16209

Nebular emission lines in the far ultraviolet are rapidly drawing attention as quantitative diagnostics of nebular gas. In the coming decades comma they will be among the few information-carriers regarding the ionized ISM of faint galaxies at the highest redshifts. In particular comma the C IV 1550 AA and He II 1640 AA lines are very prevalent in low-metallicity dwarf starbursts. However when using them to estimate the conditions in the ISM comma C IV and He II diagnostics provide degenerate solutions between photo- and shock-ionization scenarios. Here we propose to obtain emission line images of two nearby starburst galaxies with the strongest emission in He II recombination line and C IV 1550 AA doublet. This will be the first C IV emission imaging ever performed. The targets are well-known low-metallicity starbursts comma and analogs of galaxy building blocks at the highest redshifts. We will measure the C IV and He II light profile comma and compute the total C IV (large-aperture) luminosity for the first time. Most importantly we will map line ratios involving C IV comma He II comma and H-alpha at virgul20 pc resolution comma while state-of-the-art modeling will derive the ionizing output of the star clusters. Hence we will directly couple stellar parameters to nebular diagnostics on the requisite spatial scales. Our results will determine the impact of photoionization and shocks to UV line diagnostics comma which will be pivotal for understanding the ISM conditions of the earliest galaxies.