Dust and stellar populations in the Large Magellanic Cloud

We present an analysis of line-of-sight extinction measurements obtained us ing data from the Magellanic Clouds Photometric Survey (Zaritsky, Harris, & Thompson), which provides four-filter photometry for millions of stars in the Large Magellanic Cloud. We find that visual extinctions are typically l arger by several tenths of a magnitude for stars with effective temperature s greater than 12,000 K than for stars with effective temperatures between 5500 and 6500 K. Several repercussions of this population-dependent extinct ion are discussed. In particular, LMC distance measurements that utilize ol d stellar populations, but use extinctions derived from OB stars, may be bi ased low. As a specific example, we show that the LMC distance modulus deri ved from field red clump stars is revised upward relative to published meas urements by similar to 0.2 mag if one uses the extinction measured for a ma tched stellar population. Conversely, measurements that utilize the younges t stars are subject to greater, and more variable, extinction leading prefe rentially to results that may be biased high. Population-dependent extincti on affects the interpretation of color-magnitude diagrams and results in an effective absorption law that is steeper than that intrinsic to the dust f or unresolved stellar systems. We further explore the relation between the stellar populations and dust by comparing our extinction map to the 100 mu m image of the region and identifying potential heating sources of the dust . We find that although regions of high 100 mu m flux are associated with y oung stars, young stars are not necessarily associated with regions of high 100 mu m flux and that similar to 50% of the 100 mu m flux is emitted beyo nd the immediate regions of high OB stellar density. We conclude that 100 m u m flux should be used with caution as a star formation tracer, particular ly for studies of star formation within galaxies. Finally, we reproduce the observed extinction variation between the hot and cold stellar populations with a simple model of the distribution of the stars and dust in which the scale height of the cooler stars is much greater than that of the dust (wh ich is twice that of the OB stars; Harris, Zaritsky, & Thompson).