The Final Step: Establishing the Relations Between Black-Hole Growth and Host-Galaxy Properties During the Last Half of Cosmic Time

One of the most important discoveries of the last two decades has been the realization that the lives of galaxies and their central super-massive black holes (SMBH) are inextricably intertwined, and in fact, have evolved together over cosmic time. In a real sense, a clearer understanding of the formation and evolution of one depends on that of the other. Observational studies at high redshift (z = 0.5 - 3) reveal compelling galaxy-SMBH coevolution despite relatively small sample sizes that almost certainly limit a full accounting of the factors influencing SMBH growth. The research team will take advantage of the wealth of existing data from deep and wide-field multi-wavelength galaxy surveys to conduct a thorough investigation of galaxy-SMBH coevolution over low-to-moderate redshifts (z = 0 - 0.8), an epoch covering roughly the final half of cosmic time, to connect SMBH-galaxy properties in the very distant universe with those we observe locally. The proposal will also support graduate research as well as middle/high-school teacher development workshops. The research team will exploit existing wide-field multi-wavelength (X-ray to far-infrared) surveys to identify approximately 7,100 galaxies with active galactic nuclei (AGN, i.e., actively accreting SMBHs), including nearly 200 dwarf galaxies, from a total of 300,000 galaxies spanning z = 0 – 0.8, which comprises a much larger sample than comparable studies. The UV-to-far-infrared data will yield galaxy redshifts, stellar masses (M*), star formation rates (SFRs), and structural parameters, while X-ray luminosities will be used to estimate the time-averaged SMBH accretion rate (), which minimizes the influence of intrinsic AGN variability. The collected data will be used to conduct statistically robust partial-correlation and multi-parameter studies to address multiple lines of inquiry, such as (e.g.) combining the IlustrisTNG simulation suite with the observed to predict the z = 0 SMBH mass vs. host galaxy M* relation and assess the relative importance of mergers and accretion on SMBH growth. Other questions to be considered include: do SMBHs and galaxy bulges continue to grow in lockstep over the last half of cosmic time? Do dwarf galaxies “grow” their black holes differently than more massive galaxies, and does the presence of an AGN somehow keep galaxies on the star-forming galaxy “main sequence”? This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.