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Galactic and Extragalactic Astronomy

With modern facilities working at a large range of wavelengths (including telescopes at Apache Point Observatory , Subaru, and Atacama), and data gathered in large surveys combined with state-of-the-art advances in theory and modeling, we are starting to put together a comprehensive picture of the formation, evolution, and present-day characteristics of galaxies.

Much of the department's observational work on this problem has been carried out in the context of surveys. We have played a leadership role in the Sloan Digital Sky Survey (, and have used the data to explore and characterize the properties and environments of galaxies in the present-day universe (Gunn, Strauss) from their photometric and spectroscopic properties as well as weak lensing to learn about their masses. Clusters of galaxies are both fascinating astrophysical laboratories in their own right and powerful probes of cosmology (Bahcall, Gunn, Strauss). We are also very interested in the evolution of Active Galactic Nuclei and quasars (Strauss, Gunn, Tremaine) and their relationship with "ordinary" galaxies and the demographics of black holes. We have discovered some of the most distant quasars in the universe, studied their demographics over cosmic time, and explored the nature of obscured quasars. We are carrying out a variety of studies of distant galaxies using quasar absorption lines (Jenkins, Bowen), very deep imaging and spectroscopy, and strong gravitational lenses (Strauss).

Computational hydrodynamic and magnetohydrodynamic simulations of disk galaxies with sub-parsec resolution (E. Ostriker) are used to study the interstellar medium and star formation, as well as the origins of spiral-arm substructure and non-circular gas motions in galaxies. Observed star formation rates depend on both the gas and stellar contents of galaxies, with orders of magnitude increase in the specific rate going from dwarfs to starbursts.  Recent numerical and analytic work has focused on explaining how these dependencies come about, and the ways in which feedback from massive stars may enable star formation to self-regulate.

We are participating in a number of on-going and planned surveys. SDSS is now entering its third phase of operations (, which will include spectroscopy of 1.5 million more galaxies and 150,000 more quasars, both as cosmological probes and to study their properties and evolution. We have entered a collaboration with the National Astronomical Observatory of Japan to develop and use a new wide-field camera (Hyper-SuprimeCam) on the 8.2-m Subaru Telescope in Hawaii ( to carry out wide-field surveys of the distant universe to study (among other things) galaxy evolution (Gunn, Strauss, Knapp, Spergel); this instrument should see first light in 2011. The Large Synoptic Survey Telescope (LSST, will be a dedicated telescope with a 3.5-degree field of view and an affective aperture of 6.7 meters; the 20,000 square degree survey of the sky to r=27 will revolutionize our understanding of galaxies both near and far (Lupton, Strauss). Finally, we (Spergel, Kasdin, Vanderbei) are developing plans for the "Telescope for Habitable Earths and Interstellar /Intergalactic Astronomy'' (THEIA), a 4-meter successor to the Hubble Space Telescope, which will (among other things) allow us to carry out extremely deep surveys of the very distant universe.

Studies of our own Galaxy and its immediate environs have also been enabled by this survey. We have a long-standing interest in the dynamics, dark matter and stellar content, and mass of the Milky Way (Knapp, Tremaine, Gunn, Ostriker), and the SEGUE and APOGEE ( aspects of the Sloan Digital Sky Survey are studying the structure and chemical composition of the halo and disk, as well as nearby dwarf companion galaxies to our Milky Way. We can probe the hot gas in the halo of the Milky Way via the absorption lines it imprints in the spectra of distant hot stars and quasars (Jenkins, Bowen).

There is a major computational effort in the department to model the formation and evolution of galaxies through large-scale simulations (Ostriker, Cen, Bode). Increasingly realistic numerical simulations are now beginning to be possible based on initial conditions taken from the standard cosmology and following galaxy formation with the inclusion of gas dynamics and radiation transfer. Initial successes have been reached in creating massive systems that resemble real elliptical galaxies, but the formation of spirals remains beyond our reach. There is also a strong interest in exploring questions of galaxy evolution and dynamics using analytic or semi-analytic techniques (Ostriker, Spergel, Gunn, Tremaine), with particular interest in the growth of black holes and in the angular momenta and sizes of disk galaxies.

Department Faculty Members With Major Research Interests In Extragalactic Astronomy: