Starburst Galaxies

NGC6946 gas emission

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” from the central position, clear detections are not made in all locations.

Starburst galaxies have a rapid rate of star formation. These are likely temporary states, as star formation would use all available gas in a relatively short amount of time. The two nearby galaxies, NGC 3079 and NGC 6496 (Figure 1), show evidence of bubbles of starbursts around their centres. The diatomic molecule CS has been shown to be a good tracer of the dense gas (n(H2) > 10^5 cm-3) that is necessary for star formation in harsh conditions.

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 UCL CHEM. 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.

Page last modified on 17 aug 15 10:49 by Kajal H Nakum