Finally, the fraction of carbon fC in Fig. 9 shows very little variation in the gas-temperature diagram as it is typically of 10 %, except at the largest temperatures (T 107 K), where fC increases more significantly. This reflects the more efficient sputtering yields of silicate grains with respect to carbonaceous grains.

4.8. Effect of the metallicity We now explore how changing the metallicity of the gas affects the dust mass content in the galaxy. Figure 10 (top panel) shows the evolution of the DTM in the G10LG galaxy with different initial gas metallicities, sampling from 0.1, 0.3, 1 and 2 Z. There is no significant evolution of the gas metallicity for the two highest metallicity bins, while there is an increase to, respectively, 0.3 and 0.5 Z for the two lowest metallicity bins. The DTM shows a similar behaviour in all cases: a steep rise in 50-100 Myr that saturates to a steady state value that is larger for larger values of gas metallicity. This behaviour is naturally obtained by the scaling of dust accretion time with the inverse of the metallicity. However, by comparing the final value of the DTM with the Article number, page 14 of 30 Dubois et al.: Dust properties and extinction curves of simulated galaxies Z (ZO ) 0.2 0.2 0.1 time (Myr) 0 200 0.0 0.3 0.3 fC 0.0 DTM 0.5

1 0.4 0.4 2.0 fS 0.5 0.0 1.0 Z 2.5 100 1.5 300 0.5 2ZO ZO 0.3ZO 0.1ZO DTM 400 0 -1 (m-1) 10 0 10 20 30 40 50 rel. variation (%) 0 1 2 3 4 5 A/AV G10LG_VLZ G10LG_LZ G10LG G10LG_HZ MWLMCSMC 10 8 6 4 2 Fig. 10. Top panel: The dust-to-metal ratio (solid lines, left axis) and the gas metallicity (dashed lines, right axis) as a function of time for the 4 different initial metallicities of the G10LG galaxy: 0.1, 0.3, 1, and 2 Z (from bottom to top). Bottom panel: the fraction of carbonaceous grains (solid lines) and of small grains (dot-dashed lines). The DTM increases with metallicity, the fraction of carbonaceous grains increases with metallicity and the fraction of small grains decreases with metallicity.

Fig. 11. Comparison of extinction curves in the G10LG galaxy at time t = 400 Myr for different initial metallicities (Zg,0 = 0.1, 0.3, 1, and 2 Z for G10LG_VLZ, G10LG_LZ, G10LG, and G10LG_HZ respectively). The top panel shows the extinction curves, and the bottom panel shows the relative variation of the extinction curve with respect to the fiducial simulation G10LG. Galaxies with lower metallicities produce steeper UV-to-optical slopes due lower accretion efficiencies in the dense gas where coagulation proceeds, hence, the fraction of small grains is larger.