V. Charmandaris on the IR properties of Galaxies
Starbursts, that is episodal strong star formation, happens in regions wiith a lot of dust. It plays an important role in the whole process of star formation, but one of its properties is: it blocks light.
Well, optical light is obscured but by observing infrared wavelengths, one can look through the dust. The speaker reminds us of the beautiful studies in the Antennae galaxy, where the regions that are dark and invisible in an optical image are the brightes in the infrared.
IR-luminosity is nowadays quite well calibrated as an absolute measure of the star-formation-rate (SFR) and has become more popular (than for example the H-alpha-flux) since the upcome of many IR-instruments during the last decade. In the mid- and far-infrared, the dust istself stars to glow due to (almost) black-body emission and measuring the amount and the temperature of the dust in these wavelengths also contributes to the understanding of what is going on. As usual, it is all information together that gives the most complete picture.
(U)LIRGS are (ultra-)luminous-infrared-galaxies and you can guess why they are called this way. Arp220 is the most close-by of these rare objects and it is very well studied. ULIRGS are most likely to be a short phase during a merger event of two large galaxies when a lot of stars are formed.