Extended high-ionization MgIV emission tracing widespread shocks in starbursts seen by JWST /NIRSpec

We report the detection of extended (>0. 5-1kpc) high-ionization MgIV 4. 487 m (80 eV) emission in four local luminous infrared galaxies observed with JWST/NIRSpec. Excluding the nucleus and outflow of the Type 1 active galactic nucleus (AGN) in the sample, we find that the MgIV luminosity is well correlated with that of H recombination lines, which mainly trace star forming clumps in these objects, and that the ArVI 4. 530 m (75 eV), usually seen in AGN, is undetected. On 100-400pc scales, the MgIV line profiles are broader (sigma (MgIV) =90 +- 25 km/s) and shifted (Deltaᵥ up to +- 50 km/s) compared to those of the H recombination lines and lower ionization transitions (e. g. , sigma (Hu-12) =57 +- 15 km/s). The MgIV kinematics follow the large scale rotating velocity field of these galaxies and the broad MgIV profiles are compatible with the broad wings detected in the H recombination lines. Based on these observational results, extended highly ionized gas more turbulent than the ambient interstellar medium, possibly as a result of ionizing shocks associated with star-formation, is the most likely origin of the MgIV emission. We also computed new grids of photoionization and shock models to investigate where the MgIV line originates. Shocks with velocities of 100-130 km/s reproduce the observed line ratios and the MgIV luminosity agrees with that expected from the mechanical energy released by supernove (SNe) in these regions. Therefore, these models support shocks induced by SNe as the origin of the MgIV line. Future studies on the stellar feedback from SNe will benefit from the MgIV line that is little affected by obscuration and, in absence of an AGN, can only be produced by shocks due to its high ionization potential.