Shock Compressions in the Interstellar Medium as triggers of Star Formation.

Infrared Dark Clouds (IRDCs) are the densest parts of Giant Molecular Clouds (GMCs) and the birth sites of massive stars and star clusters - indeed most of our Galaxy’s stars are expected to be born in such structures. However, the processes that lead to the formation of IRDCs and the ignition of their star formation are still unclear.

One possibility is triggering by collisions between GMCs leading to shock compression of parts of the clouds to high density and gravitational instability. Another possibility is shock compression of GMCs by supernova remnants or HII regions.

A third option is simply dissipation of turbulent and magnetic support in GMCs without the need for external influence.

To disentangle these possibilities, I propose to carry out an observational project to search for signatures of shocks, especially via SiO line emission, and disturbed kinematics, via CO line emission, in samples of GMCs and IRDCs.