The DiskMass Survey

Abstract

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