Chemodynamical properties of gas-rich galaxies: A comparison of observations and simulations

We performed a comprehensive analysis of the chemical and dynamical properties of quasar-damped Lyman-α (DLA) galaxies and compare these to the GEAR chemodynamical simulations. Specifically, we aim to constrain the behavior of α-element enhancements with metallicity, the dependence of [α/Fe] on the specific star formation rate (sSFR), and the absorption-line velocity widths (Δv90) versus stellar mass, Δv90 versus metallicity, and mass–metallicity relations. For the comparison, we selected five galaxies simulated with the chemodynamical Tree-SPH code GEAR with stellar masses in the range of 6.1 ≤ log M★/M⊙ ≤ 10.8 and at six different redshifts between 0.33 and 4.12. We find that the abundance ratios [α/Fe] and [M/H] observed in the interstellar medium (ISM) of DLA galaxies overlap with the abundance trends in gas of the simulated galaxies. Our findings corroborate a picture in which DLAs with Δv90 below and above 100 km s−1 trace galaxies with masses in the ranges of 6 < log M★ < 8 and 8 < log M★ < 11, respectively. We suggest that observations should be used with caution when constraining the theoretical [α/Fe] versus sSFR relations because of systematics (if abundances are obtained from emission lines) or differences in the gas properties as probed by a DLA and its counterpart. So far, only the observations in absorption of inner gas of the LMC and SMC are in agreement with the simulated data. We confirm that DLAs detected at large impact parameters most likely probe the gas of satellite or other halo galaxies which are adjacent to the central galaxy. We further find that the velocity widths versus stellar masses and mass–metallicity relations agree well with observations, while GEAR should be calibrated more carefully to reproduce the Δv90 versus metallicity relation. To place our results in context, we additionally incorporated chemodynamical properties of a few selected model galaxies obtained from other simulations.