Letter to the Editor

Mechanical feedback in the molecular ISM of luminous IR galaxies

¹ Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands e-mail: loenen@astro.rug.nl
² ASTRON, PO Box 2, 7990 AA Dwingeloo, The Netherlands
³ Astronomy Department, University of California, Berkeley, CA 94720, USA

Received: 4 June 2008
Accepted: 4 July 2008

Abstract

Aims. Molecular emission lines originating in the nuclei of luminous infra-red galaxies are used to determine the physical properties of the nuclear ISM in these systems.

Methods. A large observational database of molecular emission lines is compared with model predictions that include heating by UV and X-ray radiation, mechanical heating, and the effects of cosmic rays.

Results. The observed line ratios and model predictions imply a separation of the observed systems into three groups: XDRs, UV-dominated high-density ( cm^-3) PDRs, and lower-density ( cm^-3) PDRs that are dominated by mechanical feedback.

Conclusions. The division of the two types of PDRs follows naturally from the evolution of the star formation cycle of these sources, which evolves from deeply embedded young stars, resulting in high-density ( cm^-3) PDRs, to a stage where the gas density has decreased ( cm^-3) and mechanical feedback from supernova shocks dominates the heating budget.