High velocity outflows from young star-forming galaxies in the UKIDSS Ultra-Deep Survey

Abstract: We investigate galactic-scale outflows in the redshift range 0.71 < z < 1.63, using 413 K-band selected galaxies observed in the spectroscopic follow-up of the UKIDSS Ultra-Deep Survey (UDSz). The galaxies have an average stellar mass of ~10^9.5 solar masses and span a wide range in rest-frame colours, representing typical star-forming galaxies at this epoch. We stack the spectra by various galaxy properties, including stellar mass, [OII] equivalent width, star-formation rate, specific star-formation rate and rest-frame spectral indices. We find that outflows are present in virtually all spectral stacks, with velocities ranging from 100-1000 km s^-1, indicating that large-scale outflowing winds are a common property at these redshifts. The highest velocity outflows (>500 km s^-1) are found in galaxies with the highest stellar masses and the youngest stellar populations. Our findings suggest that high velocity galactic outflows are mostly driven by star-forming processes rather than AGN, with implied mass outflow rates comparable to the rates of star formation. Such behaviour is consistent with models required to reproduce the high-redshift mass-metallicity relation.