Simulating the spatial distributions of gas- and ice-phase molecules in galaxies: a new method and preliminary results

Recent observations have revealed significant variations in the abundances of gas- and ice-phase molecules in galaxies with different luminosities and types. In order to discuss the physical origins of these variations, we incorporate gas- and dust-phase interstellar chemistry into galaxy-scale simulations with various baryonic physics including dust formation, evolution, and destruction, all of which are essential for the calculations of ≈400 interstellar molecule species. The new simulations can accordingly predict the abundances of gas- and ice-phase molecular species such as H2O and CO2 ice within individual molecular gas cloud of galaxies based on gas density and temperature, dust temperature (Tdust), elemental abundances (e.g. CHNOPS), UV radiation strength (FUV), and cosmic ray ionisation rate (ζCR) within the clouds. Since this is the first of the series of papers, we describe the details of the new simulations and present the preliminary results focused on the spatial distributions of H2O, CO, CO2, and CH3OH ice species in a disk galaxy similar to the Milky Way. We particularly discuss how Tdust and gas-phase elemental abundances can control the spatial distributions of the above molecules in galaxies. We briefly discuss the total amount of H2O and CO2 ices and radial distributions of PN and PO molecules in the Galaxy.