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Sara Heap (NASA's GSFC), Don Lindler (Sigma, Inc.), Thierry Lanz (U. MD & NASA's GSFC)
New instrumentation such as DEIMOS on Keck-II now enable deep spectral surveys, and thereby samples of galaxies at younger ages. At a redshift, z=1, all galaxies are less than 6 Gyr old and hence, have not yet formed horizontal-branch stars. Also, at z=1, the restframe-UV comes into view, and with it, a new set of spectral diagnostics. UV spectral features are especially important because most of the UV flux comes from stars at the main-sequence turnoff (MSTO). Hence, UV spectral diagnostics enable the ages of z=1 galaxies to be estimated directly from MSTO stars.
In preparation for these high-redshift spectral surveys, we are developing UV spectral templates for stellar populations younger than 6 Gyr using UV-optical spectra of stars observed by HST/STIS. We are also planning to supplement these observations with theoretical spectral grids of stars of various metallicities. In this paper, we present a progress report on the observation-based spectral templates and spectral diagnostics.
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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.