TPF-I SWG Report - Exoplanet Exploration Program - NASA

C HAPTER 3
Continuum interferometry will map the circum-nuclear distributions of stars. Synchrotron emission
produced by relativistic particles gyrating in nuclear magnetic fields will trace non-thermal continua. The
distributions of silicate dust, ices, and PAHs can be used to trace the warm-gas and dust distributions in
the circum-nuclear environments of AGN with unprecedented resolution.
Interferometric measurements of the lensed objects may provide the highest resolution studies of stars and
interstellar media in the distant Universe. By combining the milli-arcsecond resolution of Darwin/TPF-I
with the natural magnification of a gravitational lens, linear resolutions of less than 1 pc can be achieved
in the high-redshift Universe.
3.2.4 Galaxy Formation and Evolution
Current galaxy-formation models assume that the large-scale mass distribution in the early Universe is
driven by the gravity exerted by dark matter. The evolution of the dark-matter distribution follows from
conditions in the early Universe. Gas dynamics, shocks, and radiative heating and cooling all play
fundamental roles in the emergence of the first stars and proto-galaxies. The first stars are thought to be
massive (10 to 100 Solar masses), and hotter than their modern counterparts. Thus, the first stars are
though to create giant HII regions whose red-shifted hydrogen and helium emission lines should be
readily observable by Darwin/TPF-I.
While NASA’s JWST is expected to make the first detections of these objects, its angular resolution will
be limited to the diffraction spot size of its 6.5-m primary mirror, about 0.2”. Darwin/TPF-I will resolve
scales of order 10 to 100 pc at all redshifts. The IR response will enable the detection of rest-frame near-
IR to visual wavelength emission at very high redshifts (z > 5). Thus, Darwin/TPF-I will provide the
hundred-fold gain in resolution needed to resolve these primordial HII regions. Models suggest that the
birth of the very first stars may inhibit further star formation until these primordial stars die, a few million
years after their birth. High angular resolution follow-up of JWST-detected “First Light” objects by
Darwin/TPF-I will test the current paradigm for the formation of the first stars. Are they truly isolated,
single objects, or are they surrounded by young clusters of stars
Soon after the formation of the very first stars, their supernovae will pollute the surrounding medium,
causing the condensation of dust. Dust heated by starlight, and the HII regions surrounding the very first
stars will be visible and resolvable by Darwin/TPF-I. Subsequent growth of primordial galaxies occurs
by a combination of merging and in-fall of primordial gas.
The baryonic matter in young galaxies is expected to be dominated by gas. As the first generations of
stars explode in supernova explosions, they will pollute their environments with metals. Dust and
molecule formation will drive star formation to increasingly resemble star formation in the current epoch.
Hot dust, giant HII regions, and warm molecular clouds are expected to emerge. Darwin/TPF-I will play
a crucial role in mapping the distributions of stars, clusters, super-giants, post-main sequence stars,
supernovae, and emerging black holes in the highest redshift galaxies being detected at sub-mm
wavelengths with today’s instruments (Smail et al. 1997, Hughes et al. 1998, Barger et al. 1998) or in the
future by the Atacama Large Millimeter Array (ALMA) and in the thermal IR by JWST.
Darwin/TPF-I will be especially sensitive to forming super-star clusters, the suspected progenitors of
today’s globular cluster systems. While JWST may detect galaxies containing such clusters at high red-
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