Local Ultraluminous Infrared Galaxies


The most intense starburst galaxies are often very dusty; the dust absorbs the ultraviolet light from the young stars and heats up, reradiating that energy in the infrared. So they are order of magnitude brighter in the far infrared (unobservable from the ground) than they are in the optical.



What do they look like? Often mergers of massive, gas-rich galaxies, with star formation rates > 100 Msun/yr:


(from Hibbard & Yun 1997)

If galaxy collisions and mergers are common at high redshift, as structure forms, these "LIRGs" may be the local analogues to high redshift starburst galaxies. They would not be detected as Lyman break galaxies, because they are so dusty the ultraviolet is blocked by the dust. We need to look in the redshifted far-infrared where they are brightest, ie in sub-millimeter wavelengths. This is observable from the ground!