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Dust and Stellar Populations in the Large Magellanic Cloud

We present an analysis of line-of-sight extinction measurements obtained using 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 larger by several tenths of a magnitude for stars with effective temperatures greater than 12,000 K than for stars with effective temperatures between 5500 and 6500 K. Several repercussions of this population-dependent extinction are discussed. In particular, LMC distance measurements that utilize old stellar populations, but use extinctions derived from OB stars, may be biased low. As a specific example, we show that the LMC distance modulus derived from field red clump stars is revised upward relative to published measurements by ∼0.2 mag if one uses the extinction measured for a matched stellar population. Conversely, measurements that utilize the youngest stars are subject to greater, and more variable, extinction leading preferentially to results that may be biased high. Population-dependent extinction affects the interpretation of color-magnitude diagrams and results in an effective absorption law that is steeper than that intrinsic to the dust for unresolved stellar systems. We further explore the relation between the stellar populations and dust by comparing our extinction map to the 100 μm image of the region and identifying potential heating sources of the dust. We find that although regions of high 100 μm flux are associated with young stars, young stars are not necessarily associated with regions of high 100 μm flux and that ∼50% of the 100 μm flux is emitted beyond the immediate regions of high OB stellar density. We conclude that 100 μm flux should be used with caution as a star formation tracer, particularly 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 (which is twice that of the OB stars; Harris, Zaritsky, & Thompson).