Not dead yet: Low-level star formation and active galactic nuclei in the continued evolution of early-type galaxies in the nearby universe

One of the most pressing issues in current models of galaxy formation and evolution is the role of accreting supermassive black holes (SMBHs) in shaping the characteristics of their host galaxies, and a number of lines of evidence suggest that their evolutions are intricately linked. This symbiotic relationship may be at the root of the observed scaling relations between SMBH and host galaxy properties, active galactic nucleus (AGN)-driven outflows, and the suppression of star formation (SF). Although the bulk of rapid SMBH growth, SF, and galaxy evolution is believed to have been carried-out at higher redshifts (e.g., z > 2), studies of the less extreme versions of these processes in low-redshift, nearby galaxies can provide important insights into the underlying physics of the mechanisms responsible for shaping galaxy evolution.;Here, I present the results of a series of interferometric radio studies of SMBH growth, energetic AGN feedback, and SF in a large sample of nearby early-type galaxies (ETGs). The key results are as follows: 1) Sensitive, high-resolution VLA continuum observations have revealed that about 42% of nearby ETGs harbor compact, nuclear radio continuum sources, an indication that the SMBHs in these galaxies are continuing to accrete material at low levels. The presence and properties of these compact radio sources appears to depend on host galaxy characteristics such as black hole mass and dust features, which suggests a link between different ETG evolutionary paths and current nuclear activity. 2) In some cases, such as the intermediate-mass black hole candidate in the nucleus of NGC404, the roughly 450,000 solar-mass black hole is accreting at such a low rate and producing so little mechanical energy that AGN feedback is not a significant factor in this galaxy's evolution in the foreseeable future. 3) At least one nearby ETG, NGC1266, presents a strong case for an AGN feedback-driven molecular gas outflow. This suggests that even low-luminosity AGNs in nearby ETGs can drive massive outflows capable of disrupting the raw materials needed for future SF. 4) CO-rich ETGs commonly have kpc-scale disks of radio emission similar to those found in spirals. However, at low molecular gas masses, ETGs have weaker radio emission than expected from the extrapolation of SF scaling relations derived from samples of spiral galaxies. Possible explanations include a combination of decreased SF efficiency, weak magnetic fields, and a higher incidence of environmental effects compared to spirals. 5) Direct evidence for a strong impact on SF due to AGN feedback in nearby ETGs is lacking. However, weak AGNs appear to commonly co-exist with SF in gas-rich ETGs, supporting the existence of a galaxy-SMBH co-evolution in the past, and perhaps even again in the future if larger supplies of gas become available.