Low Surface Brightness Imaging of the Magellanic System: Imprints of Tidal Interactions Between the Clouds in the Stellar Periphery

Abstract

We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts of the stellar disk of the LMC (<10°from the LMC center). These data have higher resolution than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in the northern periphery, with no comparable counterparts in the south. We compare these data to detailed simulations of the LMC disk outskirts, following interactions with its low mass companion, the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field. The simulations are used to assess the origin of the northern structures, including also the low density stellar arc recently identified in the Dark Energy Survey data by Mackey et al. at ∼15°. We conclude that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to constrain the LMC's interaction history with and impact parameter of the SMC. More generally, we find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for 1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are driven by dwarf-dwarf interactions.

SMASH: Survey of the MAgellanic Stellar History

“…On our very successful 2016 February 13-18 run, we finished all of the fields around the MCs that were observable, and therefore, we decided to observe some "extra" shallow fields around the LMC that would help reveal structures in the LMC disk (similar to those seen by Mackey et al 2016 andBesla et al 2016) and allow us to use the field overlaps to create a more homogeneously calibrated data set around the LMC using an "übercal" technique (e.g., Padmanabhan et al 2008). Two 60 s exposures in griz with a half-chip dither between the pairs were obtained for these 40 fields (with field numbers between 184 and 243).…”

The Properties of the Magellanic Bridge Based on OGLE IV RR Lyrae Variables

“…If the older populations, such as RR Lyrae, follow the trends of their younger counterparts, it would give credence to tidal stripping (as in-situ formation is not likely at such an early time in the Bridge). However, if the distribution of RR Lyrae is smooth across the Bridge, it may be indicative of an extended halo distribution of the SMC and LMC overlapping in the Bridge (Besla et al 2016;Saha et al 2010).…”

“…The large velocity dispersion of these stars (σRV = 50 ± 2 km s −1 ) indicates a homogeneous, old, and metal-poor halo. Other recent work has offered star counts as evidence that the LMC disk may extend to ∼16 kpc (Saha et al 2010;Besla et al 2016). …”

Star cluster formation history along the minor axis of the Large Magellanic Cloud

“…Because of evidence of tidal interactions between the Magellanic Clouds (Besla et al 2016), the LMC could have experienced a much more complicated star-formation history than would be inferred simply by assuming a constant ratio of stars in clusters to those in the field (e.g., Geha et al 1998), and that significant spatial variations exist, particular when comparing the central bar to the disc (Smecker-Hane et al 2002;Harris & Zaritsky 2009). …”