Left: [C II]/FIR map of HZ4. We have considered only rest-frame ∼160 μm dust continuum emission above the 2σ level. The color bar indicates the [C II]/FIR value. Right: [C II]/FIR ratio as a function of Σ_FIR in four kiloparsec-size regions extracted across the disk of HZ4 (orange circles and dashed black circles in the left panel). The error bars, mainly due to the uncertainty in the FIR luminosity, are shown in orange. For comparison, we show nearby star-forming and starburst galaxies from the SHINING sample (Herrera-Camus et al. 2018a), ∼100 pc scale regions in the central disk of M 82 in green (Contursi et al. 2013; Herrera-Camus et al. 2018a), and ∼400 pc scale regions in the central region of M 83 in purple. The solid gray line shows the best quadratic fit to the SHINING data (Herrera-Camus et al. 2018a).