Description
The inner regions of Milky Way (MW) are known to contain an enigmatic population of prominent molecular clouds characterised by extremely broad lines. The physical origin of these extended velocity features (EVFs) is debated, although a connection with the “dust lanes” of the Galactic bar has been hypothesised. In our work, we search for analogous features in the dust lanes of barred galaxies using PHANGS-ALMA CO(2-1) data, to confirm the existence of EVFs in other galaxies and to take advantage of the external perspective to gain insight into their origin. Within a sample barred galaxies, we find 34% containing one or more EVFs; unbarred galaxies lacked EVF signatures. Analysing the physical properties of EVFs, we find they possess large virial parameters, indicating they are strongly unbound regions. The most likely explanation for their origin is extreme cloud-cloud collisions with relative velocities in excess of 100km/s in highly non-circular flow driven by the bar. This interpretation is consistent with previous high-resolution observations in MW. Further evidence to our interpretation is shown from the high-sensitivity infrared observations from PHANGS-JWST Treasury Survey, revealing streams of gas that appear to be hitting the dust lanes at locations where EVFs are found. We argue that EVFs are the clearest examples of cloud-cloud collisions available in the literature, representing a unique opportunity to study cloud collisions and their impact on star formation.
