The properties of the star-forming interstellar medium at<i>z</i> = 0.84-2.23 from HiZELS: mapping the internal dynamics and metallicity gradients in high-redshift disc galaxies

Abstract

We present adaptive optics assisted, spatially resolved spectroscopy of a sample of nine H�-selected galaxies at z =0.84–2.23 drawn from the HiZELS narrow-band survey.&#13;\nThese galaxies have star-formation rates of 1–27M⊙ yr−1 and are therefore representative of the typical high-redshift star-forming population. Our �kpc-scale resolution&#13;\nobservations 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&#13;\nthe 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&#13;\nperiod. Together, these demonstrate a change in mass-to-light ratio in the B-band of �(M/ LB) / (M/ LB)z=0 �3.5 between z =1.5 and z =0, with most of the evolution occuring below z =1. We also use the spatial variation of [Nii] /H� to show that the metallicity of the ionised gas in these galaxies declines monotonically with galactocentric radius, with an average �log(O/H) /�R=−0.027±0.005 dex kpc−1. This gradient is consistent with predictions for high-redshift disk galaxies from cosmologically based hydrodynamic simulations.&#13;\nKey words: galaxies: evolution – galaxies: formation – galaxies: high-redshift