2021MNRAS.504.5941T

Multiple molecular lines are useful for studying the physical properties of multiphase star-forming gas in different types of galaxies. We probe the molecular gas throughout the disc of the spiral galaxy NGC 5033, hosting an active galactic nucleus (AGN), using multiple low-J CO lines [¹²CO(1-0, 2-1, 3-2 and ¹³CO(1-0, 2-1)] and dense gas tracers [HCN(1-0) and HCO⁺(1-0)]. First, we determine the ratios of the integrated intensity maps and the ratio of intensities in position velocity diagrams. Secondly, we obtain the ratios of CO lines and high-density tracers at the centre; and thirdly, we model these line ratios using a radiative transfer code. Line ratio diagnostics reveal that the south of the gaseous disc contains cooler gas than the northern part, and the centre hosts warmer and less tenuous gas with a similar dense gas fraction compared to most galaxies of similar type. Our model results mostly agree with the empirical ones in the sense that the central region of NGC 5033 harbours warmer gas than that in the centres of normal spirals and lenticulars without showing AGN activity. Finally, the beam-averaged total molecular gas mass and gas surface density along the galaxy's major axis show a radial gradient, i.e. increasing from the outskirts up to the central region of size 1 kpc where there is a depression in both gas mass and surface density.