Shocks are a ubiquitous phenomenon in the interstellar medium (ISM) of galaxies. They may be driven by supernova explosions, the pressure of photoionized gas, stellar winds, and collisions between fast-moving clumps of interstellar gas, where the fluiddynamical disturbances proceed at a velocity that exceeds the local sound speed because of the presence of large pressure gradients. The processes of birth, evolution, and death of stars are always associated with shocks. 

Towards a further understanding of shocks in regions of star formation, XAO astronomers Yuxin He, Jianjun Zhou, Jarken Esimbek, and MPIA astronomer Christian Henkel and their colleagues have performed a systematic study of 43 southern star-forming regions in HNCO 4₀₄–3₀₃, SiO 2–1, and HC₃N 10–9, which are good tracers of shocks, based on the MALT90 survey, the 870 μm ATLASGAL survey, and Herschel 160, 250, 350, and 500 μm data. These sources were divided into three groups: those in the Central Molecular Zone (CMZ), those associated with bubbles (Bubble), and the remaining sources, which are termed “normal star-forming regions” (NMSFR). We find that the dust temperature T_d, and the abundance ratios N_HNCO/N_SiO and N_HNCO/N_HC3N show a decreasing trend toward the central dense regions of CMZ sources, while N_HC3N/N_SiO moves in the opposite direction. Moreover, a better agreement is found between T_d and N_HC3N/N_SiO in Bubble and NMSFR category sources. Both outflow and inflow activities have been found in eight of the 16 bubble and NMSFR sources. The low outflow detection rate indicates either that in these sources the SiO 2–1 line wing emission is below our sensitivity limit or that the bulk of the SiO emission may be produced by the expansion of an H II region or supernova remnant, which has pushed molecular gas away, forming a shock and yielding SiO. The results have been published in The Astrophysical Journal Supplement (He et al. 2021, ApJS, 253, 2).