EPoS Contribution
EPoS Contribution
Extended warm and dense gas towards W49A: starburst conditions in our Galaxy?

Zsofia Nagy
Kapteyn Astronomical Institute & SRON, Groningen, Netherlands
The star formation rates in starburst galaxies are orders of magnitude higher than in local star-forming regions, and the origin of this difference is not well understood. We use sub-mm spectral line maps to characterize the physical conditions of the molecular gas in the luminous Galactic star-forming region W49A and compare them with the conditions in starburst galaxies. We probe the temperature and density structure of W49A using H2CO and HCN line ratios over a 2x2 arcminutes (6.6x6.6 pc) field with an angular resolution of 15'' (~0.8 pc) provided by the JCMT Spectral Legacy Survey. Comparing the observed line intensity ratios with non-LTE radiative transfer models, our results reveal an extended region (about 1x1 arcminutes, equivalent to ~3x3 pc at the distance of W49A) of warm (>100 K) and dense (>10^5 cm^-3) molecular gas, with a mass of 2x10^4-2x10^5 M_Sun. These temperatures and densities in W49A are comparable to those found in clouds near the center of the Milky Way and in starburst galaxies. The highly excited gas is likely to be heated via shocks from the stellar winds of embedded, O-type stars or alternatively due to UV irradiation, or possibly a combination of these two processes. Cosmic rays and X-ray irradiation are less likely to be the source of the heating in the case of W49A.
Floris van der Tak, SRON, Netherlands
Gary Fuller, Jodrell Bank Centre for Astrophysics, University of Manchester, UK
Marco Spaans, Kapteyn Astronomical Institute, Netherlands
Rene Plume, University of Calgary, Canada