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Arxiv: Extended high-ionization [MgIV] emission tracing widespread shocks in starbursts seen by JWST /NIRSpec Published: 4/25/2024 5:30:38 PM Updated: 4/25/2024 5:30:38 PM

Paper abstract: We report the detection of extended (>0.5-1kpc) high-ionization [MgIV] 4.487\mum (80 eV) emission in four local luminous infrared galaxies observed withJWST/NIRSpec. Excluding the nucleus and outflow of the Type 1 active galacticnucleus (AGN) in the sample, we find that the [MgIV] luminosity is wellcorrelated with that of H recombination lines, which mainly trace star formingclumps in these objects, and that the [ArVI] 4.530 \mum (75 eV), usually seenin AGN, is undetected. On 100-400pc scales, the [MgIV] line profiles arebroader (sigma([MgIV])=90 +- 25 km/s) and shifted (Delta_v 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 largescale rotating velocity field of these galaxies and the broad [MgIV] profilesare compatible with the broad wings detected in the H recombination lines.Based on these observational results, extended highly ionized gas moreturbulent than the ambient interstellar medium, possibly as a result ofionizing shocks associated with star-formation, is the most likely origin ofthe [MgIV] emission. We also computed new grids of photoionization and shockmodels to investigate where the [MgIV] line originates. Shocks with velocitiesof 100-130 km/s reproduce the observed line ratios and the [MgIV] luminosityagrees with that expected from the mechanical energy released by supernove(SNe) in these regions. Therefore, these models support shocks induced by SNeas the origin of the [MgIV] line. Future studies on the stellar feedback fromSNe will benefit from the [MgIV] line that is little affected by obscurationand, in absence of an AGN, can only be produced by shocks due to its highionization potential.