Mathematics – Logic
Scientific paper
Jan 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990ngst.conf...39g&link_type=abstract
The Next Generation Space Telescope, p. 39
Mathematics
Logic
Hubble Space Telescope, Galaxies, Galactic Evolution, Simulation, Astronomical Photography, Galactic Structure, Astronomical Spectroscopy, Apertures, Ccd Cameras, Red Shift, Signal To Noise Ratios
Scientific paper
One of the most-heralded abilities which the Hubble Space Telescope (HST) will bring us is the capability to study the morphologies of quite distant galaxies, distant enough that the look-back time is a substantial fraction of the age of the universe. It appears that with substantial expenditure of observing resources, crude morphological information can be obtained out to redshifts approaching unity, with quite good images at, say, z=0.5. Most theories of galaxy formation, and indeed the growing body of ground-based spectroscopic evidence, put the epoch of galaxy formation earlier, though the weight of modern evidence is that it is not much earlier, and the redshift range 2-3 promises to be of enormous interest. HST, by reason of its small collecting area and, to some extent, limited resolution, cannot address this problem directly. The awesome capability of a fifteen-meter diffraction-limited telescope in high orbit, however, would allow us to see what is going on at these epochs directly and with considerable ease-if still requiring a great deal of observing time. The report presents some simple simulations of observations done with an instrument with the following properties: 16-meter aperture, f/20 modified Ritchey optical system - the scale is 1.45 microns/mas, 5 arcmin diffraction - limited field; this can be easily achieved with a single-element refractive astigmatism corrector, FWHM = 10 mas or about 15 microns at V, Camera with 3 reflections and 1 transmissive element, 8192 x 8l92 CCD with 7.5 micron pixels; the focal plane might be paved with 25 of these devices; each has a field 40" square, Read noise of 2.5 electrons RMS for the CCD, and for the near IR, a 1024 x 1024 HgCdTe device with 40 micron pixels would give a field of 30 arcseconds with 25 mas pixels; it seems likely that a read noise of 10 electrons will be attainable.
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