NOAO >   Observing Info >   Approved Programs >   2007A-0131

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Proposal Information for 2007A-0131


PI: Kimberly A. Herrmann, Penn State University, herrmann@astro.psu.edu
Address: Department of Astronomy and Astrophysics, 525 Davey Lab, University Park, PA 16802, USA

CoI: Robin Ciardullo, Penn State University

Title: The Planetary Nebula System of M94

Abstract: Our understanding of galaxy formation is severely limited by our lack of knowledge about the mass profiles of galaxies. Rotation curves reveal the presence of dark matter halos around disk galaxies, but the mass profiles of these halos cannot be decoupled from the visible disk mass using rotation curves alone. Most analyses therefore rely on the ``maximal disk'' hypothesis wherein the disk mass-to-light ratio (M/L) is assumed to be constant with radius. Absorption-line spectroscopy has shown that the constant M/L hypothesis is reasonable in a galaxy's inner regions. However, only recently have rotation curves farther out been decomposed into baryonic and dark matter components. Planetary nebula (PN) velocity measurements over the central ~6 disk scale lengths in M33 and M83 reveal flattened dispersion, indicating that the disks' M/Ls \bf increase by a factor of ~5 radially outward. PN velocity measurements over ~4 disk scale lengths in M31 are also consistent with a flattened dispersion (Merrett \etal 2006). We propose to continue studying the distribution of disk mass in normal spiral galaxies by measuring the vertical motions of planetary nebulae in nearby, face-on spirals. Last year, we used Hydra with WIYN to observe 52 PNe in M94. We now propose to use Hydra to measure the radial velocities of an additional 90 PNe so we may trace the system's disk surface mass density over ~6 disk scale lengths, and thereby better constrain models of galactic dark halos. We also plan to test color-M/L relations that have recently been used to decompose rotation curves.


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