SIMBAD references

We observe the dense gas tracer CS in two nearby starburst galaxies to determine how the conditions of the dense gas varies across the circumnuclear regions in starburst galaxies.Using the IRAM-30m telescope, we mapped the distribution of the CS(2-1) and CS(3-2) lines in the circumnuclear regions of the nearby starburst galaxies NGC3079 and NGC6946. We also detected formaldehyde (H₂CO) and methanol (CH₃OH) in both galaxies. We marginally detect the isotopologue C³⁴S. We calculate column densities under LTE conditions for CS and CH₃OH. Using the detections accumulated here to guide our inputs, we link a time and depth dependent chemical model with a molecular line radiative transfer model; we reproduce the observations, showing how conditions where CS is present are likely to vary away from the galactic centres.Using the rotational diagram method for CH₃OH, we obtain a lower limit temperature of 14K. In addition to this, by comparing the chemical and radiative transfer models to observations, we determine the properties of the dense gas as traced by CS (and CH₃OH). We also estimate the quantity of the dense gas. We find that, provided there are between 10^5and 10^6dense cores in our beam, for both target galaxies, emission of CS from warm (T=100-400K), dense (n(H₂)=10^5–6cm^–3) cores, possibly with a high cosmic ray ionisation rate (ζ=100ζ₀) best describes conditions for our central pointing. In NGC6946, conditions are generally cooler and/or less dense further from the centre, whereas in NGC3079, conditions are more uniform. The inclusion of shocks allows for more efficient CS formation, which means that gas that is less dense by an order of magnitude is required to replicate observations in some cases.