NOAO >   Observing Info >   Approved Programs >   2006A-0147

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Proposal Information for 2006A-0147


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

CoI: Robin Ciardullo, Penn State University
CoI: George Jacoby, WIYN Observatory
CoI: John Feldmeier, NOAO

Title: The Planetary Nebula System of M94

Abstract: Our understanding of galaxy formation is severely limited by poorly known galaxy mass profiles. Rotation curves reveal dark matter halos around disk galaxies, but halo and visible disk mass profiles cannot be decoupled using rotation curves alone. Most analyses therefore rely on the ``maximal disk'' method that assumes the disk mass-to-light ratio (M/L) is constant with radius. Absorption-line spectroscopy has shown that the constant M/L hypothesis is reasonable in a galaxy's inner regions. However, only two galaxies have data more than ~ 1.5 scale lengths from their nuclei: M33 and M83. Planetary nebula (PN) velocity measurements over the central ~ 6 disk scale lengths in M33 indicate that the galaxy's disk M/L increases by a factor of ~ 5 radially outward. Preliminary PN results for M83 also suggest a varying disk M/L. We propose to study the distribution of disk mass in normal spiral galaxies by measuring the z-motions of PNe in nearby, face-on systems. Last year, we conducted an [O III] (lambda) 5007 survey of M94 with the WIYN telescope and discovered ~ 200 PN candidates. We now propose to use Hydra to measure the PN radial velocities so we may trace the system's disk surface-mass density over ~ 6 scale lengths, and thereby better constrain the radial profiles of the galaxy's dark halo.


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