The DiskMass Survey

VI. Gas and stellar kinematics in spiral galaxies from PPak integral-field spectroscopy^⋆,⋆⋆

¹ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
e-mail: verheyen@astro.rug.nl; westfall@astro.rug.nl
² Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
e-mail: martinsson@strw.leidenuniv.nl
³ Department of Astronomy, University of Wisconsin, 475 N. Charter St., Madison, WI 53706, USA
e-mail: mab@astro.wisc.edu; andrew@astro.wisc.edu
⁴ NRC Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, British Columbia, V9E 2E7, Canada
e-mail: david.andersen@nrc-cnrc.gc.ca
⁵ National Optical Astronomy Observatory, 950 North Cherry Ave., Tucson, AZ 85719, USA
e-mail: swaters@noao.edu

Received: 7 October 2012
Accepted: 9 May 2013

Abstract

We present ionized-gas ([Oiii]λ5007 Å) and stellar kinematics (velocities and velocity dispersions) for 30 nearly face-on spiral galaxies out to as many as three K-band disk scale lengths (h_R). These data have been derived from PPak integral-field-unit spectroscopy from 4980−5370 Å observed at a mean resolution of λ/Δλ = 7700 (σ_inst = 17 km s^-1). 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 and data reduction, including a robust measurement and removal of shift, scale, and rotation effects in the data due to instrumental flexure. Using an in-plane coordinate system determined by fitting circular-speed curves to our velocity fields, we derive azimuthally averaged rotation curves and line-of-sight velocity dispersion (σ_LOS) and luminosity profiles for both the stars and [Oiii]-emitting gas. 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 (h_σ) is 2h_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 1.5h_R, σ_LOS 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 (σ_z,0) and their circular rotational speed at 2.2h_R (V_2.2hR^Oiii), with a zero point indicating that galaxy disks are submaximal. Moreover, weak but consistent correlations exist between σ_z,0/V_2.2hR^Oiii and global galaxy properties 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.