Molecular line emission in NGC 1068 imaged with ALMA - II. The chemistry of the dense molecular gas

摘要: Aims. We present a detailed analysis of Atacama Large Millimeter/submillimeter Array (ALMA) Bands 7 and 9 data CO, HCO+, HCN, CS, augmented with Plateau de Bure Interferometer (PdBI) the ~200 pc circumnuclear disc (CND) ~1.3 kpc starburst ring (SB ring) NGC 1068, nearby (D = 14 Mpc) Seyfert 2 barred galaxy. aim to determine physical characteristics dense gas in CND, establish whether different line intensity ratios we find within as well between CND SB ring, are due excitation effects (gas density temperature differences) or chemistry. Methods. estimate column densities each species local thermodynamic equilibrium (LTE). then compute large one-dimensional, non-LTE radiative transfer grids (using RADEX) by using only CO transitions first, all available molecules constrain densities, temperatures, CND. finally preliminary set chemical models origin gas. Results. that, general, is very (>105 cm-3) hot (T> 150 K), differences especially across The AGN position has lowest CO/HCO+, CO/HCN, CO/CS ratios. RADEX analyses seem indicate that there differentiation also chemistry some regions CND; much colder less than Chemical modelling does not succeed reproducing molecular one model per region, suggesting presence multi-gas phase components. Conclusions. LTE, RADEX, more gas-phase component necessary uniquely fit A higher number at ALMA resolution quantitatively these components.