DYNAMO - I. A sample of H -luminous galaxies with resolved kinematics

DYNAMO is a multi-wavelength, spatially-resolved survey of local (z 0:1) star-forming galaxies designed to study evolution through comparison with samples at z ' 2. Half of the sample has integrated H luminosities of > 1042 erg/s, the typical lower limit for resolved spectroscopy at z~2. The sample covers a range in stellar mass (109-1011 Msun) and star-formation rate (0.2-100 Msun/yr). In this first paper of a series, we present integral-field spectroscopy of H-alpha emission for the sample of 67 galaxies. We infer gas fractions in our sample as high as ~0.8, higher than typical for local galaxies. Gas fraction correlates with stellar mass in galaxies with star-formation rates below 10 Msun/yr, as found by COLDGASS, but galaxies with higher star-formation rates have higher than expected gas fractions. There is only a weak correlation, if any, between gas fraction and gas velocity dispersion. Galaxies in the sample visually classified as disc-like are offset from the local stellar-mass Tully-Fisher relation to higher circular velocities, but this offset vanishes when both gas and stars are included in the baryonic Tully-Fisher relation. The mean gas velocity dispersion of the sample is ~50 km/s, and V/sigma ranges from 2 to 10 for most of the discs, similar to 'turbulent' galaxies at high redshift. Half of our sample show disc-like rotation, while ~20 percent show no signs of rotation. The division between rotating and non-rotating is approximately equal for the sub-samples with either star-formation rates > 10 M yr⊙1, or specific-star-formation rates typical of the star-formation ‘main sequence' at star-formation rates > 10 M yr⊙1, or specific-star-formation rates typical of the star-formation ‘main sequence' at z ' 2. Across our whole sample, we find good correlation between the dominance of ‘turbulence' in galaxy discs (as expressed by V= ) and gas fraction as has been predicted for marginally stable Toomre discs. Comparing our sample with many others at low- and high-redshift reveals a correlation between gas velocity dispersion and star formation rate. These findings suggest the DYNAMO discs are excellent candidates for local galaxies similar to turbulent z ' 2 disc galaxies.