This research program will use the multiwavelength data on the COSMOS field to select Active Galactic Nuclei (AGNs) with a wide range of optical and IR properties. Multi-object spectroscopy with Magellan/IMACS will be used to spectroscopically confirm ~3000 AGNs, reaching the classical Seyfert/quasar boundary at a redshift of 3 and including about 300 quasars with redshift > 3. The deep multiwavelength observations will allow studies of the total AGN energy density in the universe, including a bolometric luminosity function for obscured AGN to redshift ~1 and Type 1 AGN to redshfit ~4. Time domain data will be used to measure reverberation between the continuum and the lines.
Over 13.7 billion years, the universe has evolved from a hot undifferentiated soup of radiation and fundamental particles into a cold place sparsely filled with galaxies sculpted by the action of gravity. It has become clear over the past decade that black holes are ubiquitous in the center of galaxies and the black hole mass is proportional to the mass of old stars in the host galaxies. Black holes grow and are fueled from the same drizzle of in-falling gas and wholesale mergers that make galaxies grow. The story of galaxies and black holes are parallel story lines of cosmic history. In fact, the connection is even more intimate. When galaxies become active, or switch on as compact sources of non-thermal radiation called quasars, gas can be driven out and star formation can be quenched. Supermassive black holes interfere with the stellar buildup from small to large galaxies. Early in the universe, mergers rapidly created massive galaxies and massive black holes within them, and their active phases correspond to highly luminous quasars. Galaxies like the Milky Way grow by mergers and steady in-fall of gas from intergalactic space. The build-up of stars in a middleweight galaxy is extended until recent cosmic times by outflows from a sporadically active black hole. This project was designed to paint a picture of the interrelationship between galaxies and the supermassive black holes they contain, and understand the ways in which back holes can be active or inactive. The survey used for this purpose was the Cosmic Evolution Survey (COSMOS), the largest contiguous region of sky surveyed by the Hubble Space Telescope and a part of the sky where an unprecedented array of multi-wavelength imaging data has been assembled. In this project, spectroscopy was obtained of X-ray sources to identify active supermassive black holes ten to twenty times less massive than have been found in other surveys, and black holes that are starved of fuel and in a feeble state of activity. Over 500 such active galaxies were identified, allowing their fuelling and growth over cosmic time to be studied statistically. The resulting evolutionary picture is this. The present day universe is large, cold, and relatively quiet. Galaxies are so far apart that they rarely meet or merge, and there’s not much supply of fresh gas for star formation to occur in intergalactic space. Disks are kept at a moderate level of star formation by ingesting the occasional dwarf galaxy. Over the past few billion years, black holes have grown in proportion with their parent galaxies, but their glory days are behind them. Most are starved of fuel and show feeble nuclear activity. The most massive black holes can enter a quasar phase, but only for a small fraction of the time. In a snapshot view most galaxies appear to be quiescent. This is the universe in its dull and plodding old age. Rewind to the universe when it was half its present age. The COSMOS survey was used to find many active galaxies from this epoch. Light emitted from galaxies then has a redshift of 0.8, so the universe was half its current size and twice as hot. Things are pretty lively; there’s lots of gas available to fuel star formation and nuclear activity, so both are at twenty times their present day levels. The most massive galaxies and black holes are fully formed but middleweight objects are being actively assembled and fueled. This is the universe in its prime. Now go back further to the universe when it was a quarter of its age, the situation of the opening vignette. The redshift is 2, so the universe is a third its current size and three times as hot. This corresponds to the limit of the COSMOS survey for identifying feeble active galaxies. Acquisitions, mergers, and hostile takeovers are in full swing. Most galaxies are not mature or fully formed but they are in the white heat of their growth phase, Fuel for nuclear activity is abundant. The star formation and nuclear activity levels are a few thousand times their levels today. This is the universe as a wild adolescent. Before this time, information is fragmentary. Supermassive black holes are growing rapidly but they are shrouded in thick dust and difficult to detect in any optical or X-ray survey. Large telescopes on the ground and the Hubble Space Telescope work at their limits to go back any further in time. At the limits of observation a newly minted galaxy is a few hundred times dimmer than a similar nearby galaxy, and the bulk of the stellar energy has been stretched to infrared wavelengths, leaving an optical telescope grasping at straws of light. The complex interplay between galaxy evolution and black hole growth and fueling will remain a topic of great interest in observational cosmology.
