Structure of the Large Magellanic Cloud from 2MASS

Abstract

We derive structural parameters and evidence for extended tidal debris from star count and prelimi-nary standard candle analyses of the Large Magellanic Cloud based on Two-Micron All-Sky Survey (2MASS) data. The full-sky coverage and low extinction in present an ideal sample for structural K s analysis of the LMC. The star count surface densities and deprojected inclination for both young and older populations are generally consistent with previous work. We Ðt the projected density with an expo-nential disk or spherical power-law model with an optional two-dimensional elliptical bar. The derived disk scale length is R \ 1.42 ^ 0.01 kpc for models without the bar and R \ 2.15 ^ 0.01 kpc for models with the bar included. The median value for the bar axis ratio is q \ 3.4 for intermediate and old LMC populations and q \ 4.1 for young populations. The radial proÐle shows evidence for disk truncation near 3 kpc. We use the full areal coverage and large " " LMC diameter ÏÏ/ " " Galactocentric ÏÏ distance ratio to infer the disk inclination based on perspective. The values for inclination derived from di erent popu-lations range from 22¡ to 29¡, with the variance weighted average The inclinations i \ 24¡ .0 ^ 0¡ .3. derived from models including the bar result in a larger estimate, A standard candle i \ 38¡ .2 ^ 0¡ .4. analysis based on a sample of carbon long-period variables (LPV) in a narrow color range, 1.6 \ allows us to probe the three-dimensional structure of the LMC along the line of sight. The J[K s \ 1.7, intrinsic brightness distribution of carbon LPVs in selected Ðelds implies that mag for this p M [ 0.2 color cut. The sample provides a direct determination of the LMC disk inclination : Distinct 42¡ .3 ^ 7¡ .2. features in the photometric distribution suggest several distinct populations. We interpret this as the pos-sible presence of an extended stellar component of the LMC, which may be as thick as 8 kpc, and inter-vening tidal debris at roughly 14 kpc from the LMC. Alternatively, these features may be intrinsic to asymptotic giant branch evolution and motivate additional theoretical modeling.