• What are the flows of matter and energy in the circumgalactic medium? This question concerns the understanding of the circumgalactic medium that is needed to understand the mass, energy, and chemical feedback cycle that appears to shape the growth of galaxies and the metal enrichment of the universe. In this report the panel identifies a program of detailed observations of the accretion and outflow processes in nearby galaxies that can inform the understanding of these processes at all epochs and mass scales.

  • What controls the mass-energy-chemical cycles within galaxies? This question explores the rich system of gas and stellar physics that shapes, and is shaped by, the interstellar medium. The panel outlines multiwavelength and theoretical studies of gas, dust, and magnetic fields within galaxies. Such studies can unravel the complexities of the gaseous ecosystem, with a level of detail critical to isolating the relevant physics but that cannot be obtained outside the galactic neighborhood.

  • What is the fossil record of galaxy assembly from first stars to present? This question focuses on probes of the fossil record of star formation, galaxy assembly, and the first stars. The panel identifies the value of surveys for resolved stars at high spatial resolution, with spectroscopic follow-up of stellar populations and metalpoor halo stars providing high-impact science unique to the galactic neighborhood. Furthermore, this fossil record promises to reveal the properties of galaxies at epochs where they cannot be seen directly.

  • What are the connections between dark and luminous matter? This question addresses the use of the galactic neighborhood as a laboratory of fundamental physics. The local universe offers the opportunity to isolate the nearest and smallest dark matter halos and to study astrophysically “dark” systems at high spatial resolution. The panel discusses the many observational and theoretical advances that could be expected as a result of these unique capabilities.

The prospects for advances in the coming decade are especially exciting in these four areas, particularly if supported by a comprehensive program of theory and numerical calculation, together with laboratory astrophysical measurements or calculations. The sections that follow this Summary describe the unresolved scientific issues in more detail, highlighting specific observational and theoretical programs that offer significant opportunities for advancing scientific understanding. Also highlighted is the discovery potential of time-domain astronomy and astrometry for capitalizing on powerful new techniques and facilities that provide precise connections among stars, galaxies, and newly discovered transient events.

Highlights of Top Activities Identified by the Panel

To make significant progress in addressing the four science questions, the panel suggests a broad program of ground-based and space-based science, together with



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