2022ApJ...936...77S

We image the spatial extent of a cool galactic outflow with fine-structure Fe II* emission and resonant Mg II emission in a gravitationally lensed star-forming galaxy at z = 1.70347. The Fe II* and Mg II (continuum-subtracted) emissions span out to radial distances of ∼14.33 and 26.5 kpc, respectively, with maximum spatial extents of ∼21 kpc for Fe II* emission and ∼30 kpc for Mg II emission. Mg II emission is patchy and covers a total area of ∼184 kpc², constraining the minimum area covered by the outflowing gas to be ∼13% of the total area. Mg II emission is asymmetric and shows ∼21% more extended emission along the decl. direction. We constrain the covering fractions of the Fe II* and Mg II emission as a function of radial distance and characterize them with a power-law model. The Mg II 2803 emission line shows two kinematically distinct emission components and may correspond to two distinct shells of outflowing gas with a velocity separation of Δv ∼ 400 km s^–1. By using multiple images with different magnifications of the galaxy in the image plane, we trace the Fe II* and Mg II emissions around three individual star-forming regions. In all cases, both the Fe II* and Mg II emissions are more spatially extended compared to the star-forming regions traced by the [O II] emission. These findings provide robust constraints on the spatial extent of the outflowing gas and, combined with outflow velocity and column density measurements, will give stringent constraints on mass-outflow rates of the galaxy.