius dwarf galaxy was originally a rotating disc galaxy, revealing that its progenitor's rotation influences stream bifurcations and could be detected in future surveys.

Contribution

It demonstrates that a rotating disc progenitor can explain observed stream features and impacts dark matter halo constraints, a novel perspective in Sgr stream modeling.

Findings

Bifurcations in the Sgr stream can arise from a misaligned disc progenitor.

Progenitor rotation affects the stream's projected position, influencing halo shape constraints.

Remnant core of the progenitor should still rotate at ~20 km/s, detectable in future surveys.

Abstract

We use N-body simulations to explore the possibility that the Sagittarius (Sgr) dwarf galaxy was originally a late-type, rotating disc galaxy, rather than a non-rotating, pressure-supported dwarf spheroidal galaxy, as previously thought. We find that bifurcations in the leading tail of the Sgr stream, similar to those detected by the SDSS survey, naturally arise in models where the Sgr disc is misaligned with respect to the orbital plane. Moreover, we show that the internal rotation of the progenitor may strongly alter the location of the leading tail projected on the sky, and thus affect the constraints on the shape of the Milky Way dark matter halo that may be derived from modelling the Sgr stream. Our models provide a clear, easily-tested prediction: although tidal mass stripping removes a large fraction of the original angular momentum in the progenitor dwarf galaxy, the remnant core should still rotate with a velocity amplitude ~20 km/s that could be readily detected in future, wide-field kinematic surveys of the Sgr dwarf.