Molecular Composition of Local Dwarf Galaxies: Astrochemistry in Low-metallicity Environments

To investigate molecular composition of low-metallicity environments, we conducted spectral line survey observations in the 3mm band toward three dwarf galaxies, the Large Magellanic Cloud, IC 10, and NGC6822 with the Mopra 22 m, the Nobeyama 45m and the IRAM 30 m, respectively. The rotational transitions of CCH, HCN, HCO+, HNC, CS, SO, (CO)-C-13, and 12 CO were detected in all three galaxies. We found that the spectral intensity patterns are similar to one another regardless of star formation activities. Compared with Solar-metallicity environments, the molecular compositions of dwarf galaxies are characterized by (1) deficient nitrogen-bearing molecules and (2) enhanced CCH and suppressed CH3OH. These are interpreted (1) as a direct consequence of the lower elemental abundance of nitrogen, and (2) as a consequence of extended photon dominated regions in cloud peripheries due to the lower abundance of dust grains, respectively.