PI: Kimberly Herrmann, Penn State University, email@example.com
Address: Dept. of Astronomy and Astrophysics, 525 Davey Lab, University Park, PA 16802, USA
CoI: Robin Ciardullo, Penn State University
Title: The Planetary Nebula System of M74
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 the distribution of halo and visible disk mass 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 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 a 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 also reveal a flattened dispersion (Merrett \etal 2006). 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 M74 with the WIYN telescope and discovered ~ 250 PN candidates. We now propose to use Hydra to measure the PNe's radial velocities. This will enable us to trace the system's disk surface-mass density over ~ 4.4 scale lengths, and better constrain the radial profiles of the galaxy's dark halo. We also plan to test color-M/L relations that have recently been used to decompose rotation curves.
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