Abstract: Luminous and Ultra-luminous Infrared Galaxies (U/LIRGs) are the most extreme star-forming galaxies in the local Universe, and they are primarily triggered by interacting and mergers of gas-rich galaxies. As such, they provide excellent local laboratories to study in detail the physical processes that could be associated with the hierarchical transformation of star-forming galaxies into elliptical galaxies. However, the dusty nature of U/LIRGs poses great challenges in accurately characterizing their properties at UV/optical wavelengths. In this talk, I will introduce a recently completed multi-band survey of a representative sample of 68 local U/LIRGs conducted with the Karl G. Jansky Very Large Array (VLA), which provides a relatively extinction-free view of the energetics in these extreme local systems. Using arcsecond-resolution observations for the survey, we find tight correlations between the 3 – 33 GHz radio continuum and mid- and far-IR emission on kpc scales, with no clear distinction between AGN and star forming activity. However, compared to star-forming activity, AGN tend to show steeper spectral slopes towards higher radio frequencies. High-resolution continuum observations at 15 and 33 GHz reveal diverse nuclear morphologies in these systems within the central kpc, with which we identify and characterize over 100 compact regions of radio continuum emission at ~100pc scales that are associated with star formation and/or AGN activity. We identify a sample of radio-bright galactic nuclei that are forming stars near the maximal capacity as predicted by theoretical models for star-forming disks supported by dust-reprocessed radiation pressure. Several of these nuclei have been identified to host AGN, and the rest may be going through a key phase of heavily obscured co-evolution between supermassive black holes and circumnuclear star formation. I will briefly discuss ongoing and future multi-wavelength efforts to further investigate the nature of these compact nuclei.
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