The Disk Mass project; science case for a new PMAS IFU module

We present our Disk Mass project as the main science case for building a new fiber IFU-module for the PMAS spectrograph, currently mounted at the Cassegrain focus of the 3.5m telescope on Calar Alto. Compared to traditional longslit observations, the large light collecting power of 2-dimensional Integral Field Units dramatically improves the prospects for performing spectroscopy on extended low surface brightness objects with high spectral resolution. This enables us to measure stellar velocity dispersions in the outer disk of normal spiral galaxies. We describe some results from a PMAS pilot study using the existing lenslet array, and provide a basic description of the new fiber IFU-module for PMAS.