Molecular Gas Morphologies in Nearby Main Sequence Galaxies

Presentation held at the "Galactic bars: driving and decoding galaxy evolution" conference 2023.

The morphology of a galaxy results from secular and environmental processes during its evolutionary history. As such, it is an important tracer of galaxy evolution. We present the first visual classification of morphologies based solely on the molecular gas distribution for a large sample of 79 nearby main-sequence galaxies, using 1" resolution CO(2-1) ALMA observations taken as part of the PHANGS survey. We devise a morphology classification scheme for different types of bars, spiral arms (grand-design, flocculent, multi-arm and smooth), rings (central and non-central rings) similar to the well-established optical ones, and further introduce classes to describe the shape of bar lanes. Not only do we find a generally good agreement between our cold gas based morphologies and the ones based on stellar light, but also find that both our bars as well as grand-design spiral arms are preferentially found at the higher mass end of our sample. We find that more curved bar lanes show a shorter radial extend in molecular gas, have  lower molecular to stellar mass ratios than those with straighter geometries.