Imaging of High-Redshift Submillimeter Galaxies at 16 and 22 microns with the Spitzer Infrared Spectrograph (IRS) Peak-up Cameras: Revealing a population at z > 2.5

We present broadband imaging observations obtained with the ``peak-up'' imagers of the Spitzer Space Telescope Infrared Spectrograph at wavelengths of 16 and 22 μm for a number of sources detected primarily at submillimeter wavelengths, which are believed to be at high, albeit undetermined, redshift. We targeted 11 sources originally detected by SCUBA and five submillimeter sources detected at 1.2 mm by MAMBO. Two optically discovered quasars with z>6 were also observed to determine whether there is detectable dust emission at such high redshifts. Seven of the submillimeter sources and both high-redshift quasars were detected, and upper limits of about ~50 μJy apply to the remainder. Using their mid-/far-IR colors, we demonstrate that all of the submillimeter sources are at z>1.4. The mid-IR colors for two of our detections and three of our strong upper limits suggest that these galaxies must be at z>2.5. We also introduce a technique for estimating redshifts and source characteristics based only on the ratio of fluxes in the 16 and 22 μm images.

The IRS was a collaborative venture between Cornell University and Ball Aerospace Corporation, funded by NASA through the Jet Propulsion Laboratory and the Ames Research Center.