|Hubble Deep Field - North
The unprecedented sensitivity and efficiency of Spitzer makes the observatory an ideal tool for conducting surveys of the extragalactic (external to our Milky Way) infrared sky. Early in its mission, Spitzer will conduct a variety of mid- and far-infrared imaging surveys. Deep and small-area surveys, including one centered on the northern Hubble Deep
Field, will probe the early and distant Universe at redshifts approaching 5, corresponding to a distance of about 12 billion light years. Shallower surveys will also be conducted over larger areas, vastly increasing the number of cataloged infrared galaxies. One survey will cover about 70 square degrees, or 350 times the area of the full Moon, out to redshifts of 2.5 (about 10 billion light years). This survey will reveal more than two million galaxies, or nearly 30,000 galaxies per square degree. As with any extragalactic survey, the utility of the Spitzer data will be greatly enhanced by companion observing programs at other wavelengths and with other space-borne and ground-based telescopes.
|Evolution of Galaxies
Montage Courtesy of NASA/IPAC/C. Lonsdale
Origin and Evolution of Galaxies
At a cosmological redshift of 5, the visible light emitted by young galaxies
is redshifted to near-infrared wavelengths, placing them within Spitzer's
observational regime. Astronomers will exploit this capability to observe dusty protogalaxies being born in the young and distant Universe. By examining galaxy properties at different redshifts, or cosmological ages, scientists will trace the history of star formation as a function of environment, and try to explain why the global star formation rate was much higher seven billion years ago. These data will also enable studies of the spatial distribution and clustering of galaxies. Moreover, Spitzer data (when combined with x-ray data) will permit
astronomers to ascertain the extent to which starburst galaxies and dusty
active galactic nuclei contribute to the global infrared luminosity.
|All-Sky Maps of the Infrared Background
Cosmic Infrared Background
The cosmic infrared background (CIRB) is a very faint infrared glow in
the distant Universe, presumably produced by the juxtaposition of countless
unseen galaxies that are too faint to be detected individually. By studying
the intensity of the CIRB at different wavelengths, astronomers can
interpret the history of star formation, the history of galaxy formation, and
the presence or absence of dust in the earliest primeval galaxies. Spitzer
should not only confirm the recent detections of this background light, but
will characterize the sources(s) of this radiation.
|Submillimeter Image of Hubble Deep Field - North
Optically Unidentified IR Sources
It is a well-known observation that some celestial sources emit more (if not
most) of their radiation at particular wavelengths. It is certain that Spitzer
will discover unusual infrared sources with no known optical counterpart.
Spectroscopic measurements with Spitzer will allow astronomers to obtain
the redshift, and hence the inferred distance, of these mysterious objects.
The Spitzer data will be combined with observations at other wavelengths,
such as x-ray and radio, to aid in the interpretation of the unidentified
Spitzer's powerful combination of great sensitivity, high observing
efficiency, large-format detector arrays, and a long cryogenic lifetime
represents a giant leap beyond current capabilities. This potent
combination will produce a rich legacy of scientific results that will be
studied for decades. As history has repeatedly shown, astronomers can
also expect the unexpected: serendipitous discoveries of unanticipated