Large–scale molecular shocks in starburst and active galaxies

¹ Centre for Astrophysics Research, University of Hertfordshire, UK; e-mail: a.usero@herts.ac.uk
² Observatorio Astron´omico Nacional, Spain; e-mail: s.gburillo@oan.es; a.fuente@oan.es
³ DAMIR, IEM-CSIC, Spain; e-mail: martin@damir.iem.csic.es
⁴ Institute de Radio-Astronomie Millim´etrique, France; e-mail: neri@iram.fr

Abstract

Large-scale shocks propagate in the interstellar medium of starburst and active galaxies, driven by the same mechanisms that regulate the evolution of the star formation and AGN episodes. The imprints of shocks in the chemical composition of the molecular gas provide useful means to identify those mechanisms and to asses their effects. We review some recent and on-going studies of the molecular gas chemistry in the nearby star-forming galaxies IC 342, NGC 253 and M 82, based on the well known shock tracer silicon monoxide (SiO). When mapped at high–spatial resolution the SiO emission reveals substantial differences among these galaxies. In particular, the location of shocks and their dominant driver are in correspondence with the evolutionary stage of the starburst episode. Complementary observations of other tracers of shock chemistry, like methanol (CH₃OH), help us to improve the characterization of the shock mechanisms. We also present the first high-resolution observations of the SiO emission in the Seyfert 2 galaxy NGC 1068.