PAH mass fraction (left) and luminosity fraction (right) as a function of stellar mass. Moving median (black curve) is shown for the robust q_PAH sample (see Section 2.2 for the definition of samples), and all galaxies are colour-coded by sSFR. In the left panel, horizontal lines show the median PAH mass fractions of z ∼ 0 galaxies with 12 + log(O/H) < 8.1 and > 8.1 from Draine et al. (2007). On the top x-axes, we also show the estimated metallicities from the O3N2-based mass-metallicity relation (MZR) of Topping et al. (2021) at z ∼ 1.5, and assuming the Pettini & Pagel (2004) calibration. The z ∼ 0.7 − 2 sample has a very similar q_PAH-metallicity behaviour to that inferred at z ∼ 0. Properties of the robust sample are in Table 1.