Quasars Probing Quasars

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In the fifty years since the discovery of quasars, a picture of these enigmatic objects has emerged wherein quasars are supermassive black holes residing at the centers of large galaxies. The black hole may have a mass of millions to billions times that of the sun. As this picture implies, the quasar phenomenon is one and the same as that of the objects referred to as "active galactic nuclei." All are characterized by enormous luminosity such that the quasar frequently outshines the light from all of the billions of stars in its host galaxy. Their extreme luminosity makes it possible to observe quasars located at billions of light-years from earth. Due to the finite speed of light, this means that astronomers can literally observe quasars at an earlier epoch in the universe, the age of the formation of galaxies. This project will specifically study pairs of quasars. Quasar pairs are relatively rare and are not physically associated with one another. Instead, they are a superposition of two quasars at different distances that appear close together on the sky. As the light from the more distant quasar passes by the nearer one, any gas in the halo of the galaxy hosting the latter quasar, the so-called "circumgalactic medium," imprints a signature on the spectrum of the more distant quasar, allowing the study of the characteristics of that gas and giving clues as to the mechanism of the formation of the host galaxy. This team of researchers has assembled a sample of such pairs and will use them to study the circumgalactic gas as well as the gas between galaxies. The project will also support internship programs at a minority-serving college and public outreach.This project is an extension of the well-established Quasars Probing Quasars project into several new scientific directions and support astronomical outreach into the Hispanic community of Salinas Valley. Specific scientific emphasis will be concentrated on the circumgalactic medium of massive galaxies, AGN physics, and the intergalactic medium at redshift of about 2. The project will utilize data from essentially every large-aperture, optical/near-IR telescope and will leverage state-of-the-art cosmological simulations to interpret results and test theories of galaxy formation, quasar feedback, cosmic re-ionization, and supermassive black hole evolution. The core of the project will be the use of pairs of quasars to probe the intergalactic and circumgalactic media at high redshift as well as to provide evidence for the resolution of fundamental questions in quasar physics. Typical quasar pairs are not physically associated with one another but the light from the background quasar is imprinted by material associated from the nearer, lower redshift member of the pair. This allows determination of the size of structure in any absorbing gas along with its density, mass, etc. Three distinct but coupled programs will be supported: (1) to test theories of galaxy formation by elucidating the properties of the circumgalactic medium around galaxies hosting quasars and sub-millimeter galaxies; (2) to estimate timescales for the active galaxy phenomenon using the transverse proximity effect; and (3) make the first measurements of the small scale structure of the intergalactic medium at redshifts around 2. This is an ambitious program for which the PI and his collaborators have the necessary physical resources (telescope time, etc.) and intellectual prowess.