UCL Astrophysics Group


Starburst Galaxies

Figure 1: The Fireworks Galaxy (NGC 6946), located 20 million light-years away. Dense gas (CS) emission is observed in the central region of the galaxy. Despite changing offset positions by just 10 – 20 arcseconds from the central position, clear detections are not made in all locations.

Observations were taken of the CS(J = 2-1) and CS(J = 3-2) lines in several locations around the centre of both galaxies (e.g. see figure 1) using the IRAM-30m telescope. Estimations of the gas properties are made under LTE assumptions using the rotational diagram technique (Goldsmith & Langer 1999). These are refined using the RADEX code (Van der Tak et al. 2007) run over a wide range of temperatures and column densities to gain a set of best-fit parameters for each line.

In addition to this, the formation of CS was modelled using UCLCHEM. A variety of parameters determine the environment in which this formation occurs. By varying these and feeding the output into the molecular line radiative transfer code, SMMOL, model line profiles were produced. Comparisons between these and the observed line profiles can be made in order to determine the likely physical conditions in which CS forms.