The velocity structure of large magellanic cloud carbon stars: Young disk, old disk, and perhaps a separate population

We analyze the velocity residuals of 551 carbon stars relative to a rotating-disk model of the inner similar to 70 deg(2) of the Large Magellanic Cloud (LMC). We find that the great majority of the stars in this sample are best fitted as being due to two different populations, a young disk population containing 20% of the stars with a velocity dispersion of 8 km s(-1) and an old disk containing the remaining stars with a velocity dispersion of 22 km s(-1). The young disk population has a metallicity similar to 0.25 dex higher than that of the old disk. With less certainty, the data also suggest at the 2 delta level that there may be a third kinematically distinct population that is moving toward us at 30 km s(-1) relative to the LMC, consistent with measurements of 21 cm velocities. If real, this population contains about 7% of the carbon stars in the sample. It could be a feature in the disk of the LMC, or it could be tidal debris in the foreground or background. If it is tidal debris, this population could account for some or all of the microlensing events observed toward the LMC.