AAS 204th Meeting, June 2004
Session 33 Early Science Results from the Spitzer Space Telescope
Topical Session, Tuesday, June 1, 2004, 8:30-10:00am, 10:45am-12:30pm, 2:30-4:00pm, 4:15-6:00pm, 601

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[33.10] IRAC Extragalactic GTO Program: From Nearby Galaxies to the High Redshift Universe

M.A. Pahre, M.L.N. Ashby, P. Barmby, G.G. Fazio, J.-S. Huang, H.A. Smith, Z. Wang, S.P. Willner (CfA), J.L. Pipher, W.J. Forrest (U. Rochester), R.G. Arendt, D.J. Fixsen, S.H. Moseley (NASA/GSFC), P.R.M. Eisenhardt, M. Brodwin, V. Gorjian, D. Stern (JPL), E.V. Tollestrup (NASA/IRTF), E.L. Wright (UCLA)

The IRAC Guaranteed Time Observations program was conceived to study both normal and unusual galaxies from the local universe through their evolution to the early universe.

IRAC imaging of nearby, normal galaxies demonstrates that they can be classified more easily than at visual wavelengths by comparing the stellar light imaged at 3.6 and 4.5 \mum, and the warm dust in the ISM emitting via PAH lines in the 5.8 and 8.0 \mum bands. The PAH luminosity is found to correlate with the star formation rate, which provides a power tool for measuring the cosmological SFR both locally and at higher redshifts. The faint, but detectable, dust emission in early-type galaxies has been resolved in a number of cases to be organized into spiral arms, which is either indicative of ongoing star formation or a relic of their star formation history. Emission from an AGN can be separated from the bulge and disk components both spatially and via easily discernible colors.

At intermediate redshifts, colors in the IRAC bands provide a powerful means of segregating galaxies by redshift and spectral type. Mid-infrared extragalactic source counts show the same flattening of the slope at faint fluxes as has been found in the near-infrared. Due to the redshifted 1.6 \mum SED ``bump'' passing through the IRAC bands, shallow and deep surveys find a large population of z ~1--2 galaxies, sampling well down the luminosity function. At the highest redshifts in deep images, IRAC detects most of the submillimeter and Lyman-break galaxy populations, and provides a direct tracer of the mass of their stellar populations via the rest-frame near-infrared light.

M.A.P. acknowledges NASA/LTSA grant # NAG5-10777, and the IRAC GTO program is supported by JPL Contract # 1256790.

The author(s) of this abstract have provided an email address for comments about the abstract: mpahre@cfa.harvard.edu

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