  The cycling of metals between interstellar gas and dust is a critical aspect
of the baryon cycle of galaxies, yet our understanding of this process is
limited. This study focuses on understanding dust depletion effects in the low
metallicity regime (< 20% Zo) typical of cosmic noon. Using medium-resolution
UV spectroscopy from the COS onboard the Hubble Space Telescope, gas-phase
abundances and depletions of iron and sulfur were derived toward 18 sightlines
in local dwarf galaxies IC 1613 and Sextans A. The results show that the
depletion of Fe and S is consistent with that found in the Milky Way, LMC and
SMC. The depletion level of Fe increases with gas column density, indicating
dust growth in the interstellar medium (ISM). The level of Fe depletion
decreases with decreasing metallicity, resulting in the fraction of iron in gas
ranging from 3% in the MW to 9% in IC 1613 and ~19% in Sextans A. The
dust-to-gas and dust-to-metal ratios (D/G, D/M) for these dwarf galaxies were
estimated based on the MW relations between the depletion of Fe and other
elements. The study finds that D/G decreases only slightly sub-linearly with
metallicity, with D/M decreasing from 0.41 +/- 0.05 in the MW to 0.11 +/- 0.11
at 0.10 Zo (at log N(H) = 21 cm-2). The trend of D/G vs. metallicity using
depletion in local systems is similar to that inferred in Damped Ly-alpha
systems from abundance ratios but lies higher than the trend inferred from FIR
measurements in nearby galaxies.
