The Spitzer Legacy Program:

Mark Dickinson, PI
NOAO
950 N. Cherry Ave.
Tucson AZ 85719

The Great Observatories Origins Deep Survey (GOODS) incorporates a Spitzer Legacy project designed to study galaxy formation and evolution over a wide range of redshift and cosmic lookback time. The project will trace the mass assembly history of galaxies, the evolution of their stellar populations, and the energetic output from star formation and active nuclei. GOODS builds on the deepest observations from NASA's other Great Observatories, Hubble and Chandra, and will be done in partnership with astronomers at Gemini and ESO, with a commitment of extensive ESO and NOAO observing time. By observing at lambda > 3 um, Spitzer will measure the rest-frame near- and mid-infrared light from objects at 1 < z < 6, but very deep observations are needed to detect "ordinary" galaxies at these high redshifts.

GOODS will survey approximately 300 square arcmin divided into two fields: the Hubble Deep Field North and the Chandra Deep Field South. These are among the most data-rich portions of the sky, and are the sites of the deepest observations from Hubble, Chandra, ESA's XMM-Newton, and from many ground-based facilities. Dividing our survey area provides insurance against cosmic variance due to galaxy clustering, and guarantees that astronomers in both hemispheres can carry out related observations. GOODS will image these fields at 3.6-8 um with IRAC, with a mean exposure time per position of approximately 25 hours per band, reaching far deeper flux limits than observations planned for the Guaranteed Time programs. 10 hour exposures with MIPS at 24 um are also planned, pending on-orbit tests to establish that the data will achieve a significant gain in sensitivity relative to planned 20 minute GTO exposures. Finally, a pair of ultradeep IRAC fields are planned for the HDF-N, with total exposure times up to 100 hours, again pending on-orbit demonstration of instrument performance and source confusion.

The GOODS IRAC observations are designed to detect rest-frame near-infrared light from the progenitors of galaxies like the Milky Way out to z=4, and will enable us to measure the stellar mass distribution of galaxies through most of cosmic history. The smaller, ultradeep IRAC field will probe the faintest sources and highest redshifts. The MIPS observations will offer the best opportunity to detect emission from dust-obscured star formation in ordinary galaxies out to z=2.5, and, in concert with the Chandra data, will enable a census of supermassive central black holes in obscured and unobscured AGN. Overall, the data will provide the best lower limits to the extragalactic background light at 3.6-24 um. By combining space- and ground-based observations, we will create a public data archive extending from X-ray through radio wavelengths, with a large sample of objects out to the highest known redshifts. This survey will give a uniquely comprehensive history of galaxies, from early epochs to the relatively recent past, and will serve as a bridge to future exploration in these wavelength and redshift regimes with the Next Generation Space Telescope.

The HST Treasury Program:

Mauro Giavalisco, PI
STScI
3700 San Martin Dr.
Baltimore, Maryland, 21218

The GOODS HST Treasury Program will use the new Advanced Camera for Surveys (ACS) to image the two GOODS fields through four broad, non-overlapping filters: F435W (B), F606W (V), F775W (i), and F850LP (z). The exposure times will be 3, 2.5, 2.5 and 5 orbits per filter, respectively, reaching extended-source sensitivities within 0.5-0.8 mags of the WFPC2 HDF observations. GOODS is a deep survey, not a wide one, but it is much larger than most previous, deep HST/WFPC2 surveys, covering 320 square arcmin, 32x the combined solid angles of the HDF-N and S, and 4x larger than their combined flanking fields. The Viz imaging will be taken in five repeat visits separated by approximately 45 days, enabling a search for SNe Ia at 1.2 < z < 1.8 to test the transition from cosmic deceleration to acceleration predicted in world models dominated by dark energy. The z-band observations will image the optical rest-frame light from galaxies out to z = 1.2, with angular resolution superior to that from WFPC2. Combined GOODS data from HST, Spitzer, Chandra, and ground-based observatories will make it possible to map the evolution of the Hubble sequence with redshift, reconstructing the history of galaxy mass assembly, star formation and nuclear activity. The ACS BViz imaging will enable a systematic survey of Lyman break galaxies at 4 < z < 6.5, reaching back to the suggested epoch of reionization. The HST data will also provide a powerful tool to study the dark matter mass around galaxies using gravitational lensing, to search for low-mass stars in our own galaxy, and perhaps to detect moving objects in the outer solar system.

Layout of the GOODS fields	Schematic illustration of the fields covered by Spitzer
Legacy project description:	A five page summary (PDF format) of the GOODS/Spitzer project included in the booklet of "extended abstracts" for the Legacy programs, distributed by the SSC at the June 2001 AAS meeting in Pasadena.
GOODS in Venice:	Contributions to proceedings for the October 2001 conference on "The Mass of Galaxies at Low and High Redshift": Dickinson & Giavalisco "The Great Observatories Origins Deep Survey" Renzini et al. "ESO for GOODS' Sake"
STScI Newsletter:	Spring 2002 issue of the STScI Newsletter, featuring stories on the HST Treasury programs, including GOODS (see page 1). Whole newsletter, or GOODS article only.
ESO Messenger:	A short article from The ESO Messenger, issue no. 105, pp. 40-41, describing GOODS and ESO involvement in the project.
GOODS at ESO	The ESO/ST-ECF GOODS web pages
Simulations:	Simulation of a 100 hour Spitzer IRAC observation of the HDF-N at 3.6 to 8 microns, and comparison to a real, in-flight image.
Co-investigators	The culprits.