Measuring Galaxy Disk Mass with the SparsePak Integral Field Unit on WIYN

We present first results from the commissioning data of the SparsePak Integral Field Unit on the WIYN telescope. SparsePak is a bundle of 82 fibers, arranged in a sparsely filled, 76 x 77 arcsec hexagonal grid. It pipes light from one of the Nysmith foci to the Bench Spectrograph. See http://www.astro.wisc.edu/~mab/research/sparsepak and Bershady et al. (2002a) for more details. The fibers are each 5 arcsec in diameter and are thus suitable to obtain spectroscopy on extended objects of lower surface brightness such as galaxy disks. In fact, SparsePak was purposely developed to measure stellar kinematics and velocity dispersions in disk galaxies with the ultimate goal of constraining the surface densities and masses of stellar disks. Such a measurement is crucial to improve our understanding of the principal dynamical components in disk galaxies from rotation curve decompositions.