ALMA Chemical Evolution (ACE) survey: the dust content of subsolar metallicity galaxies at cosmic noon

Abstract

Dust plays a key role in galaxy evolution by influencing star formation and shaping the observed spectrum of galaxies. However, at z~2 (cosmic noon) our knowledge of the dust mass budget is currently limited to the most massive, metal-rich systems, which are not representative of the bulk galaxy population. Here, we probe the lower mass, subsolar metallicity regime by measuring the dust mass of 25 galaxies at z~2.3 from the ALMA Chemical Evolution (ACE) Large Program. The sample contains star-forming galaxies in the COSMOS field with robust strong-line metallicities down to ~0.3 $Z_\odot$. Using the dust continuum emission detected at 873micron or 1.3mm we constrain the dust mass by assuming an optically thin single-temperature modified blackbody. The resulting dust masses average $10^{8}\,\mathrm{M}_\odot$, and they are three to nine times larger than those of z=0 galaxies at a matched metallicity and stellar mass. We also find positive correlations between dust mass and stellar mass, metallicity, and star formation rate (SFR). In contrast, we find that the $M_\mathrm{dust}/M_\mathrm{stars}$ (DtS) ratio scatters around $10^{-2.2}$ but shows no evidence of correlation with metallicity. This result is consistent with dust evolution models that predict a constant DtS once the ISM reaches the critical metallicity, at which metal accretion onto grains becomes the main mode of dust buildup. The correlation between $M_\mathrm{dust}/\mathrm{SFR}$ and metallicity also suggest that ACE galaxies have already surpassed the critical metallicity. Finally, we find that the DtS ratio is correlated to the specific SFR (sSFR). Since the sSFR are high ($> 10^{-8}\,\mathrm{yr}^{-1}$) this explains the DtS excess over z~0 galaxies. In turn, both sSFR and DtS are likely driven by the molecular gas fraction, as supported by CO(3-2) measurements taken as part of ACE.