The "shocking" interaction between supernova remnants and molecular clouds

Despite the importance of massive stars and star clusters for the energy content, stellar population and evolution of galaxies, the mechanism that ignites their formation in molecular clouds is still poorly addressed. Infrared Dark Clouds (IRDCs) are the likely precursors of massive stars. It has been suggested that IRDC formation and dynamical processing by multiple shock episodes triggered by bubbles, such as HII regions and Supernova Remnants (SNRs), can efficiently initiate star formation within these clouds. It is thus important to understand the conditions of density and temperature set by large-scale shocks in IRDCs to constrain the ignition of star formation in these objects. In this work, I will present the large scale shock triggered by the SNR W44 in the IRDC G034. I will show how the shock, probed by Silicon Monoxide (SiO) and observed with ALMA, enhances the density of the processed gas to values compatible with those required for massive star formation and has helped to shape the cloud. Thanks to the high resolution achieved by ALMA, the internal physical structure of the shock was resolved for the first time, providing a direct test to Magneto-Hydro-Dynamic (MHD) shock theories. Moved by these results, we have initiated the large single-dish observing program SHREC, aimed to observe SiO(2-1) emission in SNRs interacting with molecular clouds. During the talk, I will briefly introduce the aim and technical aspects of SHREC and present preliminary results obtained toward the SNRs IC443 and W41