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

DYNAMO is a multiwavelength, 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 Hα luminosities of >10⁴² erg s^-1, the typical lower limit for resolved spectroscopy at z ≃ 2. The sample covers a range in stellar mass (10⁹-10¹¹ M_⊙) and star formation rate (0.2-100 M_⊙ yr^-1). In this first paper of a series, we present integral-field spectroscopy of Hα 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 M_⊙ yr^-1, 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^-1, and V/σ 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 per cent 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<sub>⊙</sub> yr<sup>-1</sup>, 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/σ) 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.