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James Webb Space Telescope
Assembly Of Galaxies

Assembly of Galaxies
The two images at the top show the Hubble Ultra Deep Field obtained with WFC3/IR in three filters.
The two images at the bottom are simulations of what the deep field may look like with JWST/NIRCam.
JWST images will be both sharper and extend to fainter limits compared to Hubble.

Galaxies are the visible building blocks of the universe. Theory and observation also give us a preferred picture of the assembly of galaxies. It seems that small objects formed first, and then were drawn together to form larger ones. This process is still occurring today, as the Milky Way merges with some of its dwarf companions, and as the Andromeda Nebula heads toward the Milky Way for a future collision. Galaxies have been observed back to times about one billion years after the Big Bang. While most of these early galaxies are smaller and more irregular than present-day galaxies, some early galaxies are very similar to those seen nearby today. This is a surprise.

Despite all the work done to date, many questions are still open. We do not really know how galaxies are formed, what controls their shapes, what makes them form stars, how the chemical elements are generated and redistributed through the galaxies, whether the central black holes exert great influence over the galaxies, or what are the global effects of violent events as small and large parts join together in collisions. The JWST Assembly of Galaxies theme goal is to observe galaxies back to their earliest precursors (z > 10) so that we can understand their growth and their morphological and metallicity evolution. The JWST must provide imaging and spectroscopy over the 0.6 to 27 µm band to meet this objective.