Exploring the Very Extended Low-surface-brightness Stellar Populations of the Large Magellanic Cloud with SMASH

We present the detection of very extended stellar populations around the Large Magellanic Cloud (LMC) out to R ~ 21°, or ~18.5 kpc at the LMC distance of 50 kpc, as detected in the Survey of the Magellanic Stellar History (SMASH) performed with the Dark Energy Camera on the NOAO Blanco 4 m Telescope. The deep (g ~ 24) SMASH color–magnitude diagrams (CMDs) clearly reveal old (~9 Gyr), metal-poor ([Fe/H] ≈ −0.8 dex) main-sequence stars at a distance of ~50 kpc. The surface brightness of these detections is extremely low with our most distant detection at Σ g ≈ 34 mag arcsec−2. The SMASH radial density profile breaks from the inner LMC exponential decline at ~13°–15° and a second component at larger radii has a shallower slope with power-law index α = −2.2 that contributes ~0.4% of the LMC's total stellar mass. In addition, the SMASH densities exhibit large scatter around our best-fit model of ~70% indicating that the envelope of stellar material in the LMC periphery is highly disturbed. We also use data from the NOAO Source catalog to map the LMC main-sequence populations at intermediate radii and detect a steep dropoff in density on the eastern side of the LMC (at R ≈ 8°) as well as an extended structure to the far northeast. These combined results confirm the existence of a very extended, low-density envelope of stellar material with a disturbed shape around the LMC. The exact origin of this structure remains unclear, but the leading options include an accreted halo or tidally stripped outer disk material.Funding for DES, including DECam, has been provided by the U.S. Department of Energy, National Science Foundation, Ministry of Education and Science (Spain), Science and Technology Facilities Council (UK), Higher Education Funding Council (England), National Center for Supercomputing Applications, Kavli Institute for Cosmological Physics, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo a Pesquisa, Conselho Nacional de Desenvolvimento Cient?fico e Tecnológico and the Ministério da Ciência e Tecnologia (Brazil), the German Research Foundation-sponsored cluster of excellence "Origin and Structure of the Universe" and the DES collaborating institutions.