Infrared galaxies are galaxies that emit a significant amount of their energy at infrared wavelengths, rather than visible light. This can be due to a variety of factors, such as the presence of dust that absorbs and re-radiates starlight at longer wavelengths, or the intense star formation or active galactic nuclei within the galaxy that produce copious amounts of infrared radiation. Studying infrared galaxies can provide insights into the processes of star formation, galaxy evolution, and the formation of dust in the universe. Researchers use infrared telescopes and instruments to study these galaxies and understand their properties and contributions to the overall energy output of the universe.