METAL-Z: Metal Evolution, Transport, and Abundance at Low Metallicity (Z)
Abstract
A key component of the baryon cycle is the depletion of metals between the gas and dust phases in the neutral ISM. Our understanding of the dust and gas contents of galaxies via dust emission-based gas mass estimates and of the chemical enrichment of the Universe via spectroscopy of damped lyman-alpha systems (DLAs) critically relies on the characterization of the variations of the dust-to-metal mass ratio (D/M) with environment (metallicity, density, morphology). This understanding must be built in the nearby universe, where both gas-phase abundances and photospheric abundances of young stars recently formed out of the ISM can be measured. We propose to obtain COS G130M spectra toward 14 massive stars in IC 1613 (Z=0.15 Z_sun) and Sextans-A (Z=0.08 Z_sun), lower than the critical metallicity at which chemical evolution models predict D/M decreases steeply with metallicity. The COS spectra will be used to derive interstellar depletions of iron and sulfur, from which D/M and the dust-to-gas mass ratio (D/G) will be inferred. Combined with depletion measurements available in the Milky Way, LMC (0.5 Z_sun), and SMC (0.2 Z_sun), we will be able for the first time to measure depletions, D/G, and D/M as a function of metallicity down to 0.08 Z_sun, and enable a comprehensive characterization of the lifecycle of metals in neutral gas and dust in galaxies, thereby observationally addressing important questions about chemical enrichment and galaxy evolution. In particular, this program will provide the depletion calibrations required to interpret DLA metallicity measurements, and substantially improve the accuracy of dust-based gas-mass estimates at low and high redshift.
- Publication:
-
HST Proposal
- Pub Date:
- June 2019
- Bibcode:
- 2019hst..prop15880R