Star formation and infrared emission in galaxies

The relationship between star formation and infrared emission in galaxies will be investigated. If galaxies were simple objects and young stars were completely covered with dust, then all the absorbed light of the young stars would be reemitted in the infrared and from the infrared emission of galaxies we would infer the star formation rate (SFR) in them accurately. To show the complexities involved in real galaxies, we will use as a case study the late-type spiral galaxies. We will show that the heating of the dust is done mainly by the UV radiation of the young stars and therefore the infrared emission reveals the SFR in them. With a realistic model and its application to a number of galaxies, tight correlations are derived between SFR and total far infrared luminosity on one hand, and dust mass and 850 micron flux on the other. Other diagnostics of the SFR are examined and it is shown that there is consistency among them. Thus, the SFR for galaxies of all Hubble types has been determined as well as for interacting starburst galaxies. Combining different methods, the star-formation history of the universe has been determined and will be shown. Finally, some early results from the Spitzer Space Telescope will be presented.