The majority of the stellar mass in the Universe lies in galactic spheroids, which also host supermassive black holes (SMBH). The origin of these key structures can be clarified through the interplay of new multi-wavelength survey observations and improved theory, essential for guiding and interpreting the observations. This research focuses on the growth of cosmic structure and on the two opposing effects of early, efficient star formation, and the quenching of this process in massive dark-matter halos, which together govern the formation of blue and red galaxies. This project should discriminate between galaxy spheroid buildup by cold gas inflows and disk instabilities and the alternative of major and minor mergers. The work should also identify the roles of nuclear activity versus virial shock heating in halos above a threshold mass, distinguish satellite from central quenching, and understand the cross-talk between the shutdown of star formation and the development of spheroidal stellar components and SMBHs. Detailed models of early-type galaxy formation will be compared with observations of mergers and other processes out to high redshifts, and also of nearby galaxies whose properties can be studied in detail. The work is supported by a large program of recently completed and planned follow-on computer simulations, using the most up-to-date cosmological parameters and having high mass and spatial resolution. Additional high-resolution hydrodynamic simulations will clarify galaxy formation processes and permit the calculation of kinematics, spectra and images, including dust scattering and absorption. It is crucial that simulations are 'observed' in ways that accurately mimic observations of real galaxies.
The team will involve students from underrepresented groups in astrophysical theory research, including the ability to understand the implications of the latest observations. This work pushes the computational envelope, and all codes and outputs will be available to the astrophysical community. Planned computer visualizations will help to understand the simulations while simultaneously making the results accessible to other researchers and to the public.
The main goals of this research project were all fulfilled: • Running and analyzing the highest resolution accurate simulations of the large scale structure of the universe. These are the Bolshoi simulations, based on the cosmological parameters from NASA's WMAP team and the European Space Agency's Planck team. For more information, images and videos, and links to popular articles, see our website: http://hipacc.ucsc.edu/Bolshoi . • We developed improved models of the evolving galaxy population that are able to predict the sizes and internal velocities of galaxies. These predictions agree with observations both nearby and in the early universe. • We have run 100 high-resolution simulations of galaxies, and used our Sunrise code to make realistic images of these simulated galaxies. When we compare them with images from CANDELS, the largest-ever Hubble Space Telescope survey, we found improving agreement as we improved our simulations — especially after we included the effects of radiation pressure from massive young stars. In particular, our simulations appear to explain the presence of massive clumps of gas and forming stars in early galaxies as due to disk instabilities, which also lead to galaxy shrinkage as these clumps and additional gas are funneled into the galaxy centers. Our simulations also predicted that the lower mass galaxies will appear very elongated, as observed by CANDELS. • In addition, PI Primack with UCSC colleague Piero Madau have organized an international collaboration, Assembling Galaxies of Resolved Anatomy (AGORA), to critically compare highresolution galaxy simulations with each other and with observations. AGORA's "flagship" paper, containing details of the shared astrophysics and initial conditions, was published earlier in 2014. AGORA has 110 members, including most of the leaders and active participants in high-resolution galaxy simulations worldwide. • Graduate students who were funded by this grant and who have now received their PhD degrees include Lauren Porter (a Black woman) and Christopher Moody (a Hispanic man), thus increasing the diversity of the astrophysics community.
