Measuring Galaxy Disk Mass with the SparsePak Integral Field Unit on WIYN
We present first results from commissioning data of the SparsePak Integral Field Unit on the WIYN telescope. SparsePak is a bundle of 82 fibers, each 5 arcsec in diameter and arranged in a sparsely filled, 76x77 arcsec hexagonal grid. NGC 3982, a nearly face-on, blue and very high surface brightness galaxy, was mapped in three spectral regions; around 5130A (MgI), 6680A (H-alpha) and 8660A (CaII-triplet) with FWHM spectral resolutions of 24, 16 and 37 km/s respectively. At 3.5 disk scale lengths, the spectra of 18 fibers were averaged after deprojection of the rotation curve. Stellar velocity dispersions were determined in the CaII region by convolving the spectrum of a K0.5-III template star with a Gaussian of varying FWHM and finding the best match to the azimuthally avaraged galaxy spectra. A radial mass surface density profile has been derived for a variety of scale heights assuming an isothermal vertical density profile. At two disk scale lengths, the mass surface density of N3982 is ~3 times higher than that of the Milky Way in the solar neighborhood. Surprisingly, the stellar rotation curve of this compact and high surface brightness galaxy is substantially sub-maximum.