We study large-scale outflows in a sample of 96 star-forming galaxies at 1 \lesssim z \lesssim 2 , using near-UV spectroscopy of Fe ii and Mg ii absorption and emission .
The average blueshift of the Fe ii interstellar absorption lines with respect to the systemic velocity is -85 \pm 10 km s ^ { -1 } at z \sim 1.5 , with standard deviation 87 km s ^ { -1 } ; this is a decrease of a factor of two from the average blueshift measured for far-UV interstellar absorption lines in similarly selected galaxies at z \sim 2 .
The profiles of the Mg ii \lambda \lambda 2796 , 2803 lines show much more variety than the Fe ii profiles , which are always seen in absorption ; Mg ii ranges from strong emission to pure absorption , with emission more common in galaxies with blue UV slopes and at lower stellar masses .
Outflow velocities , as traced by the centroids and maximum extent of the absorption lines , increase with increasing stellar mass with 2–3 \sigma significance , in agreement with previous results .
We study fine structure emission from Fe ii* , finding several lines of evidence in support of the model in which this emission is generated by the re-emission of continuum photons absorbed in the Fe ii resonance transitions in outflowing gas .
In contrast , photoionization models indicate that Mg ii emission arises from the resonant scattering of photons produced in H ii regions , accounting for the differing profiles of the Mg ii and Fe ii lines .
A comparison of the strengths of the Fe ii absorption and Fe ii* emission lines indicates that massive galaxies have more extended outflows and/or greater extinction , while two-dimensional composite spectra indicate that emission from the outflow is stronger at a radius of \sim 10 kpc in high mass galaxies than in low mass galaxies .