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Date and Time of the Query: 2019-04-20 T01:48:04 PDT
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For refcode 2015A&A...578A..70K:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
2015A&A...578A..70K Mapping CS in starburst galaxies: Disentangling and characterising dense gas Kelly, G.; Viti, S.; Bayet, E.; Aladro, R.; Yates, J. Abstract. Aims: 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. Methods: 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 NGC 3079 and NGC 6946. We also detected formaldehyde (H_2_CO) and methanol (CH_3_OH) in both galaxies. We marginally detect the isotopologue C^34^S. Results: We calculate column densities under LTE conditions for CS and CH_3_OH. 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. Conclusions: Using the rotational diagram method for CH_3_OH, we obtain a lower limit temperature of 14 K. 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 CH_3_OH). We also estimate the quantity of the dense gas. We find that, provided there are between 10^5^ and 10^6^ dense cores in our beam, for both target galaxies, emission of CS from warm (T = 100-400 K), dense (n(H_2_) = 10^5-6^ cm^-3^) cores, possibly with a high cosmic ray ionisation rate (zeta = 100zeta_0_) best describes conditions for our central pointing. In NGC 6946, conditions are generally cooler and/or less dense further from the centre, whereas in NGC 3079, 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. Key words: galaxies: starburst, galaxies: star formation
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