This research will use the superb photometric and spectroscopic data from the Sloan Digital Sky Survey to study the clustering of Active Galactic Nuclei at intermediate and high redshifts. The clustering of such highly biased populations measures the typical mass of their host dark matter halos. This will result in the first definitive measurement of the large-scale clustering of quasars at redshifts beyond three, as a function of their luminosity and black hole mass. A survey of close quasar pairs at high redshift should determine whether these objects form in rare, high-density peaks, while targeted deep imaging will test for the frequency of such rare peaks, as well as for the existence of the predicted host clusters of galaxies. In addition, this study will make the first determination of the fraction of obscured quasars at high luminosities, and determine whether the census of high luminosity objects is close to complete.
The research supports a full-time graduate student, continuing a strong record of undergraduate and graduate training. As part of a long-running quantitative introductory course in astrophysics, the principal investigator for this project has been distributing essays describing recent exciting developments in the field. This will continue, describing from an insider's perspective how science is done, and how astronomers use data and quantitative reasoning to reach their conclusions. These essays will become more widely available through a web site under development, taking advantage of the natural excitement and curiosity that the public feels for this fast-moving field.
One of the great discoveries of the last two decades is the fact that every large galaxy hosts a black hole in its center. These black holes are massive, ranging from a few million times the mass of the Sun to several billion times more massive than the Sun. These black holes have grown to this enormous size by the infall of gas and stars into them, and presumably also by the mergers of black holes as galaxies crash into each other. It has now become clear that the process of black hole growth is intimately tied to the growth of galaxies themselves. In this proposal, my colleagues and I used data from the Sloan Digital Sky Survey and other telescopes to explore aspects of this question in detail. We used the fact that the growth of black holes is something that we can observe directly. While a black hole has such a strong gravity that nothing can escape from it, not even light, material falling into the black hole, before it disappears forever over the event horizon, will heat up tremendously and glow incredibly brightly, in a phenomenon we call a quasar. Thus paradoxically, black holes can be seen as some of the most luminous objects in the universe. We studied quasars in a wide variety of contexts. We found some of the best examples known of *double* quasars, in which merging galaxies, each with its own black hole, trigger the infall of gas into the central regions. We explored populations of previously unrecognized quasars whose fireworks are hidden by an obscuring sheen of dust. We studied the properties of the most distant quasars known, whose light left them when the Universe was less than a billion years old. We studied populations of gravitationally lensed quasars, in which the distortion of space by the gravitational effects of a foreground galaxy makes the quasar appear double. And we explored the properties of the black holes themselves, asking how their population has evolved with time. This work has given us new insights into the physical nature of quasars and their relation to the galaxies in which they live. It is becoming increasingly clear that the galaxies and their central black holes evolve together, and directly affect one another, in ways that are starting to become clearer.
