Observational [O/Fe]–sSFR relation compared with a broad range of theoretical expectations. Data points (big circles) were shifted to a common intermediate [O/Fe] baseline with additional offset due to possible oxygen dust depletion (Δ_d) included. This baseline provides the closest match to [O/Fe] of metal-poor dwarf stars in the MW from Amarsi et al. (2019) on the high sSFR end (which we use as a lower limit for the expected [O/Fe]_CCSN). The average [O/Fe] found in three sSFR bins is shown in the background (see caption of Fig. 7 and Table 1). Small grey data points were not used in the analysis as it is not clear how to consistently correct them for systematic offsets. The grey vertical band indicates the range of sSFR in which we expect the turnover based on the literature SN Ia DTD (see Fig. 2). Dark coloured ranges show the [O/Fe]–sSFR relations calculated with Eq. (1) for different SN Ia DTD and parameter choices. Left panel: power-law DTD with slope α_Ia = −1.1 and different minimum SN Ia delay times τ_Ia; min. Right panel: exponential DTD for two different values of the τ_Ia parameter. The coloured ranges span between the relations calculated with C_Ia/CC = 0.74 (upper edges) and C_Ia/CC = 2.5 (bottom edges) – see text for the details. We also plot the relations followed by TNG100-1-like galaxies (brown line, left panel) and EAGLE-like galaxies (turquoise line, right panel) and the average MW evolutionary track reconstructed with disc stars assuming constant star formation history (thick orange line, see Sect. 3.2).