Exploring the Very Extended Low Surface Brightness Stellar Populations of the Large Magellanic Cloud with SMASH

TL;DR

This study detects and characterizes an extremely extended, low-density stellar envelope around the Large Magellanic Cloud, revealing its disturbed shape and potential origins through deep imaging and density profile analysis.

Contribution

First detailed mapping of the LMC's extended stellar populations out to 18.5 kpc, showing a disturbed, low-density envelope with implications for its formation history.

Findings

Detection of old, metal-poor stars at 50 kpc from LMC center.

Identification of a shallow, power-law stellar envelope beyond 13-15 degrees.

Evidence of a highly disturbed stellar envelope with large density scatter.

Abstract

We present the detection of very extended stellar populations around the Large Magellanic Cloud (LMC) out to R~21 degrees, 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 4m 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 having 34 mag per arcsec squared in g-band. The SMASH radial density profile breaks from the inner LMC exponential decline at ~13-15 degrees and a second component at larger radii has a shallower slope with power-law index of -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 deg) 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 disturbed shape around the LMC. The exact origin of this structure remains unclear but the leading options include a classical accreted halo or tidally stripped outer disk material.