NASA Scientific and Technical Aerospace Reports

The question "How did we get here and what will the future bring?"captures the human imagination and the
attention of the National Academy of Science’s Astronomy and Astrophysics Survey Committee (AASC). Fulfillment of this
fundamental goal requires astronomers to have sensitive, high angular and spectral resolution observations in the
far-infrared/submillimeter (far- IR/sub-mm) spectral region. With half the luminosity of the universe and vital information
about galaxy, star and planet formation, observations in this spectral region require capabilities similar to those currently
available or planned at shorter wavelengths. In this paper we summarize the scientific motivation, some mission concepts and
technology requirements for far-IR/sub-mm space interferometers that can be developed in the 2010-2020 timeframe.
Author
Infrared Interferometers; Cosmic Dust; Astronomical Observatories
20040074289 Jet Propulsion Lab., California Inst. of Tech., Pasadena, CA, USA
The Case for Space-Borne Far-Infrared Line Surveys
Bock, J. J.; Bradford, C. M.; Dragovan, M.; Earle, L.; Glenn, J.; Naylor, B.; Nguyen, H. T.; Zmuidzinas, J.; New Concepts
for Far-Infrared and Submillimeter Space Astronomy; April 2004, pp. 205-213; In English; See also 20040074260; No
Copyright; Avail: CASI; A02, Hardcopy
The combination of sensitive direct detectors and a cooled aperture promises orders of magnitude improvement in the
sensitivity and survey time for far-infrared and submillimeter spectroscopy compared to existing or planned capabilities.
Continuing advances in direct detector technology enable spectroscopy that approaches the background limit available only
from space at these wavelengths. Because the spectral confusion limit is significantly lower than the more familiar spatial
confusion limit encountered in imaging applications, spectroscopy can be carried out to comparable depth with a significantly
smaller aperture. We are developing a novel waveguide-coupled grating spectrometer that disperses radiation into a wide
instantaneous bandwidth with moderate resolution (R ~ 1000) in a compact 2-dimensional format. A line survey instrument
coupled to a modest cooled single aperture provides an attractive scientific application for spectroscopy with direct detectors.
Using a suite of waveguide spectrometers, we can obtain complete coverage over the entire far-infrared and sub-millimeter.
This concept requires no moving parts to modulate the optical signal. Such an instrument would be able to conduct a
far-infrared line survey 10 6 times faster than planned capabilities, assuming existing detector technology. However, if
historical improvements in bolometer sensitivity continue, so that photon-limited sensitivity is obtained, the integration time
can be further reduced by 2 to 4 orders of magnitude, depending on wavelength. The line flux sensitivity would be comparable
to ALMA, but at shorter wavelengths and with the continuous coverage needed to extract line fluxes for sources at unknown
redshifts. For example, this capability would break the current spectroscopic bottleneck in the study of far-infrared galaxies,
the recently discovered, rapidly evolving objects abundant at cosmological distances.
Author
Infrared Telescopes; Sensitivity; Infrared Spectrometers
20040074292 Naval Research Lab., Washington, DC, USA
IR Fine-Structure Line Signatures of Central Dust-Bounded Nebulae in Luminous Infrared Galaxies
Fischer, J.; Allen, R.; Dudley, C. C.; Satyapal, S.; Luhman, M.; Wolfire, M.; Smith, H. A.; New Concepts for Far-Infrared and
Submillimeter Space Astronomy; April 2004, pp. 109-116; In English; See also 20040074260; No Copyright; Avail: CASI;
A02, Hardcopy
To date, the only far-infrared spectroscopic observations of ultraluminous infrared galaxies have been obtained with the
European Space Agency s Infrared Space Observatory Long Wavelength Spectrometer. The spectra of these galaxies are
characterized by molecular absorption lines and weak emission lines from photodissociation regions (PDRs), but no
far-infrared (greater than 40 microns) lines from ionized regions have been detected. ESA s Herschel Space Observatory,
slated for launch in 2007, will likely be able to detect these lines in samples of local and moderate redshift ultra luminous
galaxies and to enable measurement of the ionization parameters, the slope of the ionizing continuum, and densities present
in the ionized regions of these galaxies. The higher spatial resolution of proposed observatories discussed in this workshop
will enable isolation of the central regions of local galaxies and detection of these lines in high-redshift galaxies for study of
the evolution of galaxies. Here we discuss evidence for the e.ects of absorption by dust within ionized regions and present the
spectroscopic signatures predicted by photoionization modeling of dust-bounded regions.
Author
Cosmic Dust; Fine Structure; Galactic Evolution; Infrared Radiation; Luminosity; Nebulae
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