BOX 7.1

Implementing a Cosmic Dawn Science Plan

  • Carry out simulations and theoretical calculations to motivate and interpret observations aimed at understanding our cosmic dawn.

  • Find and explore the epoch of reionization using hydrogen line observations starting with the HERA telescopes that are already under construction.

  • Use CCAT to identify the best candidate young galaxies for study with submillimeter observations.

  • Study these galaxies in detail using ALMA; in particular, monitor how fast the gas that they contain is being converted into stars.

  • Use JWST to measure the rate at which stars are being formed out of gas, and understand their role in reionizing the universe.

  • Use GSMT to study the early evolution of infant galaxies using optical and infrared spectroscopy.

  • Use GSMT and IXO to monitor the exchange of gas between the galaxies and the surrounding intergalactic medium.

  • Study the rate of formation and growth of black holes in the nuclei of young galaxies using IXO and WFIRST.

  • Employ LISA to measure the rate at which young galaxies merge through observing powerful bursts of gravitational radiation produced during the coalescence of their nuclear black holes.

  • Study the oldest stars in nearby galaxies using GSMT.

NOTE: ALMA, Atacama Large Millimeter/submillimeter Array; CCAT, formerly the Cornell-Caltech Atacama Telescope; GSMT, Giant Segmented Mirror Telescope; HERA, Hydrogen Epoch of Reionization Array; IXO, International X-ray Observatory; JWST, James Webb Space Telescope; LISA, Laser Interferometer Space Antenna; and WFIRST, Wide-Field Infrared Survey Telescope.

Although our own solar system has four such terrestrial bodies, the frequency of formation of terrestrial planets, mass distributions as a function of stellar mass, and orbital arrangements are not understood. Generating a census of Earth-like or terrestrial planets is the essential first step toward determining whether our own home world is a commonplace or rare outcome of planet formation.

We have various complementary means of building up a census of Earth-like planets. The ground-based radial velocity and transit surveys are most sensitive to large planets with small orbits, as is the Kepler satellite, although it should be capable of detecting Earth-size planets out to almost Earth-like orbits. Together these techniques will determine the probability of planets with certain orbital characteristics around different types of stars. To complete the planetary census, it will be necessary to use techniques that are sensitive to Earth-mass planets on large orbits. One such technique is called gravitational microlensing, whereby the pres-

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