AAS 207th Meeting, 8-12 January 2006
Session 188 Galaxy Anatomy: from Bars to Halos
Poster, Thursday, 9:20am-4:00pm, January 11, 2006, Exhibit Hall

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[188.11] Studies of Face-On Spiral Galaxies: Is the Disk Mass-to-Light Ratio Constant?

K. A. Herrmann, R. Ciardullo (Penn State)

When astronomers study dark matter halos of spiral galaxies, they typically assume that the disk mass-to-light ratio is *constant*. The best way to test this assumption is to determine the disk mass *directly* by measuring the velocity dispersion in the direction perpendicular to the plane of face-on spiral galaxies. We have been using planetary nebulae (PNe) as test particles in the outer regions of nearby spiral galaxies such as M33 and M83. Our first results for the PNe of M33 indicate that the mass-to-light ratio actually *increases* by more than a factor of 5 from the inner to the outer regions. Unfortunately, difficulties in identifying PNe in the inner regions of the galaxies limit the analysis in the central regions. However, integral field spectroscopy should be an excellent method to probe the inner regions and complete the analysis throughout an entire galaxy.

This work is supported by NSF grant AST 00-71238 and a PA Space Grant Fellowship.

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