Astronomers are piecing together a 12-billion-year fossil record of how galaxies like the Milky Way were built, using three separate lines of observation that span cosmic time. The problem is that no single telescope or technique can tell the whole story of galaxy formation. Observations of nearby stars in the Milky Way and its companion galaxies reveal a detailed fossil record of how galaxies assembled, formed stars, and built up heavy elements. At the other extreme, telescopes looking back more than 12 billion years capture galaxies as they were when the universe was young. And measurements of star formation and gas flows in nearby galaxies provide the crucial middle ground, linking the two. This is fundamental science with no immediate practical application. If successful, it will produce a coherent picture of how galaxies—including our own—came to look the way they do. That deeper understanding of cosmic structure formation has historically fed into unexpected areas, from computational fluid dynamics to the physics of gas accretion that governs how matter organises itself across scales.
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This programmatic five-year rolling grant application addresses one of the most important problems in extragalactic astronomy, the formation and evolution of galaxies, one of the ``big questions'' in the current PPARC Road Map, and is a defining objective of virtually every national decadal survey of astronomy. A full understanding of galaxy formation and evolution requires multiple lines of attack. Observations of the resolved stellar populations in the Milky Way and its Local Group companions provide a detailed fossil record of the dynamical assemblies of the galaxies, the formation of stars, and the buildup of heavy elements over a wide range of mass scales and initial conditions. At the other end of the scale, observations of distant galaxies spanning lookback times of up to 12 Gyr provide direct measurements of the evolution of galaxy populations and the buildup of stars and metals with cosmic time. Finally, measurements of the large-scale star formation and abundance properties of nearby galaxies form a vital astrophysical bridge between the studies of nearby resolved stellar populations and the distant high-redshift investigations, by allowing us to characterise the evolutionary properties of the Hubble sequence and the complex ``gastrophysical'' processes that regulate the accretion of gas and the formation of stars in galaxies. In this rolling grant application we propose a series of investigations that will advance our understanding of galaxy formation and evolution on all three fronts.
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