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GALEX Science
Goals
The primary goals of GALEX are to address these questions:
1. What are the UV properties of local galaxies, and how do rest UV properties, measured at high redshift by HST and NGST in their search for galaxy origins relate to star formation rate (SFR), extinction, metallicity, and burst history?
2. What is the star formation and metal production history of galaxies over the redshift range 0<z<2? When and where did stars and elements we see today have their origins? And does this history explain the dramatic evolution suggested in previous surveys?
3. What global (galaxy-wide) factors drive star formation and its evolution in galaxies?
Method
GALEX addresses these goals with a set of focussed objectives:
Imaging: Two imaging surveys in a Far UV band (1350—1800 Angstroms) and Near UV band (1800—3000 Angstroms) with 3-5 arcsecond resolution (FWHM) and better than 1 arcsecond astrometry, and a cosmic UV background map.
[AIS:] An All-sky Survey to 20-21m (AB), netting ~10,000 galaxies within 70 Mpc and an unbiased local calibration of UV galaxy morphology, SFR, and extinction.
[DIS:] A Deep Imaging Survey over 100 square degrees to 25.5m (AB) to provide photometric redshifts, extinction and SFR for the faintest and most distant galaxies.
[UIS:] An Ultra-deep Imaging Survey over 10 square degrees to 26.5m (AB)
Spectroscopy: Three overlapping slitless-grism Spectroscopic Surveys over the 1350—3000 Angstrom band with l/Dl~100, resulting in greater than 100,000 galaxies with redshifts (0<z<2), extinction, and SFR, with no follow-up required.
[WSS:] A Wide-field Spectroscopic Survey to 20m (AB) over 100 square degrees to calibrate the global UV/SFR/Extinction relations and find the rarest and most luminous star-forming galaxies.
[MSS:] A Medium-deep Spectroscopic Survey to 21.5—23m (AB) over 10 square degrees to find star forming galaxies of intermediate SFR and redshift.
[DSS:] A Deep Spectroscopic Survey to 22.5—24.3m (AB) over 2 square degrees to find thegalaxies with the lowest SFR and highest z, overlapping the deepest ground-based surveys.
GALEX will produce an unprecedented statistically powerful database of UV images and spectra of nearby and distant galaxies. Using UV properties, supplemented by other wavelengths, GALEX will derive global parameters for each galaxy (star formation rate, extinction, initial mass function (IMF), starburst parameters) vs. redshift, characterize their relationship to galaxy properties (luminosity, type, metallicity, neighborhood, gas supply) and their evolution by comparing statistical distributions of these parameters to cosmological models of the history of galaxies and QSOs. GALEX is a high-priority Origins and SEU mission, tracing the origins of the majority of stars, metals, and many galaxies and galaxy disks, providing a framework for understanding HST and NGST rest UV from high z galaxies, and understanding the drivers of galaxy and QSO evolution. Many UV objects HST must study in preparation for NGST will be discovered by GALEX.
