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Session 88 - Structure and Kinematics of Galaxies.
Oral session, Wednesday, January 17
La Condesa, Hilton
Near infrared light at 2 \mu m is relatively insensitive to the presence of hot young stars and dust in galaxies, and there has been recent interest in using it as a mass tracer in spiral galaxies. We present two related projects to test the fidelity of NIR light as a mass tracer.
First, we compare the strength of the gravity-sensitive 2.3 \mu m CO absorption feature in high and low surface brightness regions of the spiral galaxy NGC 1309. We find that the CO absorption is stronger in bright regions. We interpret this as evidence that young, luminous red supergiant stars contribute a large fraction of the NIR light in these regions. It follows that the bright patches in the NIR image of NGC 1309 may tell us more about its recent star formation history than about the underlying distribution of its old stellar population.
Second, we discuss a method for identifying giant stars in optical-infrared color-magnitude diagrams of Galactic plane star fields. Because most giant stars are dynamically old, they are representative of the population that dominates our Galaxy's disk mass. By comparing our giant star counts to the near infrared DIRBE (Diffuse Infrared Background Experiment) maps, we can see whether diffuse infrared light is a good tracer of giant stars, and hence of the old stellar mass component. Additionally, we discuss the prospects for studying Galactic structure directly using giant stars identified by our method.
Program listing for Wednesday