Constraining the orbital history of the Magellanic Clouds: A new bound scenario suggested by the tidal origin of the Magellanic Stream

TL;DR

This paper proposes a new tidal model for the Magellanic Clouds that explains the formation of the Magellanic Stream and Leading Arm within a bound orbital scenario consistent with recent HST proper motion measurements.

Contribution

It introduces a tidal model where the Magellanic Stream and Leading Arm form from recent LMC-SMC interactions, challenging previous unbound orbit assumptions.

Findings

The model reproduces the bifurcated Magellanic Stream.

The LMC and SMC have been bound to each other only recently.

The model supports a massive Milky Way halo with V_cir=250 km/s.

Abstract

Bound orbits have traditionally been assigned to the Large and Small Magellanic Clouds (LMC and SMC, respectively) in order to provide a formation scenario for the Magellanic Stream (MS) and its Leading Arm (LA), two prominent neutral hydrogen (HI) features connected to the LMC and SMC. However, Hubble Space Telescope (HST) measurements of the proper motions of the LMC and SMC have challenged the plausibility of bound orbits, causing the origin of the MS to re-emerge as a contested issue. We present a new tidal model in which structures resembling the bifurcated MS and elongated LA are able to form in a bound orbit consistent with the HST proper motions. The LMC and SMC have remained bound to each other only recently in our model despite being separately bound to the Milky Way for more than 5 Gyr. We find that the MS and LA are able to form as a consequence of LMC-dominated tidal stripping during the recent dynamical coupling of the LMC and SMC. Our orbital model depends on our assumption that the Milky Way has a constant circular velocity of V_cir=250 km/s up to 160 kpc, which implies a massive isothermal halo that is not completely rejected by observations.