PI: Kimberly A. Herrmann, Lowell Observatory, email@example.com
Address: 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA
CoI: Robin Ciardullo, Penn State University
Title: The Stellar Kinematics of Outer Disks: Evidence for Halo Substructure?
Abstract: \centerlineLook at a spiral; what do you see? Stars zooming `round in the galaxy! \centerlineTheir motions indicate total mass, but how much is DM, stars, and gas? \centerlineStudy motions in and out; first find monochromatic stars- that's my kind. \centerlineFind us, get our velocities, then: determine disk mass! I'm a PN! Rotation curves indicate the total mass of spirals, but halo mass profiles cannot be decoupled from the visible disk mass using rotation curves alone. To break this disk-halo degeneracy, we have been using planetary nebulae (PNe) to measure \sigma_z, the z-component of the stellar velocity dispersion, for the disks of face-on spirals. These measurements of \sigma_z, coupled with straightforward assumptions, have yielded disk surface mass estimates over several scale lengths (h_R) in 6 spirals. We find that in general while the inner ~3h_R of spiral galaxies have a constant mass-to-light ratio (M/L), \sigma_z in the outer disks is roughly flat with radius. This could be evidence for an increasing disk M/L, the presence of additional luminosity at large radii, disk flaring, or the existence of discrete cold-dark-matter subhalos which heat the disk. We propose to use the Mosaic wide-field imager to extend our PN survey to the extreme outer disk of M101 and to find PNe in the edge-on galaxy NGC 4565 to study the scale height of PNe, a parameter we cannot measure in our face- on spirals. For the past two years we have proposed to image M101 with the wide-field Mosaic camera on the KPNO 4-m telescope. Clouds prevented us the first year and we were not given time last year even though the TAC considered the study ``well worth completing.''
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