Institute for Advanced Study Informal Astrophysics Seminar

I describe my preliminary results in calculating the extragalactic backgrounds from star-forming galaxies at all energies. First, I construct very simple models of galaxies using relations like the Schmidt law. This lets me estimate quantities including the galactic size, gas mass, and metallicity using just the star-formation rate, star-formation mode (normal vs. starburst), and redshift as input. Then I can use a simple one-zone model of radiative transfer and Starburst99 synthesized spectra to calculate the ultraviolet to infrared spectra of galaxies. I also calculate the nonthermal emission, including radio and gamma rays, from these galaxies with one-zone models of cosmic ray populations. Finally, I put it all together and calculate the extragalactic background as well as the source counts at different wavelengths. I discuss the implications of these results. How much of the gamma-ray background do star-forming galaxies make up? (About half.) Are previous predictions for microJy radio source counts correct? (Yes.) And can star-forming galaxies make up the mysterious ARCADE GHz radio background? (No.)