PI: Kimberly Herrmann, Penn State University, firstname.lastname@example.org
Address: Department 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 M74
Abstract: Our understanding of galaxy formation is severely limited by our lack of knowledge about the mass profiles of galaxies. We know that disk galaxies are surrounded by dark matter halos, but from rotation curves alone, it is impossible to decouple the gravitational contribution of a halo from that of the visible disk mass. Most analyses are therefore forced to rely on the ``maximal disk'' assumption, which requires that the mass-to-light ratio of a galactic disk 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 one galaxy, M33, has any data more than ~1.5 scale lengths from its nucleus. Its kinematic measurements extend to ~ 5 infrared disk scale lengths, and imply a matter scale length that is more than twice that inferred from K-band surface photometry. We propose to learn more about the distribution of disk mass in normal spiral galaxies by measuring the z-motions of planetary nebulae (PNe) in a sample of face-on spirals. This specific proposal is to image M74 in [O III] (lambda) 5007, off-band (lambda) 5290, H(alpha), and B, in order to identify a sample of \gtrsim 100 PNe for follow- up spectroscopy. This would allow us to measure the system's disk surface-density and mass-to-light ratio over \gtrsim 5 disk scale lengths, thereby constraining models of galactic dark halos. As a by- product, our M74 measurements will also produce the first precision distance estimate to the galaxy.
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