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WFC3
Science White Paper
Panchromatic
Galaxy Evolution
In order to
study the controlling mechanisms of star formation in galaxies
and to learn how to interpret the flood of tantalizing data
on very distant galaxies, often observed in the restframe
UV, we require high quality UV-optical-IR imaging of nearby
objects for which good correlative radio, infrared, and
X-ray data are available. WFC3 is uniquely capable of providing
such imaging. The UV conveys the most information about
the history of star formation over the past 500 Myr and
allows direct detection of the massive stars responsible
for most ionization, photodissociation, kinetic energy input,
and element synthesis in galaxies. The IR traces the mature
stellar population and most of the stellar mass and probes
dusty star forming regions. The panchromatic coverage of
WFC3 from the mid-UV at 2000 A to the near-IR at 18000 A,
with high resolution over a wide field, therefore offers
powerful insights into galaxy evolution.
Detection
of High Redshift Galaxies
WFC3 is particularly
well suited to the detection and study of several important
classes of high redshift galaxies. HST IR imaging is essential
for studying massive elliptical galaxies and the formation
of spiral disks at z > 1. Deep, wide-field, WFC3 IR imaging
can also be used to search for galaxies beyond z = 6, where
the Lyman-alpha forest and Lyman limit completely suppress
the observed optical light. WFC3 has a critical advantage
over ground-based IR telescopes thanks to the dark sky background
in space. Its gain in detection efficiency over WFPC2+NICMOS
will be a factor of ~7x. IR imaging is especially important
for high z galaxies since optical imaging (in the rest frame
far-UV) is biased toward regions of recent star formation,
often containing only a small fraction of the stellar mass.
WFC3's good
UV response also permits exploration of the epoch z ~ 1-3,
during which the final assembly of galaxies and much of
the global astration of primeval gas occurred. This critical
epoch is now badly sampled because of the absence of strong
spectral features in the optical bands. However, both Lyman-alpha
(rest 1216 A) and the Lyman discontinuity (rest 912 A) are
present in the high throughput WFC3 2000-4000 A band at
these redshifts. The improved sampling, together with HST's
excellent resolution, permits study of the merger of sub-galactic
clumps into luminous galaxies and tests theories of galaxy
formation.
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Anatomy
of galaxy NGC2442, from B-band through K-band
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Astrophysics
of the Interstellar Medium
Stellar birth
and death have been major themes of HST observations to
date. WFC3 will carry a large set of narrow-band UV, optical,
and IR filters optimized for study of key diagnostic emission
lines in star forming regions, stellar winds, supernovae
remnants, planetary nebulae, and other interstellar material.
It will extend the spectral range, sensitivity, and field
of view of other HST cameras, opening up the near UV to
deep, wide-field nebular studies for the first time, notably
including the crucial diagnostic feature [O II] 3727. Given
CCD's with lower noise and improved charge-transfer efficiency,
WFC3's gain over WFPC2 may be a factor of 4-12x in limiting
surface brightnesses in narrow bands and yet better in the
UV. HST resolution is essential for the study of the physical
structure of photoionized regions, shock waves, and collimated
flows. WFC3's IR capabilities are critical for evaluating
and construing MHD models of stellar and planetary origins
through the high resolution study of protostellar and protoplanetary
regions.
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