The Properties of the Star-Forming Interstellar Medium at z=0.84-2.23 from HiZELS - I: Mapping the Internal Dynamics and Metallicity Gradients in High-Redshift Disk Galaxies

Abstract: We present adaptive optics assisted, spatially resolved spectroscopy of a sample of nine H-alpha-selected galaxies at z=0.84--2.23 drawn from the HiZELS narrow-band survey. These galaxies have star-formation rates of 1-27Mo/yr and are therefore representative of the typical high-redshift star-forming population. Our ~kpc-scale resolution observations show that approximately half of the sample have dynamics suggesting that the ionised gas is in large, rotating disks. We model their velocity fields to infer the inclination-corrected, asymptotic rotational velocities. We use the absolute B-band magnitudes and stellar masses to investigate the evolution of the B-band and stellar mass Tully-Fisher relationships. By combining our sample with a number of similar measurements from the literature, we show that, at fixed circular velocity, the stellar mass of star-forming galaxies has increased by a factor 2.5 between z=2 and z=0, whilst the rest-frame B-band luminosity has decreased by a factor ~6 over the same period. Together, these demonstrate a change in mass-to-light ratio in the B-band of Delta(M/L_B)/(M/L_B)_(z=0) \sim 3.5 between z=1.5 and z=0, with most of the evolution occurring below z=1. We also use the spatial variation of [NII]/Halpha to show that the metallicity of the ionised gas in these galaxies declines monotonically with galacto-centric radius, with an average Delta(log O/H)/DeltaR=-0.027+/-0.005dex/kpc. This gradient is consistent with predictions for high-redshift disk galaxies from cosmologically based hydrodynamic simulations.