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The dwarf galaxy Triangulum (M33) presents an interesting testbed for studying stellar halo formation: it is sufficiently massive so as to have likely accreted smaller satellites, but also lies within the regime where feedback and other “in situ” formation mechanisms are expected to play a role. In this work, we analyze the line-of-sight kinematics of stars across M33 from the TREX survey, with a view to understanding the origin of its halo. We split our sample into two broad populations of varying age, comprising 2032 “old” red giant branch stars and 671 “intermediate-age” asymptotic giant branch and carbon stars. We find decisive evidence for two distinct kinematic components in both the old and intermediate-age populations: a low-dispersion (∼22 km s⁻¹) disk-like component corotating with M33's Higas and a significantly higher-dispersion component (∼50–60 km s⁻¹) that does not rotate in the same plane as the gas and is thus interpreted as M33's stellar halo. While kinematically similar, the fraction of stars associated with the halo component differs significantly between the two populations: this is consistently ∼10% for the intermediate-age population, but decreases from ∼34% to ∼10% as a function of radius for the old population. We additionally find evidence that the intermediate-age halo population is systematically offset from the systemic velocity of M33 by ∼25 km s⁻¹, with a preferred central LOS velocity of ∼ − 155 km s⁻¹. This is the first detection and characterization of an intermediate-age halo in M33, and suggests in situ formation mechanisms, as well as potentially tidal interactions, have helped shaped it.

 

We use data from the Magellanic Edges Survey (MagES) in combination with Gaia EDR3 to study the extreme southern outskirts of the Small Magellanic Cloud (SMC), focussing on a field at the eastern end of a long arm-like structure which wraps around the southern periphery of the Large Magellanic Cloud (LMC). Unlike the remainder of this structure, which is thought to be comprised of perturbed LMC disc material, the aggregate properties of the field indicate a clear connection with the SMC. We find evidence for two stellar populations in the field: one having properties consistent with the outskirts of the main SMC body, and the other significantly perturbed. The perturbed population is on average ∼0.2 dex more metal-rich, and is located ∼7 kpc in front of the dominant population with a total space velocity relative to the SMC centre of ∼230 km s−1 broadly in the direction of the LMC. We speculate on possible origins for this perturbed population, the most plausible of which is that it comprises debris from the inner SMC that has been recently tidally stripped by interactions with the LMC.

 

We explore the structural and kinematic properties of the outskirts of the Large Magellanic Cloud (LMC) using data from the Magellanic Edges Survey (MagES) and Gaia EDR3. Even at large galactocentric radii (8° < R < 11°), we find the north-eastern LMC disc is relatively unperturbed: its kinematics are consistent with a disc of inclination ∼36.5° and line-of-nodes position angle ∼145° east of north. In contrast, fields at similar radii in the southern and western disc are significantly perturbed from equilibrium, with non-zero radial and vertical velocities, and distances significantly in front of the disc plane implied by our north-eastern fields. We compare our observations to simple dynamical models of the Magellanic or Milky Way system which describe the LMC as a collection of tracer particles within a rigid potential, and the Small Magellanic Cloud (SMC) as a rigid Hernquist potential. A possible SMC crossing of the LMC disc plane ∼400 Myr ago, in combination with the LMC’s infall to the Milky Way potential, can qualitatively explain many of the perturbations in the outer disc. Additionally, we find the claw-like and arm-like structures south of the LMC have similar metallicities to the outer LMC disc ([Fe/H] ∼ −1), and are likely comprised of perturbed LMC disc material. The claw-like substructure is particularly disturbed, with out-of-plane velocities >60 km s−1 and apparent counter-rotation relative to the LMC’s disc motion. More detailed N-body models are necessary to elucidate the origin of these southern features, potentially requiring repeated interactions with the SMC prior to ∼1 Gyr ago.

 

The highly-substructured outskirts of the Magellanic Clouds provide ideal locations for studying the complex interaction history between both Clouds and the Milky Way (MW). In this paper, we investigate the origin of a >20° long arm-like feature in the northern outskirts of the Large Magellanic Cloud (LMC) using data from the Magellanic Edges Survey (MagES) and Gaia EDR3. We find that the arm has a similar geometry and metallicity to the nearby outer LMC disc, indicating that it is comprised of perturbed disc material. Whilst the azimuthal velocity and velocity dispersions along the arm are consistent with those in the outer LMC, the in-plane radial velocity and out-of-plane vertical velocity are significantly perturbed from equilibrium disc kinematics. We compare these observations to a new suite of dynamical models of the Magellanic/MW system, which describe the LMC as a collection of tracer particles within a rigid potential, and the SMC as a rigid Hernquist potential. Our models indicate the tidal force of the MW during the LMC’s infall is likely responsible for the observed increasing out-of-plane velocity along the arm. Our models also suggest close LMC/SMC interactions within the past Gyr, particularly the SMC’s pericentric passage ∼150 Myr ago and a possible SMC crossing of the LMC disc plane ∼400 Myr ago, likely do not perturb stars that today comprise the arm. Historical interactions with the SMC prior to ∼1 Gyr ago may be required to explain some of the observed kinematic properties of the arm, in particular its strongly negative in-plane radial velocity.

 

ABSTRACT We present an overview of, and first science results from, the Magellanic Edges Survey (MagES), an ongoing spectroscopic survey mapping the kinematics of red clump and red giant branch stars in the highly substructured periphery of the Magellanic Clouds. In conjunction with Gaia astrometry, MagES yields a sample of ~7000 stars with individual 3D velocities that probes larger galactocentric radii than most previous studies. We outline our target selection, observation strategy, data reduction, and analysis procedures, and present results for two fields in the northern outskirts (>10° on-sky from the centre) of the Large Magellanic Cloud (LMC). One field, located in the vicinity of an arm-like overdensity, displays apparent signatures of perturbation away from an equilibrium disc model. This includes a large radial velocity dispersion in the LMC disc plane, and an asymmetric line-of-sight velocity distribution indicative of motions vertically out of the disc plane for some stars. The second field reveals 3D kinematics consistent with an equilibrium disc, and yields Vcirc = 87.7 ± 8.0 km s−1 at a radial distance of ~10.5 kpc from the LMC centre. This leads to an enclosed mass estimate for the LMC at this radius of (1.8 ± 0.3) × 1010 M⊙.