AAS 195th Meeting, January 2000
Session 86. NGST
Display, Friday, January 14, 2000, 9:20am-6:30pm, Grand Hall

## [86.04] Using a Multi Object Spectrograph (MOS) with a Low-Resolution Prism on NGST to Determine Redshifts

E. M. Malumuth (Raytheon ITSS/GSFC), H. I. Teplitz (NOAO/GSFC), B. E. Woodgate, S. H. Moseley, J. P. Gardner, R. A. Kimble, C. W. Bowers (NASA/GSFC), A. S. Kutyrev, R. K. Fettig (Raytheon ITSS/GSFC), R. P. Wesenberg, J. E. Mentzell (NASA/GSFC)

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 \mu 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.

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