The submillimeter wavelength range is a critical window to understand how the galaxy ecosystem works. The largest submillimeter observing facility, ALMA, has great sensitivity for compact, small-scale structures in galaxies, but is insensitive to diffuse, large-scale features that could play a significant role in the baryon cycle of galaxies. Additionally, it lacks the mapping efficiency to probe the variety of thousands of nearby galaxies.
AtLAST, a 50-m submillimeter telescope project, is a necessity for the next major breakthroughs. Here I will present how AtLAST can uniquely solve questions regarding the large-scale ISM in the Magellanic Clouds, magnetic fields in 102 nearby galaxies, chemical and physical evolution of 104-105 giant molecular clouds and star-forming regions each with tens of spectral lines, and cold gas reservoir and baryon cycling in 104-105 galaxies in the local Universe.
