Presentation #232.02D in the session “ Star Formation in Galaxies”.
I will present a new and dust-unbiased measurement of the cosmic evolution of star formation well-beyond “cosmic noon” using only radio continuum data. The radio luminosity of a star-forming galaxy is proportional to its star formation rate through the remarkably tight FIR/radio correlation. Unfortunately, most star-forming galaxies are extremely weak radio sources and it’s necessary to measure their source count below 1 microJy at 1.4 GHz to constrain their evolution; e.g. the Milky Way would be 1 microJy at z = 2.2 with 10X luminosity evolution and at z = 0.8 with no evolution. At microJy flux levels, the sources are dominated by star-forming galaxies over AGN by a factor of 10, unlike at higher flux densities. Using the MeerKAT 64-element array, we have recently made the deepest ~1.4 GHz radio image (rms ~550 nJy), sensitive to Milky-Way equivalents beyond “cosmic noon.” We used the P(D) distribution from the confusion-limited image to count sources down to 0.25 microJy for the first time. These source counts are the product of the evolution of the local luminosity function over all redshift assuming a star formation rate density evolutionary function, and can therefore constrain the star formation history of the universe. We have found that star-forming galaxies must have evolved ~50% more strongly than predicted by Madau and Dickinson (2014) from FUV and IR data.