The DiskMass Survey

Abstract

We present ionized-gas (OIII) and stellar kinematics (velocities and velocity\ndispersions) for 30 nearly face-on spiral galaxies out to as much as three disk\nscale lengths (h_R). These data have been derived from PPak IFU spectroscopy\n(4980-5370A), observed at a mean resolution of R=7700 (sigma_inst=17km/s).\nThese data are a fundamental product of our survey and will be used in\ncompanion papers to, e.g., derive the detailed (baryonic+dark) mass budget of\neach galaxy in our sample. Our presentation provides a comprehensive\ndescription of the observing strategy, data reduction, and analysis. Along with\na clear presentation of the data, we demonstrate: (1) The OIII and stellar\nrotation curves exhibit a clear signature of asymmetric drift with a rotation\ndifference that is 11% of the maximum rotation speed of the galaxy disk,\ncomparable to measurements in the solar neighborhood in the Milky Way. (2) The\ne-folding length of the stellar velocity dispersion is two times h_R on\naverage, as expected for a disk with a constant scale height and mass-to-light\nratio, with a scatter that is notably smaller for massive,\nhigh-surface-brightness disks in the most luminous galaxies. (3) At radii\nlarger than 1.5 h_R, the stellar velocity dispersion tends to decline slower\nthan the best-fitting exponential function, which may be due to an increase in\nthe disk mass-to-light ratio, disk flaring, or disk heating by the dark-matter\nhalo. (4) A strong correlation exists between the central vertical stellar\nvelocity dispersion of the disks and their circular rotational speed at 2.2\nh_R, with a zero point indicating that galaxy disks are submaximal. Moreover,\nweak but consistent correlations exist such that disks with a fainter central\nsurface brightness in bluer and less luminous galaxies of later morphological\ntypes are kinematically colder with respect to their rotational velocities.\n