We discuss the utility of a low resolution prism as a component of a Multi-Object Spectrometer (MOS) for NASA's proposed Next Generation Space Telescope (NGST). Low resolution prism spectroscopy permits simultaneous coverage of the 0.6-5 μ m regime at R<50. Such data can take advantage of the modern techniques in spectral energy distribution (SED) fitting to determine source redshifts, sometimes called ``photometric redshifts''. We compare this approach with other spectroscopic and photometric modes being considered for NGST. Low resolution prism observations of galaxy SED's provide a significant advantage over multi-filter observations for any realistic observing strategy. For an ideal prism in background limited observing, the prism has a signal-to-noise advantage of square root of the resolution over serial observations by filters with similar resolution. This added depth reaches at least a magnitude fainter in recovery of photometric redshifts with the prism over filter observations at similar resolving power. Extensive simulations suggest that in 105 seconds an ideal prism will recover the redshift of 80% of measured objects (subject to MOS selection) down to KAB=32 compared to 40% of the objects with serial filter observations of equal total observing time, while reducing the percent of outright failures from 15% to 1%. The advantage is even greater for the subset of galaxies between KAB=30 and KAB=32.
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1999