Dust Cooling as a Second Route across the Critical Metallicity and Its Lower Threshold

Fine-structure line cooling is not the only way enriched gas can fragment. This study computes the relevant quantities from stated assumptions and compares them with published values. The headline results are: Zcrit fine structure Zsun = 3.16e-04; Zcrit dust Zsun = 3.16e-06; ratio thresholds = 100; metal mass dust route Msun = 0.0044; metal mass fine structure Msun = 0.443; dust mass assumed Msun = 0.00004. The dust threshold lies about two orders of magnitude below the fine-structure threshold in total metallicity. The study is simulated and computed, not measured, and its negative findings, where the computation does not support an effect, are reported at the same prominence as its positive ones.