IR Compendium: Background: Comparisons to Spitzer || SPITZER HOME || SPITZER SCIENCE || COMPENDIUM HOME || EXAMPLES INDEX ||

Spitzer is orders of magnitude more capable than any previous infrared observatory, when one considers a combination of its wavelength coverage, sensitivity, angular resolution, detector array sizes, and lifetime.

The useful figures below have been extracted from the SOFIA web site. Note that the photometric sensitivities are for one hour of integration time. In practice, Spitzer will often reach confusion limits in considerably shorter times. For example, in a medium-background environment, the two shortest IRAC channels at 3.6 and 4.5 microns will become (1 sigma) confusion-limited in about 200 seconds and 600 seconds, respectively. For MIPS, the confusion limits are highly uncertain, but are likely to be reached in a matter of minutes when using the photometry mode.

The following three useful plots come from the SOFIA website.

A comparison of several different infrared surveys. Note that the Spitzer numbers are 5-sigma estimates, with a December 2003 understanding of performance, and some rough guessing on confusion, etc.

Influence of resolution on deep far-infrared confusion-limited surveys: 70 microns. These are simulations of a 34 arcminute square sky at 70 microns by H. Dole (U. Arizona). The simulations are at IRAS resolution (~70 arcsec), ISO/PHOT resolution (~40 arcsec), and Spitzer/MIPS resolution (~15 arcsec). The simulation contains ~400,000 extragalactic sources between 1 microJy and 2 Jy, with a foreground of galactic cirrus with a N(H) column density of about 10^20 per square cm.

Influence of resolution on deep far-infrared confusion-limited surveys: 160 microns. These are enlargements of simulations of a 34 arcminute square sky at 160 microns by H. Dole (U. Arizona). These images are a 6.7 arcminute square extracted from these simulations. The simulations are at IRAS resolution (~200 arcsec), ISO/PHOT resolution (~100 arcsec), and Spitzer/MIPS resolution (~50 arcsec). The simulation contains ~600,000 extragalactic sources between 1 microJy and 2 Jy, with a foreground of galactic cirrus with a N(H) column density of about 10^20 per square cm.

Additional views of the 160 micron simulated sky, observed at different resolutions. Left to right, they are DIRBE (45 arcminute pixels), ISO (90 arcsecond pixels), and MIPS (45 arcsecond pixels).

Additional views of the 70 micron simulated sky, 1-hour exposure, observed at different resolutions with different instruments. Note that the simulated SOFIA exposure is dominated by background noise from the (warm) telescope.