• How do cosmic structures form and evolve?

  • How do baryons cycle in and out of galaxies, and what do they do while they are there?

  • How do black holes grow, radiate, and influence their surroundings?

  • What were the first objects to light up the universe and when did they do it?

  • Unusual discovery potential: the epoch of reionization.

To maximize progress in addressing these issues, the panel considered the wide array of observational and theoretical programs made possible by current or future facilities. Observational programs were discussed in sufficient detail to allow an understanding of the requirements (numbers of objects, sensitivity, area, spatial resolution, energy resolution, etc.) so that this panel could provide the most useful input to the study’s Program Prioritization Panels (PPPs; see the Preface for further information on this process); however, any assessment of the suitability of existing or proposed facilities to the key science issues outlined here is left to the PPPs and the survey committee.

This report describes the scientific context for the area “galaxies across cosmic time,” and identifies the key science questions in this area for the next decade and a set of science programs—observational and theoretical—that will answer the most important questions in the field. Some of these programs would require new observational facilities, whereas others could be done with existing facilities, possibly with a reprogramming of resources. In order to provide more useful input to the Astronomy and Astrophysics 2010 (Astro2010) Survey, the top science programs selected by the panel for purposes of this report are identified in three categories: most important, very important, and important. The panel considered many other programs that were eventually excluded from its list but that remain valuable ways to make progress, and it anticipates that significant progress will also come from unexpected directions.

This Summary addresses each of the four key questions in turn, listing only the programs ranked “most important,” plus those “very important” activities that represent unique capabilities. The full set of the panel’s top-ranked science programs is summarized in Table 3.1 at the end of this “Summary” section and is presented with rankings and further details in the body of the report.

How Do Cosmic Structures Form and Evolve?

The answer to this question starts with an understanding of the structure of dark matter halos on all scales. The now-standard lambda cold dark matter—ΛCDM—cosmology provides a detailed foundation on which a theory of galaxy formation and evolution can be built and which in turn can be tested by data.

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