We review the technical aspects of how the 6.5 meter James Webb Space Telescope
(JWST) can measure First Light, Reionization, Galaxy Assembly, building on
lessons learned from the Hubble Space Telescope (HST). We show what combination
of area, depth, and wavelength coverage are needed for JWST to detect a
sufficient number of First Light objects, and to measure their evolving
luminosity function (LF). In detail, JWST will map the epoch of First light
through Pop III star dominated objects at redshifts z=8--20, and its transition
to the first Pop II stars in dwarf galaxies. JWST will measure the evolution of
the steep faint-end of the dwarf galaxy LF at z=6--12, which likely provided
the UV-flux needed to start and finish reionization.
We will discuss: 1) what deep JWST images will look like compared to the Hubble
UltraDeep Field (HUDF), given JWST's expected PSF performance; (2) simulations
of what nearby galaxies observed in their restframe UV--optical light by HST
would look like to JWST at very high redshifts; (3) quantitative methods to
determine structural parameters of faint galaxies in deep JWST images as a
function of cosmic epoch to delineate the progress of galaxy assembly; (4) to
what extent JWST's short-wavelength performance --- which needed to be relaxed
in the 2005 redefinition of the telescope --- will affect JWST's ability to
accurately determine faint galaxy parameters; and (5) if ultradeep JWST images
will run into the instrumental and natural confusion limits. A new generation
of algorithms may be needed to automatically detect, measure and classify
objects in very crowded, ultradeep JWST fields.
We demonstrate an interactive web-tool on a laptop that lets the user pan and
zoom 3-D through the HUDF data-base from redshifts z=0 to z=6, with all galaxy
images sorted versus spectro-photometric redshift, and visualize what JWST
will add from AB=29.5-32 mag and between redshifts z=7-20.
This work was funded by NASA JWST Interdisciplinary Scientist grant NAG5-12460
from GSFC, and grant HST/ED14-975 from STScI, operated by AURA for NASA under
contract NAS 5-26555.