PI: Kimberly A. Herrmann, Penn State University, firstname.lastname@example.org
Address: Dept. of Astronomy and Astrophysics, 525 Davey Lab, University Park, PA 16802, USA
CoI: Robin Ciardullo, Penn State University
Title: The Stellar Kinematics of Outer Disks: Evidence for Halo Substructure?
Abstract: Our understanding of galaxy formation is limited by our weak knowledge of galactic mass profiles. Rotation curves reveal dark matter halos around 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 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 in 6 spiral galaxies. Our survey has produced an interesting result: while the inner ~3 disk scale lengths of spiral galaxies have a constant mass-to- light ratio (consistent with a maximal-disk), \sigma_z in the outer disks is roughly flat with radius. This could be evidence for an increasing disk mass-to-light ratio, the presence of additional luminosity at large radii, or the existence of discrete cold-dark-matter subhalos which heat the disk. We propose to investigate this phenomenon further by extending our PN survey to the extreme outer disks of two galaxies: M74 and IC 342. This proposal is to image the galaxies with the wide-field Mosaic camera on the KPNO 4-m telescope. If this imaging is successful, we will then propose follow-up spectroscopy with WIYN/Hydra. At this time, we are also proposing to improve our knowledge of the disks' stellar content and surface brightness profile by performing J H Ks imaging with NEWFIRM.
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