How galaxies and the stars within them evolve is one of the most important questions concerning the production of most of the electromagnetic energy and chemical evolution in the universe. Determining the cosmic evolution of star formation and the star formation rate density (SFRD) has historically been a multiwavelength effort, with ultraviolet and infrared approaches claiming most of the popularity. While these methods have their merits, UV and NIR wavelengths are hindered by the effects of dust attenuation. Radio observations are advantageous in this pursuit because they are unaffected by the presence of dust while maintaining the ability to make high-resolution images.
Local Universe
Measures of the evolution of the star formation rate density (SFRD) are only as good as the value calculated for today’s universe. The local radio luminosity function calibrates the models and measurements of the evolution of star formation over cosmic time, but more importantly provides a baseline with which to compare the evolution seen at higher redshifts. The current generation of redshift surveys provide distance information for thousands of galaxies over a large angular area of sky - giving better statistics and averaging over as much cosmic variance as possible.
Cosmic Noon
Faint radio sources are able to constrain the evolution of the cosmic SFRD through both direct and statistical source counts together with the tight FIR-radio correlation. Our ability to “directly” measure source counts is made difficult by the expense of making simultaneously sensitive and high-resolution images with interferometers. Rather than avoiding confusion-limited images, it is possible to capitalize on the statistics involved to probe unprecedented sensitivity levels (< 0.5 microJy) and yield the source counts and flux density distribution of a never-before-seen faint microJy population.