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

Abstract

We present the detection of very extended stellar populations around the Large Magellanic Cloud (LMC) out to R similar to 21 degrees, or similar to 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 similar to 24) SMASH color-magnitude diagrams (CMDs) clearly reveal old (similar to 9 Gyr), metal-poor ([Fe/H] approximate to -0.8 dex) main sequence stars at a distance of similar to 50 kpc. The surface brightness of these detections is extremely low with our most distant detection at Sigma(g) approximate to 34 mag arcsec(-2). The SMASH radial density profile breaks from the inner LMC exponential decline at similar to 13 degrees -15 degrees and a second component at larger radii has a shallower slope with power-law index alpha = -2.2 that contributes similar to 0.4% of the LMC's total stellar mass. In addition, the SMASH densities exhibit large scatter around our best-fit model of similar to 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 approximate to 8 degrees) 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.